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Morphology of Anomalocaris canadensis from the Burgess Shale
Abstract
Recent description of the oral cone of Anomalocaris canadensis from the Burgess Shale (Cambrian Series 3, Stage 5) highlighted significant differences from published accounts of this iconic species, and prompts a new evaluation of its morphology as a whole. All known specimens of A. canadensis, including previously unpublished material, were examined with the aim of providing a cohesive morphological description of this stem lineage arthropod. In contrast to previous descriptions, the dorsal surface of the head is shown to be covered by a small, oval carapace in close association with paired stalked eyes, and the ventral surface bears only the triradial oral cone, with no evidence of a hypostome or an anterior sclerite. The frontal appendages reveal new details of the arthrodial membranes and a narrower cross-section in dorsal view than previously reconstructed. The posterior body region reveals a complex suite of digestive, respiratory, and locomotory characters that include a differentiated foregut and hindgut, a midgut with paired glands, gill-like setal blades, and evidence of muscle bundles and struts that presumably supported the swimming movement of the body flaps. The tail fan includes a central blade in addition to the previously described three pairs of lateral blades. Some of these structures have not been identified in other anomalocaridids, making Anomalocaris critical for understanding the functional morphology of the group as a whole and corroborating its arthropod affinities.
... Radiodonts have been presumed to have undergone ecdysis during growth, as has been demonstrated for other Cambrian ecdysozoans (Daley and Drage 2016). Several authors have suggested that certain radiodont specimens may represent molts (Briggs 1979;Daley et al. 2013;Daley and Edgecombe 2014;Zeng et al. 2018;Caron 2019b, 2021; Caron and Moysiuk 2021) on the basis of meeting some of the criteria outlined by Daley and Drage (2016) for distinguishing between carcasses and exuviae in the fossil record. However, distinguishing between fossil carcasses and molt remains in animals without close modern analogues is not straightforward. ...
... This differs from the case in Stanleycaris, in which the preocular sclerite is typically missing while the appendages and oral cone may remain associated with the trunk. Some specimens of Anomalocaris ("preservational mode showing setal blades" in Daley and Edgecombe [2014]; Fig. 6A) show shriveled flaps and loss of part of the head region similar to Stanleycaris molts; however, in this case, the head carapace elements typically remain associated with the trunk remains (Moysiuk and Caron 2019b). If these specimens indeed represent exuviae, they are suggestive of subtle interspecific differences in the position of sutures or behavior of the exiting animal, although in all cases sutures must be positioned near the neck-trunk junction. ...
... If these specimens indeed represent exuviae, they are suggestive of subtle interspecific differences in the position of sutures or behavior of the exiting animal, although in all cases sutures must be positioned near the neck-trunk junction. Another peculiarity is that gill lamellae, preserved in carbonaceous mode, are only rarely visible in Stanleycaris exuviae, while they are frequently seen in putative equivalents in Anomalocaris (Daley and Edgecombe 2014). Traces of dorsal cuticular segmentation may also be effaced in exuviae of both species. ...
Radiodonta is a clade of stem euarthropods of central importance to our understanding of the evolution of this phylum. Radiodonts include some of the largest early Paleozoic animals; however, little is known about their ontogeny. We present an analysis of molting patterns and ontogeny in the radiodont Stanleycaris based on 265 exceptionally preserved specimens from the mid-Cambrian (Wuliuan) Burgess Shale. Ranging in size from 10 to 83 mm, they constitute the most extensive radiodont ontogenetic series known. Using a novel morphospace approach, we show that putative carcasses and exuviae can be quantitatively distinguished by the particular suites of structures preserved and their modes of preservation. We propose that Stanleycaris , and probably other radiodonts, molted via a suture near the anterior of the trunk. Similar anterior molting strategies, with a suture located at the head–trunk boundary, are shared with some Cambrian euarthropods and are potentially ancestral. Allometric analyses suggest that as Stanleycaris body size increased, the head sclerite and neck became relatively broader, while the trunk and flaps became slightly longer. The eyes developed precociously, indicating an important role of visual processing in juveniles. Finally, we find evidence for an initial anamorphic developmental phase, where segment number increased at least from 11 or 12 up to 17, followed by an epimorphic phase, in which growth continued without segment addition. This is consistent with the hypothesis that finite postembryonic segment addition (hemianamorphosis) is ancestral for arthropods and refines the timing of the origin of this important developmental mode.
... figure 1a-c,f,g,i; electronic supplementary material, figures S1-S3, S6, S12, S15). Similar mottled textures occur in other animals preserved from the same locality, such as Anomalocaris [30], suggesting a similar taphonomic cause. The mottled textures tend to be expressed only on large specimens, and above internal organs, including the gut and body cavity in Anomalocaris, and the gonads or stomach area in Burgessomedusa. ...
... One specimen is also preserved with both Leanchoilia and Olenoides within its umbrella space (electronic supplementary material, figure S17g,h). If not coincidental, this positioning would suggest that Burgessomedusa was a nektobenthic predator capable of capturing large, motile prey, thus sharing ecospace in the Burgess Shale palaeocommunity with giant arthropod predators such as Anomalocaris [30] and chaetognaths [44]. Burgessomedusa adds to the complexity and diversity of Cambrian marine ecosystems and demonstrates that large ...
... The prolate, box-like shape of the bell provides indirect evidence of rowing propulsion and predatory habit based on cubozoan analogues. Burgessomedusa shows that pelagic Cambrian ecosystems were not uniquely dominated by large arthropod predators such as Anomalocaris [30] and Titanokorys [50], but that they also harboured a diversity of other predators including chaetognaths [44,51], ctenophores [47] and jellyfish. ...
Cnidarians are regarded as one of the earliest-diverging animal phyla. One of the hallmarks of the cnidarian body plan is the evolution of a free-swimming medusa in some medusozoan classes, but the origin of this innovation remains poorly constrained by the fossil record and molecular data. Previously described macrofossils, putatively representing medusa stages of crown-group medusozoans from the Cambrian of Utah and South China, are here reinterpreted as ctenophore-grade organisms. Other putative Ediacaran to Cambrian medusozoan fossils consist mainly of microfossils and tubular forms. Here we describe Burgessomedusa phasmiformis gen. et sp. nov., the oldest unequivocal macroscopic free-swimming medusa in the fossil record. Our study is based on 182 exceptionally preserved body fossils from the middle Cambrian Burgess Shale (Raymond Quarry, British Columbia, Canada). Burgessomedusa possesses a cuboidal umbrella up to 20 cm high and over 90 short, finger-like tentacles. Phylogenetic analysis supports a medusozoan affinity, most likely as a stem group to Cubozoa or Acraspeda (a group including Staurozoa, Cubozoa and Scyphozoa). Burgessomedusa demonstrates an ancient origin for the free-swimming medusa life stage and supports a growing number of studies showing an early evolutionary diversification of Medusozoa, including of the crown group, during the late Precambrian–Cambrian transition.
... The most emblematic fossil group from the Cambrian Explosion is Radiodonta, best represented by Anomalocaris canadensis ( Figure 1C), a giant apex predator of the famous Burgess Shale (Daley and Edgecombe, 2014). Radiodonts, informally called anomalocaridids, are an extinct order of nektonic predators that lived from Cambrian Series 2 Stage 3 to the Early Ordovician, and possibly into the Lower Devonian with the enigmatic Schinderhannes (Kühl et al., 2009;Daley and Legg, 2015;Van Roy et al., 2015;Edgecombe, 2020). ...
... Radiodonts, informally called anomalocaridids, are an extinct order of nektonic predators that lived from Cambrian Series 2 Stage 3 to the Early Ordovician, and possibly into the Lower Devonian with the enigmatic Schinderhannes (Kühl et al., 2009;Daley and Legg, 2015;Van Roy et al., 2015;Edgecombe, 2020). A total of 37 species have been placed in or associated with Radiodonta, and all are predators, even though the predation strategy differs between taxa (Daley and Budd, 2010;Daley et al., 2013a;Daley and Edgecombe, 2014;Van Roy et al., 2015;Moysiuk and Caron, 2021). Radiodonts all have a segmented body with laterally-oriented flaps and setal blades, and a head characterised by a pair of large compound eyes on stalks, a pair of large, segmented frontal appendages, cephalic carapaces, and radially arranged plates surrounding the mouth (Figure 2). ...
... The identification of large cephalic carapaces in the Burgess Shale radiodont taxa Hurdia (Daley et al., 2009;Daley et al., 2013a) and Cambroraster (Moysiuk and Caron, 2019), consisting of a central element and two lateral elements (Figures 6A-E) (Supplementary Table S1A), meant that similar isolated carapaces in numerous Cambrian lagerstätten have found a home within Radiodonta (e.g., Sun et al., 2020a;Pates et al., 2021b) New discoveries of frontal appendages and oral cones have shown that these two anatomical features are highly variable in morphology within the clade, giving opportunities for reconstructions of their feeding paleoecology (Daley and Peel, 2010;Daley et al., 2013b;Vinther et al., 2014;Cong et al., 2016;Cong et al., 2017;Cong et al., 2018;Lerosey-Aubril and Pates, 2018;Pates et al., 2018;Guo et al., 2019;Wu et al., 2021a;Wu et al., 2021b;Wu et al., 2022 and references therein). Whole body specimens of radiodonts remain relatively rare but have been instrumental in describing previously unknown features of their flaps, setal blades and tail fan (Van Roy and Briggs, 2011;Van Roy et al., 2015;Zeng et al., 2022), and internal organs such as the nervous system (Cong et al., 2014;Moysiuk and Caron, 2022) and digestive tract (Daley and Edgecombe, 2014;Vannier et al., 2014). Radiodonts are now know from 34 different lagerstätten from the paleocontinents of Gondwana, Laurentia, South China, North China, Baltica, and Avalonia (Figure 7), with their total diversity of species standing at 37 named species and several more taxonomically uncertain specimens (Supplementary Datasheet S1 and Supplementary Table S2). ...
One of the most widespread and diverse animal groups of the Cambrian Explosion is a clade of stem lineage arthropods known as Radiodonta, which lived exclusively in the early Paleozoic. First reported in 1892 with Anomalocaris canadensis, radiodonts are now one of the best known early animal groups with excellent representation in the fossil record, and are ubiquitous components of Konservat-Lagerstätten from the Cambrian and the Early Ordovician. These large swimmers were characterised by a segmented body bearing laterally-oriented flaps, and a head with a distinct radial oral cone, a pair of large frontal appendages adapted for different feeding modes, compound eyes on stalks, and prominent head carapaces. Radiodonts inform on the paleoecology of early animal communities and the steps involved in euarthropod evolution. Four families within Radiodonta have been established. The raptorial predator families Anomalocarididae and Amplectobeluidae were dominant early in the evolutionary history of Radiodonta, but were later overtaken by the mega-diverse and widespread Hurdiidae, which has a more generalised sediment-sifting predatory mode. Suspension feeding, notably in the families Tamisiocarididae and Hurdiidae, also evolved at least twice in the history of the clade. The well-preserved anatomical features of the radiodont body and head have also provided insights into the evolution of characteristic features of Euarthropoda, such as the biramous limbs, compound eyes, and organisation of the head. With 37 species recovered from all major paleocontinents of the Cambrian and Early Ordovician, Radiodonta provides a unique opportunity for revealing evolutionary patterns during the Cambrian Explosion.
... , and Innovatiocaris bears no such endite. Anomalocarididae, which is represented by its type species Anomalocaris canadensis, have endites of its frontal appendages with auxiliary spines on both anterior and posterior margins A C C E P T E D M A N U S C R I P T (Daley and Edgecombe, 2014). Innovatiocaris differs from Anomalocarididae with no posterior auxiliary spines. ...
... With outer spines on only distalmost podomeres, endites alternating in size, absence of enlarged or hypertrophied endites, and no reduced distal podomeres, the general architecture of I. maotianshanensis frontal appendages is most compatible with those in non-hurdiids, especially Anomalocarididae (see Daley and Edgecombe, 2014). Nevertheless, the frontal appendage of I. maotianshanensis possesses homonomous endites on proximal podomeres of articulated region, as well as only anterior auxiliary spines and no posterior auxiliary ones on endites, such a combination of features is an important characteristic of Hurdiidae that is absent in non-hurdiid radiodonts (e.g., Daley . ...
... In I. maotianshanensis, the setal structures are situated on the dorsal side of trunk flaps, but they are not connected in the axial body region. This character state is consistent with the paired setal structures in An. canadensis (Daley and Edgecombe, 2014) and Am. symbrachiata (Chen et al., 1994). ...
The Palaeozoic radiodonts are important for understanding the evolution and ecology of early euarthropods. However, complete radiodont fossils are very rare, despite their central roles in understanding radiodont palaeobiology. Here we describe Innovatiocaris maotianshanensis gen. et sp. nov. in detail based on an iconic complete radiodont specimen from the early Cambrian Chengjiang Lagerstätte of China. The head of I . maotianshanensis has a pair of stalked eyes, an ovate dorsal sclerite, a pair of frontal appendages composed of 11 distal articulated podomeres bearing spiky endites with only anterior auxiliary spines, and a putative triradial oral cone. The body possesses six anterior pairs of small differentiated neck flaps and ten posterior pairs of trunk flaps, with soft tissues including alimentary canal and musculature preserved. The tail includes a tail fan comprising three pairs of lateral blades and a pair of very long furcae. Another two new species, Innovatiocaris ? sp. and I .? multispiniformis sp. nov., are established based on the frontal appendages with different numbers of anterior auxiliary spines and are tentatively assigned to Innovatiocaris . Phylogenetic analysis retrieves Innovatiocaris as either a basal member of Hurdiidae or early-branching species of the non-hurdiid clade. Thus, Innovatiocaris provides new insights into the radiodont phylogeny and illuminates the early diversification of Radiodonta.
Supplementary material: Supplementary figures, phylogenetic data matrix, and a character list for phylogenetic analysis are available at https://doi.org/10.6084/m9.figshare.c.6179300
Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/topic/collections/advances-in-the-cambrian-explosion
... Radiodonts, among the largest marine nektonic animals during the Early Paleozoic, have been generally regarded as the Earth's oldest apex predators (e.g., Whittington and Briggs, 1985;Briggs, 1994;Chen et al., 1994;Daley and Edgecombe, 2014;Liu et al., 2018;Paterson et al., 2020). Members of this group that includes the emblematic Anomalocaris, diversified over 500 million years ago, and have provided crucial insights into the early evolution and radiation of Euarthropoda (Daley et al., 2009;Van Roy et al., 2015a). ...
... Lower stem-group euarthropods such as radiodonts have helped to polarize the sequence of acquisition and identify homologous structures in stem representatives of fundamental euarthropod characters, such as arthropodized appendages, compound eyes, dorsal head sclerotization, and the biramous limb (Daley et al., 2009;Cong et al., 2014;Ortega-Hernández, 2015;Van Roy et al., 2015a;Edgecombe, 2020;Paterson et al., 2020). Members of this clade are characterized by a single pair of spiny arthropodized frontal appendages, a ventrally directed mouth surrounded by radial mouthparts composed of plates of multiple sizes that form a highly-cohesive structure, large compound eyes, dorsoventrally flattened body with one or two series of lateral imbricating flaps and usually a tail fan (Whittington and Briggs, 1985;Daley et al., 2009;Daley and Edgecombe, 2014;Van Roy et al., 2015a;Liu et al., 2018;Caron, 2019, 2022;Caron and Moysiuk, 2021;Pates et al., 2021a). Four families are known, primarily distinguished by the morphology of their frontal appendages: Amplectobeluidae, Anomalocarididae, Hurdiidae, and Tamisiocarididae (e.g., Daley and Budd, 2010;Vinther et al., 2014;Van Roy et al., 2015a;Lerosey-Aubril and Pates, 2018;Liu et al., 2018;Wu et al., 2021b). ...
... Four families are known, primarily distinguished by the morphology of their frontal appendages: Amplectobeluidae, Anomalocarididae, Hurdiidae, and Tamisiocarididae (e.g., Daley and Budd, 2010;Vinther et al., 2014;Van Roy et al., 2015a;Lerosey-Aubril and Pates, 2018;Liu et al., 2018;Wu et al., 2021b). Frontal appendage morphology also has ecological implications: amplectobeluids and anomalocaridids have flexible appendages with robust thorny endites suited to raptorial predation (Chen et al., 1994;Daley and Edgecombe, 2014;Liu et al., 2018), while hurdiids and tamisiocaridids likely utilized sediment sifting and suspension-feeding modes, facilitated by more elongate endites (Daley et al., 2013a;Vinther et al., 2014;Van Roy et al., 2015a;Lerosey-Aubril and Pates, 2018;Moysiuk and Caron, 2019;Wu et al., 2021b). ...
Over one hundred of arthropod fossil species have been described from the famous Chengjiang Lagerstätte (South China, Cambrian Stage 3, ca. 518 Ma) including a diverse assemblage of radiodonts – a group containing Anomalocaris and its relatives. These iconic stem-group euarthropods include some of the largest animals of the time, and some are known from hundreds of specimens. A longstanding conundrum has been the rarity or absence of hurdiids from Cambrian Series 2 Lagerstätten like Chengjiang. This is because radiodonts are generally common in such deposits and the oldest radiodont ever discovered is a hurdiid. Furthermore, this family displays the widest geographic and temporal ranges of all radiodont families, and the highest diversity. Here we document the first hurdiid frontal appendages from Chengjiang, which display unique features within the family and may provide insights for understanding the character evolution of hurdiid appendages. The palaeoenvironmental distribution of hurdiids suggests that the rarity of hurdiids in Chengjiang may be due to a preference for deeper water environments, and the later success of this family from the Wuliuan onwards may relate to their ability to tolerate cooler water temperatures than other radiodont families. The palaeogeographical, palaeoenvironmental, and stratigraphical patterns observed in hurdiids maybe caused in part by the limited distributions of Konservat-Lagerstätten in the Cambrian as well.
... Two of the most peculiar Burgess Shale animals, Anomalocaris and Opabinia, illustrate the complicated history of research of many Cambrian soft-bodied taxa-a result of their unfamiliar morphologies compared to the occupants of modern oceans [4][5][6]. Both Anomalocaris and Opabinia possess compound eyes, lateral swimming flaps, filamentous setal structures and a tail fan [7][8][9][10]. Anomalocaris and its relatives, the radiodonts, are united by the presence of paired sclerotized protocerebral frontal appendages and mouthparts composed of plates of multiple sizes, forming a diverse group containing over 20 species quarry in the Burgess Shale. ...
... The slender, broadly rectangular dorsal outline of the body in U. comosa is comparable to what is observed in both O. regalis and the radiodonts Aegirocassis benmoulae and Hurdia spp. This outline contrasts with the diamond-like outline of many radiodonts, including Amplectobelua symbrachiata, Anomalocaris canadensis and Peytoia nathorsti [8,10,57]. In addition, both O. regalis and radiodonts possess setal blades, in varying arrangements (electronic supplementary material, figure S1). ...
... The body is prolonged posteriorly by an unpaired and non-serrated structure in An. canadensis, Kerygmachela kierkegaardi, and Schinderhannes bartelsi (e.g. [10,19,31]), which may represent fused caudal rami or alternatively, a non-appendicular tail spine. Regardless, all these unpaired terminal structures are much longer relative to the main body than the caudal rami of opabiniids, and none exhibit serrated margins. ...
Once considered 'weird wonders' of the Cambrian, the emblematic Burgess Shale animals Anomalocaris and Opabinia are now recognized as lower stem-group euarthropods and have provided crucial data for constraining the polarity of key morphological characters in the group. Anomalocaris and its relatives (radiodonts) had worldwide distribution and survived until at least the Devonian. However, despite intense study, Opabinia remains the only formally described opabiniid to date. Here we reinterpret a fossil from the Wheeler Formation of Utah as a new opabiniid, Utaurora comosa nov. gen. et sp. By visualizing the sample of phylogenetic topologies in tree-space, our results fortify support for the position of U. comosa beyond the nodal support traditionally applied. Our phylogenetic evidence expands opabiniids to multiple Cambrian stages. Our results underscore the power of treespace visualization for resolving imperfectly preserved fossils and expanding the known diversity and spatio-temporal ranges within the euarthropod lower stem group.
... [39]). Radiodonts are the earliest diverging stem-group euarthropods with arthropodized appendages [5,49,50], and they were among the largest animals in Cambrian oceans, ranging from millimetres to around a metre in length (e.g. [51,52]). ...
... Endites similar in size (relative to the size of the appendage) and shape (triangular) to those of Lihuacaris can also be found in the Burgess Shale amplectobeluid Amplectobelua stephenensis and representatives of Caryosyntrips, a radiodont genus of three species recovered from deposits in Spain and North America [49,[57][58][59]. Lastly, the putative extensor muscle of Lihuacaris passes through the same part of the appendage (close to the dorsal margin) and is similar in size and curvature to the 'diffuse band' described from Anomalocaris canadensis frontal appendages [50]. However, other aspects of the organization of Lihuacaris appendages preclude a radiodont affinity. ...
... Indeed, various radiodonts display a monosegmented shaft comparable to Lihuacaris ferox (e.g. Anomalocaris canadensis; 'Anomalocaris' briggsi; Peytoia nathorsti; Caryosyntrips serratus [49,50,60,61]), though multisegmented shafts are also known (e.g. Houcaris saron; Laminacaris chimera; Ramskoeldia platyacantha [36,62,63]; but see [64] for an alternative view). ...
Stem-group euarthropods are important for understanding the early evolutionary and ecological history of the most species-rich animal phylum on Earth. Of particular interest are fossil taxa that occupy a phylogenetic position immediately crownwards of radiodonts, for this part of the euarthropod tree is associated with the appearance of several morphological features that characterize extant members of the group. Here, we report two new euarthropods from the Cambrian Stage 4 Guanshan Biota of South China. The fuxianhuiid Alacaris? sp. is represented by isolated appendages composed of a gnathobasic protopodite and an endite-bearing endopod of at least 20 podomeres. This material represents the youngest occurrence of the family Chengjiangocarididae, and its first record outside the Chengjiang and Xiaoshiba biotas. We also describe Lihuacaris ferox gen. et sp. nov. based on well-preserved and robust isolated appendages. Lihuacaris ferox exhibits an atypical combination of characters including an enlarged rectangular base, 11 endite-bearing podomeres and a hypertrophied distal element bearing 8–10 curved spines. Alacaris? sp. appendages display adaptations for macrophagy. Lihuacaris ferox appendages resemble the frontal appendages of radiodonts, as well as the post-oral endopods of chengjiangocaridid fuxianhuids and other deuteropods with well-documented raptorial/predatory habits. Lihuacaris ferox contributes towards the record of endemic biodiversity in the Guanshan Biota.
... Various hypotheses have been proposed to explain the functional roles radiodont feeding structures may have served (frontal appendages and mouth apparatus), but none have been tested. Anomalocaris canadensis is generally thought to have been a stealthy macro predator [2,13,20,21,31] that grasped large prey, while the appendages of Hurdia victoria and Peytoia nathorsti have been proposed to have worked as a jaw or sieve to prior shift sediment [21,32,33]. The amplectobeluid appendage is posed to have functioned as grasping/ cutting pincers and Cambroraster falcatus has been interpreted as sediment sifter as well [20,21,[31][32][33][34][35][36], while the delicate accessory spines/bristles in members of the tamisiocaridae and Aegirocassis and Pahvantia served in filter-feeding. ...
... Anomalocaris canadensis is generally thought to have been a stealthy macro predator [2,13,20,21,31] that grasped large prey, while the appendages of Hurdia victoria and Peytoia nathorsti have been proposed to have worked as a jaw or sieve to prior shift sediment [21,32,33]. The amplectobeluid appendage is posed to have functioned as grasping/ cutting pincers and Cambroraster falcatus has been interpreted as sediment sifter as well [20,21,[31][32][33][34][35][36], while the delicate accessory spines/bristles in members of the tamisiocaridae and Aegirocassis and Pahvantia served in filter-feeding. Radiodonts lack compelling modern analogues as they possess only a single pair of feeding appendages. ...
... In articulated specimens, appendages are occasionally found with the ventral surface facing the other appendage. This might indicate synchronized movements, although a single appendage might have been sufficient to firmly grab prey (see electronic supplementary material, video S1) [31]. The internal diameter of the space created by a minimally flexed appendage able to grab an object is 20-28% of the total appendage dorsal length. ...
Radiodonts evolved to become the largest nektonic predators in the Cambrian period persisting into the Ordovician and perhaps up until the Devonian period. They used a pair of large frontal appendages together with a radial mouth apparatus to capture and manipulate their prey and had evolved a range of species with distinct appendage morphologies already by the Early Cambrian (approx. 521 Ma). However, since their discovery, there has been a lack of understanding about their basic functional anatomy and thus their ecology. To explore radiodont modes of feeding, we have digitally modelled different appendage morphologies represented by Anomalocaris canadensis, Hurdia victoria, Peytoia nathorsti, Amplectobelua stephenensis and Cambroraster falcatus from the Burgess Shale. Our results corroborate ideas that there was likely a significant functional and, hence, behavioural diversity among different radiodont species with adaptations for feeding on differently sized prey (0.07 cm up to 10 cm). We argue here that Cambroraster falcatus appendages were suited for feeding on suspended particles rather than filtering sediment. Given the limited dexterity and lack of accessory feeding appendages as seen in modern arthropods, feeding must have been inefficient and ‘messy’, which may explain their subsequent replacement by crown group arthropods, cephalopods and jawed vertebrates.
... The frontal appendages attached adjacent to the ventral oral cone anteriorly, and were used for feeding following different strategies. These strategies include prey capture (e.g., Daley and Budd 2010;Daley and Edgecombe 2014;Liu et al. 2018), sediment sifting (e.g., Daley et al. 2013a;Moysiuk and Caron 2019) and even suspension feeding (e.g., Vinther et al. 2014;Van Roy et al. 2015; Lerosey-Aubril and . The frontal appendages consist of a series of well-sclerotized podomeres, sepa-rated from one another by arthrodial membranes, and carrying endites of varied morphologies. ...
... The terminology for isolated radiodont appendages follows the terms used by Daley and Edgecombe (2014) and Guo et al. (2019). The proximal-most podomeres of the frontal appendage are referred to as the "shaft". ...
... In most amplectobeluids, the endite is distinctively longer on the fifth podomere than the third-as seen in a previously described specimen of this taxon fig. 1g) -while in Anomalocarididae the endite is longer on the third than the fifth (e.g., Daley and Edgecombe 2014). Vinther et al. (2014) referred "Anomalocaris" kunmingensis as Amplectobelua kunmingensis, but more recent studies have simply treated this taxon as either Anomalocaris kunmingensis or "Anomalocaris" kunmingensis (e.g., Cong et al. 2014;Van Roy et al. 2015;Lerosey-Aubril and Pates 2018;Liu et al. 2018;Zeng et al. 2018a;Guo et al. 2019;Lerosey-Aubril et al. 2020). ...
The Guanshan Biota (South China, Cambrian, Stage 4) contains a diverse assemblage of biomineralizing and non-biomineralizing animals. Sitting temporally between the Stage 3 Chengjiang and Wuliuan Kaili Biotas, the Guanshan Biota contains numerous fossil organisms that are exclusive to this exceptional deposit. The Guanshan Konservat-Lagerstätte is also unusual amongst Cambrian strata that preserve non-biomineralized material, as it was deposited in a relatively shallow water setting. In this contribution we double the diversity of radiodonts known from the Guanshan Biota from two to four, and describe the second species of Paranomalocaris. In addition, we report the first tamisiocaridid from South China, and confirm the presence of a tetraradial oral cone bearing small and large plates in “Anomalocaris” kunmingensis, the most abundant radiodont from the deposit. All four radiodont species, and three genera, are apparently endemic to the Guanshan Biota. When considered in the wider context of geographically and temporally comparable radiodont faunas, endemism in Guanshan radiodonts is most likely a consequence of the shallower and more proximal environment in which they lived. The strong coupling of free-swimming radiodonts and benthic communities underlines the complex relationship between the palaeobiogeographic and environmental distributions of prey and predators. This local adaptation of radiodonts to their prey is highlighted by the frontal appendage morphology of the two species of Paranomalocaris, apparently specialised to different feeding modes, while the recognition of the limited geographic range of some radiodont faunas highlights the importance of exploring as many deposits as possible to fully understand this group.
... Recent elaboration of the head structure of Amplectobula has shown that somewhat similar structures were also present in this taxon (Cong et al., 2017). In addition, the thorough redescription of Anomalocaris canadensis by Daley and Edgecombe (2014) has demonstrated that a rather large circular and rimmed dorsal sclerite was also present, and on the basis of this they thus discarded the concept of a ventral hypostome-like sclerite being present in the radiodontids, a position that was discussed and affirmed by Ortega-Hern andez (2015). Furthermore, the probable broad distribution of the P-elements amongst the radiodontids has recently been argued for by Moysiuk and Caron (2019b), including in A. canadensis. ...
... In support of this view of the presence of a separate dorsal sclerite in this specimen, it should be noted that this is how the dorsal sclerite is sometimes preserved in A. canadensis as well (see e.g., fig. 8 of Daley and Edgecombe, 2014). ...
... This can be compared to the larger circular dorsal sclerite known from A. canadensis that covers most of head (see e.g., fig. 17 of Daley and Edgecombe, 2014), which is also apparently present in P. nathorsti too. The head structure of A. saron is discussed at length by Zeng et al. (2018), who also illustrate new material. ...
A widely (although not universally) accepted model of arthropod head evolution postulates that the labrum, a structure seen in almost all living euarthropods, evolved from an anterior pair of appendages homologous to the frontal appendages of onychophorans. However, the implications of this model for the interpretation of fossil arthropods have not been fully integrated into reconstructions of the euarthropod stem group, which remains in a state of some disorder. Here I review the evidence for the nature and evolution of the labrum from living taxa, and reconsider how fossils should be interpreted in the light of this. Identification of the segmental identity of head appendage in fossil arthropods remains problematic, and often rests ultimately on unproven assertions. New evidence from the Cambrian stem-group euarthropod Parapeytoia is presented to suggest that an originally protocerebral appendage persisted well up into the upper stem-group of the euarthropods, which prompts a re-evaluation of widely-accepted segmental homologies and the interpretation of fossil central nervous systems. Only a protocerebral brain was implicitly present in a large part of the euarthropod stem group, and the deutocerebrum must have been a relatively late addition.
... Two of the most peculiar Burgess Shale animals, Anomalocaris and Opabinia, illustrate the complicated history of research of many Cambrian soft-bodied taxa -a result of their unfamiliar morphologies compared to the occupants of modern oceans Briggs, 2015b). Both Anomalocaris and Opabinia possess compound eyes, lateral swimming flaps, filamentous setal structures, and a tail fan Whittington and Briggs, 1985;Budd and Daley, 2012;Daley and Edgecombe, 2014). Recent work has revealed that Anomalocaris and its relatives, the radiodonts, are united by the presence of paired sclerotized protocerebral frontal appendages and mouthparts composed of plates of multiple sizes, forming a diverse group containing over 20 taxa Cong et al., 2014;Vinther et al., 2014;Ortega-Hernández, Janssen and Budd, 2017;Liu et al., 2018;Moysiuk and Caron, 2019). ...
... The slender, broadly rectangular dorsal outline of the body in KUMIP 314087 is comparable to what is observed in both Opabinia and the radiodonts Aegirocassis and Hurdia. This outline contrasts with the diamond-like outline of many radiodonts, including Amplectobelua symbrachiata, Anomalocaris canadensis, and Peytoia nathorsti (Whittington and Briggs, 1985;Chen, Ramsköld and Zhou, 1994;Daley and Edgecombe, 2014). In addition, both Opabinia and radiodonts possess setal blades, in varying arrangements (Supplementary Fig. 1). ...
... A tail fan associated with caudal rami is also known in both Opabinia and some radiodonts, though the number of blades known in KUMIP 314087 (at least seven, likely eight, on each side) by far exceeds what is known in either Opabinia (three) or any radiodont (ranging from zero to three). The acuminate tips of elongate caudal blades of KUMIP 314087 are most similar in morphology to those of Anomalocaris, and contrast to the more lobate caudal structures known in Opabinia and other radiodonts such as Hurdia (Fig. 2) Chen, Ramsköld and Zhou, 1994;Daley, Budd and Caron, 2013;Daley and Edgecombe, 2014). Paired caudal rami are also known in Anomalocaris saron, though these are much more elongate than in both KUMIP 314087 and Opabinia and lack the serrated adaxial margin common to the opabiniid taxa ( Fig. 2) Chen, Ramsköld and Zhou, 1994). ...
Once considered ‘weird wonders’ of the Cambrian, the emblematic Burgess Shale animals Anomalocaris and Opabinia are now recognized as lower stem-group euarthropods. Anomalocaris and its relatives (radiodonts) had a worldwide distribution and survived until at least the Devonian, whereas - despite intense study - Opabinia remains the only formally described opabiniid to date. Here we reinterpret a fossil from the Wheeler Formation of Utah as a new opabiniid, KUMIP 314087. By visualizing the sample of phylogenetic topologies in treespace, our results fortify support for the position of KUMIP 314087 beyond the nodal support traditionally applied. Our phylogenetic evidence expands opabiniids to multiple Cambrian Stages spanning approximately five million years. Our results underscore the power of treespace visualization for resolving imperfectly preserved fossils and expanding the known diversity and spatiotemporal ranges within the euarthropod lower stem group.
Additional note
This work contains a new biological name. New names in preprints are not considered available by the ICZN. To avoid ambiguity, the new biological name is not included in this preprint, and the specimen number (KUMIP 314087) is used as a placeholder.
Abstract Figure
Cover image. Artistic reconstruction of the new opabiniid from the Wheeler Formation, Utah, USA (Cambrian: Drumian). Artwork by F. Anthony.
... , a clade of stem-group euarthropods, have been generally regarded as fearsome apex predators in Palaeozoic marine ecosystem (e.g. Whittington and Briggs, 1985;Briggs, 1994;Chen et al., 1994;Paterson et al., 2011;Daley et al., 2013b;Daley and Edgecombe, 2014;Liu et al., 2018). The group is typified by paired arthropodised frontal appendages that attach adjacent to radial mouthparts, large compound eyes, a sophisticated digestive system and lateral imbricating body flaps associated with setal blades. ...
... Unlike hurdiids and tamisiocaridids, the anomalocaridid and amplectobeluid endites are much shorter relative to the height of their attached podomeres, and possess less auxiliary spines (e.g. Daley and Edgecombe, 2014;Cong et al., 2017). Anomalocaridids can be confidently differentiated from amplectobeluids by the absence of single hypertrophied endite. ...
... Aria and Caron, 2015 has applied an analytical approach (morphospace) to include the radiodont frontal appendages in a quantitative characterization of morphological breadth, demonstrating their large disparity (more comprehensive endeavor has also been presented by Zeng et al., 2018). The considerable morphological variation of frontal appendages indicates that radiodonts occupied several niches in Cambrian ecosystems, including roles as raptorial predators (Chen et al., 1994;Daley and Budd, 2010;Daley and Edgecombe, 2014;Liu et al., 2018), sediment sifters (Daley et al., 2013a;Moysiuk and Caron, 2019) and suspension feeders (Daley et al., 2013b;Vinther et al., 2014;Van Roy et al., 2015;Lerosey-Aubril and Pates, 2018). ...
Radiodonts are a morphologically and ecologically diverse clade of stem-group euarthropods that occupied numerous ecological niches in early animal ecosystems. Many Cambrian taxa are considered apex predators, primarily due to the possession of raptorial frontal appendage, though sweep and filter-feeding examples were also prevalent. Four major families have been distinguished including Anomalocarididae, whose elongate appendages consist of a series of podomeres bearing short endites. Studies of anomalocaridids have seen limited investigation in the Chengjiang Lagerstätte (Cambrian Stage 3) of China, despite the deposit being well-known for the diverse radiodont assemblage, and recently the putative anomalocaridid ‘Anomalocaris’ saron was reassigned to Tamisiocarididae. Here we present exceptionally preserved specimens of two new anomalocaridid taxa from Chengjiang. Lenisicaris lupata gen. et sp. nov. represents the first valid Chengjiang anomalocaridid taxon, characterized by bearing short endites lacking auxiliary spines on almost all its podomeres. A second taxon, Anomalocaris cf. canadensis Whiteaves, 1892, indicates a broad geographical range for this famous Burgess Shale species. With the help of this new information, we show that the family Anomalocarididae was widespread at low latitudes from Cambrian Stage 4 to the Guzhangian. The biogeographical patterns of anomalocaridids suggest a high dispersal capability in the larval form of anomalocaridids, and possible climatic control on their distribution. Furthermore, the known distribution of anomalocaridids in the well-documented soft-bodied biotas indicates that anomalocaridids were likely adapted to a broad spectrum of environments.
... Radiodonts-a diverse extinct group that includes Anomalocaris and its relativeshave long been known as comparatively common elements in Cambrian Konservat-Lagerstätten, but an ever-growing body of evidence shows that these organisms occupied a variety of ecological niches and contributed in different ways to the diversity of early animal communities (Daley & Budd, 2010;Daley & Edgecombe, 2014;Vinther et al., 2014;Van Roy, Daley & Briggs, 2015;Lerosey-Aubril & Pates, 2018;Liu et al., 2018;Moysiuk & Caron, 2019). Radiodonts greatly differed in size, ranging from millimetres to meters in length (Van Roy, Daley & Briggs, 2015;Lerosey-Aubril & Pates, 2018;Liu et al., 2018;Pates et al., 2020a), and had variable body shapes that impacted their swimming capabilities. ...
... Radiodonts are typically reconstructed as nektonic animals (also referred to as 'free swimmers' hereafter), with the possible exception of the eudemersal Cambroraster (Moysiuk & Caron, 2019;Liu et al., 2020). Forms with elongate swimming flaps and reduced cephalic sclerites (amplectobeluids and anomalocaridids; Daley & Edgecombe, 2014;Cong et al., 2014Cong et al., , 2016Cong et al., , 2017Cong et al., , 2018Liu et al., 2018) were likely more agile swimmers than those with comparatively reduced, but paired flaps, and cylindrical bodies made semi-rigid by the presence of an elongate cephalic carapace (e.g. the hurdiids Aegirocassis and Hurdia; Daley et al., 2009;Daley, Budd & Caron, 2013; Van Roy, Daley & Briggs, 2015). Swimming power has been shown to increase with the size of swimming flaps (Usami, 2006), which are more developed in amplectobeluids and anomalocaridids. ...
... This term is equivalent to 'enditic spines' of Moysiuk & Caron (2019). We follow the terminology of Liu et al. (2020) for cephalic carapace elements, Daley & Edgecombe (2014) for trunk parts, and Daley & Bergström (2012) for components of the oral cone, with the addition of the term 'tooth' (used in Daley, Budd & Caron (2013) and Zeng et al. (2018)) to describe spines protruding from the inner margins of oral cone plates. Additional terminology relating to the orientation and measurements of Caryosyntrips frontal appendages follows . ...
Radiodonts have long been known from Cambrian deposits preserving non-biomineralizing organisms. In Utah, the presence of these panarthropods in the Spence and Wheeler (House Range and Drum Mountains) biotas is now well-documented. Conversely, radiodont occurrences in the Marjum Formation have remained scarce. Despite the large amount of work undertaken on its diverse fauna, only one radiodont (Peytoia) has been reported from the Marjum Biota. In this contribution we quadruple the known radiodont diversity of the Marjum fauna, with the description of the youngest members of two genera, Caryosyntrips and Pahvantia, and that of a new taxon Buccaspinea cooperi gen. et sp. nov. This new taxon can be identified from its large oral cone bearing robust hooked teeth with one, two, or three cusps, and by the unique endite morphology and organisation of its frontal appendages. Appendages of at least 12 podomeres bear six recurved plate-like endites proximal to up to four spiniform distal endites. Pahvantia hastata specimens from the Marjum Formation are particularly large, but otherwise morphologically indistinguishable from the carapace elements of this species found in the Wheeler Formation. One of the two new Caryosyntrips specimens can be confidently assigned to C. camurus. The other bears the largest spines relative to appendage length recorded for this genus, and possesses endites of variable size and unequal spacing, making its taxonomic assignment uncertain. Caryosyntrips, Pahvantia, and Peytoia are all known from the underlying Wheeler Formation, whereas isolated appendages from the Spence Shale and the Wheeler Formation, previously assigned to Hurdia, are tentatively reidentified as Buccaspinea. Notably, none of these four genera occurs in the overlying Weeks Formation, providing supporting evidence of a faunal restructuring around the Drumian-Guzhangian boundary. The description of three additional nektonic taxa from the Marjum Formation further documents the higher relative proportion of free-swimming species in this biota compared to those of the Wheeler and Weeks Lagerstätten. This could be related to a moderate deepening of the basin and/or changing regional ocean circulation at this time.
... Radiodonts-a diverse extinct group that includes Anomalocaris and its relativeshave long been known as comparatively common elements in Cambrian Konservat-Lagerstätten, but an ever-growing body of evidence shows that these organisms occupied a variety of ecological niches and contributed in different ways to the diversity of early animal communities (Daley & Budd, 2010;Daley & Edgecombe, 2014;Vinther et al., 2014;Van Roy, Daley & Briggs, 2015;Lerosey-Aubril & Pates, 2018;Liu et al., 2018;Moysiuk & Caron, 2019). Radiodonts greatly differed in size, ranging from millimetres to meters in length (Van Roy, Daley & Briggs, 2015;Lerosey-Aubril & Pates, 2018;Liu et al., 2018;Pates et al., 2020a), and had variable body shapes that impacted their swimming capabilities. ...
... Radiodonts are typically reconstructed as nektonic animals (also referred to as 'free swimmers' hereafter), with the possible exception of the eudemersal Cambroraster (Moysiuk & Caron, 2019;Liu et al., 2020). Forms with elongate swimming flaps and reduced cephalic sclerites (amplectobeluids and anomalocaridids; Daley & Edgecombe, 2014;Cong et al., 2014Cong et al., , 2016Cong et al., , 2017Cong et al., , 2018Liu et al., 2018) were likely more agile swimmers than those with comparatively reduced, but paired flaps, and cylindrical bodies made semi-rigid by the presence of an elongate cephalic carapace (e.g. the hurdiids Aegirocassis and Hurdia; Daley et al., 2009;Daley, Budd & Caron, 2013; Van Roy, Daley & Briggs, 2015). Swimming power has been shown to increase with the size of swimming flaps (Usami, 2006), which are more developed in amplectobeluids and anomalocaridids. ...
... This term is equivalent to 'enditic spines' of Moysiuk & Caron (2019). We follow the terminology of Liu et al. (2020) for cephalic carapace elements, Daley & Edgecombe (2014) for trunk parts, and Daley & Bergström (2012) for components of the oral cone, with the addition of the term 'tooth' (used in Daley, Budd & Caron (2013) and Zeng et al. (2018)) to describe spines protruding from the inner margins of oral cone plates. Additional terminology relating to the orientation and measurements of Caryosyntrips frontal appendages follows . ...
Radiodonts have long been known from Cambrian deposits preserving non-biomineralizing organisms. In Utah, the presence of these panarthropods in the Spence and Wheeler (House Range and Drum Mountains) biotas is now well-documented. Conversely, radiodont occurrences in the Marjum Formation have remained scarce. Despite the large amount of work undertaken on its diverse fauna, only one radiodont (Peytoia) has been reported from the Marjum Biota. In this contribution we quadruple the known radiodont diversity of the Marjum fauna, with the description of the youngest members of two genera, Caryosyntrips and Pahvantia, and that of a new taxon Buccaspinea cooperi gen. et sp. nov. This new taxon can be identified from its large oral cone bearing robust hooked teeth with one, two, or three cusps, and by the unique endite morphology and organisation of its frontal appendages. Appendages of at least 12 podomeres bear six recurved plate-like endites proximal to up to four spiniform distal endites. Pahvantia hastata specimens from the Marjum Formation are particularly large, but otherwise morphologically indistinguishable from the carapace elements of this species found in the Wheeler Formation. One of the two new Caryosyntrips specimens can be confidently assigned to C. camurus. The other bears the largest spines relative to appendage length recorded for this genus, and possesses endites of variable size and unequal spacing, making its taxonomic assignment uncertain. Caryosyntrips, Pahvantia, and Peytoia are all known from the underlying Wheeler Formation, whereas isolated appendages from the Spence Shale and the Wheeler Formation, previously assigned to Hurdia, are tentatively reidentified as Buccaspinea. Notably, none of these four genera occurs in the overlying Weeks Formation, providing supporting evidence of a faunal restructuring around the Drumian-Guzhangian boundary. The description of three additional nektonic taxa from the Marjum Formation further documents the higher relative proportion of free-swimming species in this biota compared to those of the Wheeler and Weeks Lagerstätten. This could be related to a moderate deepening of the basin and/or changing regional ocean circulation at this time.
... The radiodont head also features a range of sclerites or carapace elements that have only come to light in the past 15 years (15). These include separate dorsal and lateral cephalic plates [as in Anomalocaris (10,16), Amplectobelua (13), and Lyrarapax (6)], an integrated carapace composed of dorsal and lateral elements [as in Hurdia (17)], or in one unusual example, an expanded, horseshoeshaped carapace [as in Cambroraster (10,18,19)]. ...
... In contrast to the surge in knowledge of the radiodont head structures listed above, much less is known about the eyes. Although a pair of stalked eyes has been recognized in several different radiodont genera (1,2,4,6,10,15,16), only outlines were available until the preserved visual surface was revealed in Anomalocaris from the Emu Bay Shale (Cambrian Series 2, Stage 4) of South Australia (20). Each stalked eye of Anomalocaris is pyriform, with a visual surface showing a huge number of ommatidial lenses arranged with the hexagonal packing typical of euarthropod compound eyes. ...
... A medial head sclerite and paired lateral sclerites occur, for example, in Amplectobelua symbrachiata (13); in this species, some previously identified eyes (28) were reinterpreted as P-elements (13). Likewise, in A. canadensis, which also has a dorsomedial head sclerite (16), structures that had been previously identified as eyes in some specimens were reinterpreted as P-elements (10). The case for homology between the eye sclerite of 'A.' briggsi and the lateral sclerites of L. unguispinus (and possibly A. symbrachiata and A. canadensis) is supported by their close association with the eye. ...
Radiodonts are nektonic stem-group euarthropods that played various trophic roles in Paleozoic marine ecosystems, but information on their vision is limited. Optical details exist only in one species from the Cambrian Emu Bay Shale of Australia, here assigned to Anomalocaris aff. canadensis . We identify another type of radiodont compound eye from this deposit, belonging to ‘ Anomalocaris ’ briggsi . This ≤4-cm sessile eye has >13,000 lenses and a dorsally oriented acute zone. In both taxa, lenses were added marginally and increased in size and number throughout development, as in many crown-group euarthropods. Both species’ eyes conform to their inferred lifestyles: The macrophagous predator A. aff. canadensis has acute stalked eyes (>24,000 lenses each) adapted for hunting in well-lit waters, whereas the suspension-feeding ‘ A. ’ briggsi could detect plankton in dim down-welling light. Radiodont eyes further demonstrate the group’s anatomical and ecological diversity and reinforce the crucial role of vision in early animal ecosystems.
... 2b,d,f,i,. These appendages share key morphological features of the radiodont families Anomalocarididae and Amplectobeluidae represented by Anomalocaris 12 and Ramskoeldia 13 , respectively ('fa' in Fig. 2d, detailed comparisons are provided in the Supplementary Discussion). Their shared similarities include 12-15 distal articulated podomeres 2g and Extended Data Figs. ...
... 1d,e,2b,f,i,5b), endites of alternating lengths ('se ' and 'ed' in Figs. 1c,, e, 2b, i, 4a, d-i) and roughly symmetrically arranged auxiliary spines on each endite (arrowheads in Fig. 2e, f, h, i); we also infer a similar functional morphology 12,13 (Fig. 2d,. However, in contrast to radiodonts, the upward orientation and the absence of outer spines in the frontalmost appendages of Kylinxia ('fa' in Figs. ...
... A synapomorphy in Hallucigenia. 12. Integumental sclerites, size change along body axis: (0) close; (1) A feature in artiopodans. ...
Resolving the early evolution of euarthropods is one of the most challenging problems in metazoan evolution1,2. Exceptionally preserved fossils from the Cambrian period have contributed important palaeontological data to deciphering this evolutionary process3,4. Phylogenetic studies have resolved Radiodonta (also known as anomalocaridids) as the closest group to all euarthropods that have frontalmost appendages on the second head segment (Deuteropoda)5–9. However, the interrelationships among major Cambrian euarthropod groups remain disputed1,2,4,7, which impedes our understanding of the evolutionary gap between Radiodonta and Deuteropoda. Here we describe Kylinxia zhangi gen. et. sp. nov., a euarthropod from the early Cambrian Chengjiang biota of China. Kylinxia possesses not only deuteropod characteristics such as a fused head shield, a fully arthrodized trunk and jointed endopodites, but also five eyes (as in Opabinia) as well as radiodont-like raptorial frontalmost appendages. Our phylogenetic reconstruction recovers Kylinxia as a transitional taxon that bridges Radiodonta and Deuteropoda. The most basal deuteropods are retrieved as a paraphyletic lineage that features plesiomorphic raptorial frontalmost appendages and includes Kylinxia, megacheirans, panchelicerates, ‘great-appendage’ bivalved euarthropods and isoxyids. This phylogenetic topology supports the idea that the radiodont and megacheiran frontalmost appendages are homologous, that the chelicerae of Chelicerata originated from megacheiran great appendages and that the sensorial antennae in Mandibulata derived from ancestral raptorial forms. Kylinxia thus provides important insights into the phylogenetic relationships among early euarthropods, the evolutionary transformations and disparity of frontalmost appendages, and the origin of crucial evolutionary innovations in this clade.
... Most of the extinct marine megafauna taxa are identified to species level (93%). The earliest marine megafauna species are the 1-m-long Anomalocaris canadensis and Amplectobelua symbrachiata from the Cambrian (Cong et al., 2017;Daley and Budd, 2010;Daley and Edgecombe, 2014; Figure 1). The largest size attained by any extinct marine megafauna sampled was 21 m by Shonisaurus sikanniensis, an oceanic, pelagic, macropredatory ichthyosaur from the Upper Triassic (Nicholls and Manabe, 2004; Figure 1). ...
... During the Cambrian, only two taxa were found to be categorised as megafauna following our definition: A. canadensis and A. symbrachiata, both reaching 1 m (Figures 1 and 4B; Cong et al., 2017;Daley and Budd, 2010;Daley and Edgecombe, 2014). During the Ordovician, the maximum body size for the entire Palaeozoic is reached ( Figure 4B) with the possibly up to 9 m long nautiloid Endoceras giganteum (Klug et al., 2015). ...
The modern marine megafauna is known to play important ecological roles and includes many charismatic species that have drawn the attention of both the scientific community and the public. However, the extinct marine megafauna has never been assessed as a whole, nor has it been defined in deep time. Here, we review the literature to define and list the species that constitute the extinct marine megafauna, and to explore biological and ecological patterns throughout the Phanerozoic. We propose a size cut-off of 1 m of length to define the extinct marine megafauna. Based on this definition, we list 706 taxa belonging to eight main groups. We found that the extinct marine megafauna was conspicuous over the Phanerozoic and ubiquitous across all geological eras and periods, with the Mesozoic, especially the Cretaceous, having the greatest number of taxa. Marine reptiles include the largest size recorded (21 m; Shonisaurus sikanniensis ) and contain the highest number of extinct marine megafaunal taxa. This contrasts with today’s assemblage, where marine animals achieve sizes of >30 m. The extinct marine megafaunal taxa were found to be well-represented in the Paleobiology Database, but not better sampled than their smaller counterparts. Among the extinct marine megafauna, there appears to be an overall increase in body size through time. Most extinct megafaunal taxa were inferred to be macropredators preferentially living in coastal environments. Across the Phanerozoic, megafaunal species had similar extinction risks as smaller species, in stark contrast to modern oceans where the large species are most affected by human perturbations. Our work represents a first step towards a better understanding of the marine megafauna that lived in the geological past. However, more work is required to expand our list of taxa and their traits so that we can obtain a more complete picture of their ecology and evolution.
... This hypothesis can explain the rare occurrence of complete organisms belonging to taxa such as radiodonts in the Walcott Quarry (Daley et al., 2009(Daley et al., , 2013. Though radiodonts are diverse in the Burgess Shale, complete carcasses, such as the nektonic predator Anomalocaris, are extremely rare, and fossils mainly represent molting products or decomposed carcasses (Daley et al., 2009(Daley et al., , 2013Daley and Edgecombe, 2014). Hurdia is thought to swim close to the seafloor and is ten times more abundant at this locality than Anomalocaris (Daley et al., 2009(Daley et al., , 2013Daley and Budd, 2010;Daley and Edgecombe, 2014). ...
... Though radiodonts are diverse in the Burgess Shale, complete carcasses, such as the nektonic predator Anomalocaris, are extremely rare, and fossils mainly represent molting products or decomposed carcasses (Daley et al., 2009(Daley et al., , 2013Daley and Edgecombe, 2014). Hurdia is thought to swim close to the seafloor and is ten times more abundant at this locality than Anomalocaris (Daley et al., 2009(Daley et al., , 2013Daley and Budd, 2010;Daley and Edgecombe, 2014). Molting products and carcasses fall to the seafloor and are passively transported by sediment gravity flows to the preservation site (Fig. 2c), and taxa living low in the water column have less chance of escaping the incoming sediment gravity flow. ...
Understanding the functioning of extinct ecosystems is a complicated knot of ecological, evolutionary, and preservational strands that must be untangled. For instance, anatomical and behavioral differences can profoundly alter fossilization pathways. This is particularly true in exceptionally preserved soft-bodied biotas that record the earliest phases of animal evolution during the Cambrian Explosion and the Ordovician Radiation. Herein, a novel method of data partitioning based on probabilistic modelling is developed to examine these processes for the Walcott Quarry, Burgess Shale, Canada (510Ma), and the Fezouata Shale, Morocco (c. 475Ma). The modelling shows that the mechanism for soft-tissue preservation in the Walcott Quarry is ecologically selective, favoring the endobenthos. This is not found in the Fezouata Shale. Taken in concert with bioturbation data, a new model of comparative preservation is developed based on sedimentary flow dynamics. This suggests that during the Cambrian Explosion and Ordovician Radiation the most exceptional fossils sites must still be calibrated against each other to understand the unfolding evolutionary events and the ecological structuring of ancient animal communities.
... Nonappendicular fossil discoveries may be critical to resolving this issue. The gnathites of Stanleycaris also resemble the endites of Anomalocaris canadensis in their trident-like shape (Daley and Edgecombe 2014); however, they are set apart by their curvature and attachment along the outermedial rather than the inner margin of the appendage. In curvature, the gnathites of Stanleycaris more closely resemble the toothed margins of the oral cone, which could point to functional similarities (see "Functional Implications"). ...
... The most compelling case for a multipodomerous peduncle comes from Amplectobelua symbrachiata (Cong et al. 2017), but even here the expression of the putative boundaries is somewhat variable. In other species, the peduncle is either composed of a single podomere (Daley et al. 2013b;Daley and Edgecombe 2014; or we consider the number to be ambiguous (Cong et al. 2016Guo et al. 2018). Thus, in the phylogenetic scenario in which the first two podomeres in the Stanleycaris appendage represent the peduncle, this subdivision would likely have to be interpreted as an autapomorphy. ...
Radiodonts (stem Euarthropoda) were ecologically diverse, but species generally displayed limited functional specialization of appendages along the body axis compared with crown group euarthropods. This is puzzling, because such functional specialization is considered to have been an important driver of euarthropod ecological diversification. One way to circumvent this constraint could have been the functional specialization of different parts of the frontal appendages, known to have been ecologically important in radiodonts. This hypothesis has yet to be tested explicitly. Here we redescribe the poorly known mid-Cambrian hurdiid radiodont Stanleycaris hirpex from the Burgess Shale (Stephen Formation) and quantitatively assess functional specialization of the frontal appendages of stem euarthropods. The appendages of Stanleycaris are composed of 14 podomeres, variously differentiated by their possession of pectinate endites, mono- to trifurcate medial gnathites, and outer spines. The oral cone is tetraradially organized and can be uniquely distinguished from those of other hurdiids by the presence of 28 rather than 32 smooth tridentate plates. Our phylogenetic analysis finds Stanleycaris in a grade of hurdiids retaining plesiomorphic raptorial appendicular functionality alongside derived adaptations for sweep feeding and large, bilaterally opposed gnathites. We conclude that the latter performed a masticatory function, convergent with gnathal structures like mandibles in various panarthropods. Taken together, Stanleycaris and similar hurdiids provide an extreme example of the evolution of division of labor within the appendage of a stem euarthropod and suggest that this innovation may have facilitated the functional transition, from raptorial to sweep feeding, at the origin of the hurdiid clade.
... This hypothesis can explain the rare occurrence of complete organisms belonging to taxa such as radiodonts in the Walcott Quarry (Daley et al., 2009(Daley et al., , 2013. Though radiodonts are diverse in the Burgess Shale, complete carcasses, such as the nektonic predator Anomalocaris, are extremely rare, and fossils mainly represent molting products or decomposed carcasses (Daley et al., 2009(Daley et al., , 2013Daley and Edgecombe, 2014). Hurdia is thought to swim close to the seafloor and is ten times more abundant at this locality than Anomalocaris (Daley et al., 2009(Daley et al., , 2013Daley and Budd, 2010;Daley and Edgecombe, 2014). ...
... Though radiodonts are diverse in the Burgess Shale, complete carcasses, such as the nektonic predator Anomalocaris, are extremely rare, and fossils mainly represent molting products or decomposed carcasses (Daley et al., 2009(Daley et al., , 2013Daley and Edgecombe, 2014). Hurdia is thought to swim close to the seafloor and is ten times more abundant at this locality than Anomalocaris (Daley et al., 2009(Daley et al., , 2013Daley and Budd, 2010;Daley and Edgecombe, 2014). Molting products and carcasses fall to the seafloor and are passively transported by sediment gravity flows to the preservation site (Fig. 2c), and taxa living low in the water column have less chance of escaping the incoming sediment gravity flow. ...
... Cambrian arthropods bearing elongate frontal appendages with multi-annulated elements, referred to as "great appendages" have a long research history [1][2][3]. Besides the famous Radiodonta including anomalocarids [4][5][6] and hurdiids [7,8], another group is known to also include smaller euarthropods with the so-called "great appendages" with fewer elements-the Megacheira [9]. This group contains species that are assigned to Leanchoilia sp. ...
Background
The early Cambrian arthropod clade Megacheira, also referred to as great appendage arthropods, comprised a group of diminutive and elongated predators during the early Palaeozoic era, around 518 million years ago. In addition to those identified in the mid-Cambrian Burgess Shale biota, numerous species are documented in the renowned 518-million-year-old Chengjiang biota of South China. Notably, one species, Tanglangia longicaudata, has remained inadequately understood due to limited available material and technological constraints. In this study, we, for the first time, examined eight fossil specimens (six individuals) utilizing state-of-the-art μCT and computer-based 3D rendering techniques to unveil the hitherto hidden ventral and appendicular morphology of this species.
Results
We have identified a set of slender endopodites gradually narrowing distally, along with a leaf-shaped exopodite adorned with fringed setae along its margins, and a small putative exite attached to the basipodite. Our techniques have further revealed the presence of four pairs of biramous appendages in the head, aligning with the recently reported six-segmented head in other early euarthropods. Additionally, we have discerned two peduncle elements for the great appendage. These findings underscore that, despite the morphological diversity observed in early euarthropods, there exists similarity in appendicular morphology across various groups. In addition, we critically examine the existing literature on this taxon, disentangling previous mislabelings, mentions, descriptions, and, most importantly, illustrations.
Conclusions
The μCT-based investigation of fossil material of Tanglangia longicaudata, a distinctive early Cambrian euarthropod from the renowned Chengjiang biota, enhances our comprehensive understanding of the evolutionary morphology of the Megacheira. Its overall morphological features, including large cup-shaped eyes, raptorial great appendages, and a remarkably elongated telson, suggest its potential ecological role as a crepuscular predator and adept swimmer in turbid waters.
... Muchos de los restos de este género se encuentran en Konservat Lagerstätten y es por eso que se conservan varias pruebas de las partes blandas del cuerpo de Isoxys, como los ojos, las glándulas intestinales, endópodos, exópodos, etc. (Pates et al., 2021). Figura 1: reconstrucción de un Anomalocaris canadensis en vista dorsal, con un corte en el cuerpo que muestra estructuras internas (Daley & Edgecombe, 2014). ...
Palaeontology is dedicated to the scientific study of the past of life on Earth
through, among other elements, fossils. The fossils are found in several types of
deposits, and of these the Konservat Lagerstätten stand out, where there are
specimens preserved in exceptional conditions. The genus Isoxys is mainly
known thanks Cambrian to deposits of this nature spread all over the world:
China, Greenland, USA... In this period one of the most important biological
events in the history of the Earth took place: the Cambrian radiation. In this
radiation all the animal phyla that we currently have nowadays originated, and
some that have not been preserved to these days. The arthropods, a very
numerous phyla both now and then, are very interesting since there were animals
very different from those we find now. A curious group within the Cambrian
arthropods is that of the bivalve arthropods, to which Isoxys belonged. It had a
characteristic shell with two spines on the front and back each and a specific
pattern of ornamentation. It is known to inhabit well-lit waters and to have had a
cosmopolitan distribution, partially governed by temperature. It should be noted
that, in the Cambrian, there were no continents as we know them now, but there
was a super continent (Gondwana) and several continents scattered in the ocean
(Laurentia, Siberia...).
... This includes both Buccaspinea and Hurdia, the hurdiid radiodonts known from other material from Miners Hollow in the Spence Shale (described above), although the amplectobeluid Lyrarapax (only currently known from the Stage 3 Chengjiang in China) also bears only 11 podomeres in its distal articulated region (Cong et al., 2014(Cong et al., , 2016Liu et al., 2018). The putative dorsal spines lack the size and recurved nature common for distal podomeres of amplectobeluid and anomalocaridid radiodonts (e.g., Amplectobelua stephenensis Daley and Budd, 2010, Anomalocaris canadensis Whiteaves, 1892; see Daley and Budd, 2010;Daley and Edgecombe, 2014), however this could be accounted for by their poor preservation. The strong curvature or the appendage distally is also observed in both amplectobeluid and hurdiid appendages. ...
The Cambrian (Miaolingian; Wuliuan) Spence Shale Lagerstätte of northern Utah and southern Idaho is one of the most diverse Burgess Shale-type deposits of Laurentia. It yields a diverse fauna consisting of abundant biomineralized and locally abundant soft-bodied fossils,along a range of environments from shallow water carbonates to deep shelf dark shales. Panarthropods are the dominant component throughout the deposit, both in time and space, but while the trilobites and agnostoids are abundant, most of the soft-bodied taxa are only known from very few specimens. Additionally, the knowledge of the soft-bodied panarthropods is currently largely limited to locations in the Wellsville Mountains of northeastern Utah. This contribution describes 21 new soft-bodied panarthropods from six locations, including the first occurrences of soft-bodied panarthropods in the High-Creek, Smithfield Creek, Spence Gulch, and Two-Mile Canyon localities. Additionally, we report the presence of bradoriids, Branchiocaris pretiosa, Perspicaris? dilatus, Naraoia? sp., Thelxiope cf. T. palaeothalassia, and Tuzoia guntheri for the first time from the Spence Shale Lagerstätte, the first occurrence reported outside of the Burgess Shale for Thelxiope cf. T. palaeothalassia and the first Wuliuan occurrence of Tuzoia guntheri. We also report on a new hurdiid carapace element and additional specimens of Buccaspinea cooperi?, Dioxycaris argenta, Hurdia sp., and Tuzoia retifera. This new material improves our understanding of the panarthropod fauna of the Spence Shale Lagerstätte and substantially increases our understanding of the distribution of the described taxa in time and space.
... Stem-euarthropods such as opabiniids [76], several radiodonts (e.g. Anomalocaris [77]) and some isoxyids [21,69] are characterized by a tail fan composed of multiple pairs of blade-like tail flukes. This condition is not present among euarthropods but it is worth noting that radiodonts were not restricted to this specific condition either, and show widely different types of tail flukes (e.g. ...
The origin of mandibulates, the hyperdiverse arthropod group that includes pancrustaceans and myriapods, dates back to the Cambrian. Bivalved arthropod groups such as hymenocarines have been argued to be early mandibulates, but many species are still poorly known, and their affinities remain uncertain. One of the most common and globally distributed Cambrian bivalved arthropods is Tuzoia . Originally described in 1912 from the Burgess Shale based on isolated carapaces, its full anatomy has remained largely unknown. Here, we describe new specimens of Tuzoia from the Canadian Burgess Shale (Wuliuan, Cambrian) showcasing exceptionally preserved soft tissues, allowing for the first comprehensive reconstruction of its anatomy, ecology and evolutionary affinities. The head bears antennae and differentiated cephalic appendages. The body is divided into a cephalothorax, a homonomous trunk bearing ca 10 pairs of legs with heptopodomerous endopods and enlarged basipods, and a tail fan with two pairs of caudal rami. These traits suggest that Tuzoia swam along the seafloor and used its spinose legs for predation or scavenging. Tuzoia is retrieved by a Bayesian phylogenetic analysis as an early mandibulate hymenocarine lineage, exemplifying the rapid diversification of this group in open marine environments during the Cambrian Explosion.
... As the name implies, these animals are typically characterized by a ring-like mouth, or an oral cone. This structure is not unique to radiodonts, and may even be absent in some taxa (Cong et al., 2016;Cong et al., 2018), but when present, the radiodont oral cone is characterized by a series of plates with individual elements of different sizes (Daley and Bergström 2012;Daley and Edgecombe, 2014;Liu et al., 2018;Moysiuk and Caron 2021). Radiodonts also have a pair of large and sometimes raptorial frontal appendages, and a series of flaps along the body which are presumed to have been used for swimming (Usami, 2006). ...
Parvibellus atavus gen. et sp. nov. from the Early Cambrian Chengjiang fauna of China is a small fossil having a distinct cephalic region bearing a pair of lateral projections and a circular, ventral mouth. The trunk bears eleven pairs of probably flap-like appendages and a short pair of terminal projections. This character combination is unique for the Chengjiang biota. A circular ventral mouth is seen in Radiodonta and in some of the gilled lobopodians which are thought to be among the radiodont’s closest relatives. P. atavus, gilled lobopodians, opabiniids, and radiodonts also share the putative character of flap-like appendages along the trunk. However, the new fossil differs from radiodonts and gilled lobopodians by the absence of enlarged and/or raptorial frontal appendages. It also differs from gilled lobopodians by lacking in ventral lobopod limbs and from radiodonts by lacking in stalked eyes. It provisionally resolves as a sister-group to a clade containing the gilled lobopodians, opabiniids, and radiodonts, and could potentially be part of an early radiation of the nektonic lower stem—Euarthropoda.
... Some ancestral arthropods lack any gnathal appendages (Daley et al. 2009;Legg et al. 2012;Daley and Edgecombe 2014), and others are equipped with basipodites with small spines (Legg 2014; or gnathobasic appendages (Stein 2013;Caron 2017b, 2019; Bicknell et al. 2018;Yang et al. 2018;Zhai et al. 2019c;Jiao et al. 2021). Ancestral mandibulates, having a pair of specialized gnathal appendages on the post-tritocerebral segment, emerged by the end of the Cambrian period (Zhang et al. 2007), and the mandible is one of the apomorphic characteristics of a monophyletic clade composed of Pancrustacea and Myriapoda (Rota-Stabelli et al. 2011, 2013. ...
Arthropods with a pair of mandibles (Mandibulata) emerged by the end of the Cambrian period. The mandible is one of the apomorphic characteristics of this monophyletic clade, which is composed of Pancrustacea and Myriapoda. Acquisition of the mandible is one of the important events of the evolutionary pathway of arthropods because the powerful masticatory system provides benefits to individuals regarding food selection. Ancestral mandibulates are well known as so-called Cambrian bivalved arthropods, and a few of them provide a pair of valid mandibles with a broad molar process. However, extant bivalved arthropods can only be found in a few lineages of crustaceans, though all of them are equipped with mandibles. This study focuses on the neuroanatomy of the mandibular skeleto-muscular system of Heterocypris incongruens (Ostracoda, Crustacea), a millimeter-sized bivalved crustacean. Electron microscopy reveals that numerous mechanoreceptive sensilla are distributed inside the mandibular gnathal edges and that there are two types (heterodynal and monodynal) of sensilla, which differ in the number of dendrites and their probable function. This sensory nervous system in the gnathal edges contributes to the precise interdigitation of the right and left mandibles to allow for powerful omnivorous mastication, and the mandibular interdigitation plays a role as the fulcrum of triggering action to open the valves. Therefore, by reversing its fulcrum and load, the mandibular skeleto-muscular system in podocopid ostracods has two sub-systems with different functions, namely the "mandibular masticatory system" and the "valve opening system." Furthermore, this investigation provides significant information on the feeding mode of Cambrian bivalved arthropods, from the view of the functional morphology of the mandibular skeleto-muscular system.
... The putative setose endites described by Lerosey-Aubril and Pates [22] are more comparable to structures interpreted as gill blades, associated with flaps or body segments in anomalocaridids and hurdiids [4,12,15] including Hurdia (figure 6e-h). These bands of lamellate structures are not part of an appendage, nor are they likely to have been used for feeding (contra [22]), probably functioning instead for respiration [15]. ...
Radiodonts, stem-group euarthropods that evolved during the Cambrian explosion, were among the largest and most diversified lower palaeozoic predators. These animals were widespread geographically, occupying a variety of ecological niches, from benthic foragers to nektonic suspension feeders and apex predators. Here, we describe the largest Cambrian hurdiid radiodont known so far, Titanokorys gainesi , gen. et sp. nov., from the Burgess Shale (Marble Canyon, Kootenay National Park, British Columbia). Estimated to reach half a metre in length, this new species bears a very large ovoid-shaped central carapace with distinct short posterolateral processes and an anterior spine. Geometric morphometric analyses highlight the high diversity of carapace shapes in hurdiids and show that Titanokorys bridges a morphological gap between forms with long and short carapaces. Carapace shape, however, is prone to homoplasy and shows no consistent relationship with trophic ecology, as demonstrated by new data, including a reappraisal of the poorly known Pahvantia . Despite distinct carapaces, Titanokorys shares similar rake-like appendages for sediment-sifting with Cambroraster, a smaller but much more abundant sympatric hurdiid from the Burgess Shale . The co-occurrence of these two species on the same bedding planes highlights potential competition for benthic resources and the high diversity of large predators sustained by Cambrian communities.
... is a clade of stem arthropods (sensu Ortega-Hernandez 2016) that have generally been regarded as large apex predators of the Cambrian and Ordovician Periods (e.g. Briggs 1994;Chen et al. 1994;Whittington and Briggs 1985;Daley and Budd 2010;Paterson et al. 2011;Daley et al. 2013a, b;Daley and Edgecombe 2014;Van Roy et al. 2015;Liu et al. 2018). These animals are typified by paired grasping frontal appendages with a series of morphologically diverse endites, radial mouthparts, prominent dorsolateral compound eyes on stalks, a series of flexible lateral flaps along its dorsoventrally flattened body and tail fans. ...
Radiodonts were cosmopolitan and diverse stem-euarthropods that have been generally regarded as the apex Cambrian predators. Four major groups have been distinguished including tamisiocaridids, primarily based on the endite features of the frontal appendages. Anomalocaris saron Hou, Bergström and Ahlberg, 1995, one of the most well-known radiodonts in the Chengjiang Lagerstätte, is generally treated as a member of the Family Anomalocarididae. New anatomical evidence reported here, allied with the data of microcomputed tomography (CT) shows that the endites in A. saron are paired, much longer than the height of associated podomeres, and furnished with multiple slender distal auxiliary spines. These new observations allow us to reassign A. saron to a new genus, Houcaris gen. nov., and strongly support its tamisiocaridid affinities rather than anomalocaridid as previously suggested. Houcaris saron thus represents the first tamisiocaridid species known from South China, as well as the oldest tamisiocaridid in the fossil record (Cambrian Stage 3). Our occurrence data, coupled with other distribution of tamisiocaridids, demonstrates that this group is restricted to the early Cambrian (Series 2), and occur across South China, Laurentia and eastern Gondwana within tropics/subtropics belt, indicating a possible climatic control on their distribution. Moreover, these tamisiocaridid records documented in several Konservat Lagerstätten suggest an ecological preference to shallow water environment with well-oxygenated sea bottom conditions.
... The peculiar morphology of Luancaia could also draw comparisons with the ventral organization of some lower stem-group euarthropods (see Ortega-Hernández, 2016), which are typified by the presence of lobopodous trunk limbs, and in general lack other sclerotized hard parts on most of the body. The sub-quadrate lateral impressions of Luancaia are somewhat reminiscent of the segmentally repeated lateral body flaps observed in numerous species of gilled lobopodians (e.g., Kerygmachela, Pambdelurion, Opabinia; see Whittington, 1975;Budd, 1993Budd, , 1996Budd, , 1998Budd, , 1999Park et al., 2018) and radiodonts (e.g., Anomalocaris, Aegirocassis, Hurdia; see Daley and Budd, 2010;Daley and Edgecombe, 2014;Van Roy et al., 2015). In this case, the body flaps consist of nonsclerotized paired appendages that were supported by a hydrostatic skeleton, and occasionally reinforced by internal rod-like strengthening rays, and which were employed for swimming through synchronized movement. ...
Luancaia igen. Nov. and its two new ichnospecies, L. candasensis and L. elongata, from the Middle Devonian Naranco Formation of Asturias, northern Spain, record infaunal moulting most likely related to a defensive strategy. The new ichnogenus has an elongate to oblong outline, and displays a distinctly trilobate appearance that includes an axial longitudinal lobe characterized by a distinctive ridge flanked by lateral lobes at each side. Well-defined transverse ridges convey a metameric-like appearance consisting of up to nine distinct segments. The anterior-most part is more variable, but consistently features a pair of oval strongly convex, or a subtriangular fan-like ridge in well-preserved specimens.
Luancaia is similar to Rusophycus in its general segmented appearance, suggesting a euarthropod producer, but differs in the presence of a distinctive axial ridge and in the absence of scratch imprints. Luancaia closely resembles the dorsal side of the enigmatic Carboniferous oniscid-like euarthropod Camptophyllia. We propose that Luancaia records supine (i.e. upside-down) infaunal moulting of a euarthropod with a dorsal exoskeletal morphology similar to Camptophyllia, in which exuviation was facilitated by dorsal anchoring on a firm muddy substrate.
The Naranco Formation records sedimentation in a shallow- and marginal-marine setting that at times was affected by fluvial discharge most likely during storm floods. In particular, Luancaia is preserved in storm-flood beds that accumulated in relative proximity to a river mouth. These latter deposits consist of sparsely bioturbated sandstone and mudstone that reflect deposition under stressful conditions, such as salinity stress, high sedimentation rate, and turbidity. By burrowing into the sediment, the producer avoided the stressed physical conditions of the sediment surface. Marginal-marine settings, where competition and predation pressures were significantly lower than in adjacent fully marine environments, may have served as safe moulting sites during the mid-Paleozoic marine radiation.
... nov. has a large pygidium with paired short falcate spines and a terminal tailspine ( Figure 3A); Kiisortoqia has a small tail shield with neither spines nor a tailspine and twice the number of thoracic tergites; see Figure 4B and also Stein, 2010, p. 482-483, figures 4B, 5B-C); (2) trilobation of thoracic tergites effaced; (3) dorsal spine is present on each podomere of the frontal head limb (see Daley and Edgecombe, 2014). Type material. ...
Bushizheia yangi gen. et sp. nov. is a euarthropod species from the Cambrian (Series 2, Stage 3) Chengjiang Lagerstätte, Southwest China. Sclerotised dorsal terg-ites, sclerotisation of post-frontal head limb appendages, and no isolated cephalic sclerite support the euarthropod affinities of B. yangi gen. et sp. nov. However, the frontal head limbs resemble in morphology the anteroventral raptorial appendage of radi-odonts. Although, due to the absence of critical soft anatomy, we cannot elucidate the exact segmental affinities of these raptorial appendages, the possession of ‘great appendage’-like frontal head limbs is important for assessing the range of limb morphology evolved by early euarthropods.
... Amplectobelua symbrachiata; [10]); anomalocaridids (e.g. Anomalocaris canadensis; [11]); and tamisiocaridids (e.g. Tamisiocaris borealis; [31]). ...
Originally considered as large, solely Cambrian apex predators, Radiodonta—a clade of stem-group euarthropods including Anomalocaris—now comprises a diverse group of predators, sediment sifters and filter feeders. These animals are only known from deposits preserving non-biomineralized material, with radiodonts often the first and/or only taxa known from such deposits. Despite the widespread and diverse nature of the group, only a handful of radiodonts are known from postCambrian deposits, and all originate from deposits or localities rich in other total-group euarthropods. In this contribution, we describe the first radiodont from the UK, an isolated hurdiid frontal appendage from the Tremadocian (Lower Ordovician) Dol-cyn-Afon Formation, Wales, UK. This finding is unusual in two major aspects: firstly, the appendage (1.8 mm in size) is
less than half the size of the next smallest radiodont frontal appendage known, and probably belonged to an animal between 6 and 15 mm in length; secondly, it was discovered in the sponge-dominated Afon Gam Biota, one of only a handful
of non-biomineralized total-group euarthropods known from this deposit. This Welsh hurdiid breaks new ground for Radiodonta in terms of both its small size and spongedominated habitat. This occurrence demonstrates the adaptability of the group in response to the partitioning of ecosystems and environments in the late Cambrian and Early Ordovician world.
... Radiodonts are lower stem-group euarthropods (sensu Ortega-Hernández, 2016; see Daley et al. 2009;Cong et al. 2014;Vinther et al. 2014;Van Roy et al. 2015;Lerosey-Aubril & Pates 2018;Moysiuk & Caron, 2019) characterized by a sclerotization of the body wall that is restricted to a few elements of the head region, namely the frontal appendages and discrete cephalic sclerites. For decades, these animals were depicted as the fearsome apex-predators of the Early Palaeozoic seas, as best incarnated by the Burgess Shale taxon Anomalocaris (Whittington & Briggs, 1985;Chen et al. 1994;Vannier & Chen, 2005;Daley et al. 2013a;Daley & Edgecombe, 2014). However, in recent years it has become clear that radiodonts were a taxonomically and ecologically diverse group, which played a key role in the emergence of complex marine trophic webs. ...
Radiodonts are a diverse clade of Lower Palaeozoic stem-group euarthropods that played a key role in the emergence of complex marine trophic webs. The latest addition to the group, Cambroraster falcatus, was recently described from the Wuliuan Burgess Shale, and is characterized by a unique horseshoe-shaped central carapace element. Here we report the discovery of Cambroraster sp. nov. A, a new species from the Cambrian Stage 3 Chengjiang Lagerstätte of South China. The new occurrence of Cambroraster demonstrates that some of the earliest known radiodonts had already evolved a highly derived carapace morphology adapted to an essentially eudemersal life as sediment foragers.
Almost fifteen years have passed since the printing of the first volume in the Italian language published by the Back to the Past Museum.
Encouraged by its success in Italy and abroad, we decided to publish the translated version in English the following year (The Back to the Past Museum Guide to TRILOBITES). This tome, enlarged with updated plates, became a best seller in the paleontological field, obtaining an important worldwide distribution and a particularly positive evaluation by the professional sector.
This overwhelmingly positive response allowed our project to continuously expand the museum’s collections. Additionally, we began implementing research campaigns (always respecting international rules and laws), started an intense collaboration with professionals in the field, and consequently, have published in high-impact scientific journals.
This new volume, compared to the previous one, has not only been enriched with new tables and iconographic sources but it has also been updated regarding the classification of trilobite orders in accordance with the latest interpretations and studies. Studies that will lead to new interpretations and, consequently, new reorganizations of families and genera within the class of trilobites.
What we hope is that this text will attract the interest of the “warned” collector, the professional or simply the passionate. We would also like to dedicate this work of ours to each one of them, in the hope of reinforcing the thin bridge that exists between public and private, both interdependent for study, field research, the discovery of new species and the evolution of scientific thought.
Animal colour vision is based on comparing signals from different photoreceptors. It is generally assumed that processing different spectral types of photoreceptor mainly serves colour vision. Here I propose instead that photoreceptors are parallel feature channels that differentially support visual-motor programmes like motion vision behaviours, prey capture and predator evasion. Colour vision may have emerged as a secondary benefit of these circuits, which originally helped aquatic vertebrates to visually navigate and segment their underwater world. Specifically, I suggest that ancestral vertebrate vision was built around three main systems, including a high-resolution general purpose greyscale system based on ancestral red cones and rods to mediate visual body stabilization and navigation, a high-sensitivity specialized foreground system based on ancestral ultraviolet cones to mediate threat detection and prey capture, and a net-suppressive system based on ancestral green and blue cones for regulating red/rod and ultraviolet circuits. This ancestral strategy probably still underpins vision today, and different vertebrate lineages have since adapted their original photoreceptor circuits to suit their diverse visual ecologies.
Lobopodians are an iconic and diverse group of animals from the Cambrian, which alongside radiodonts, present an important window into the evolution of arthropods and the development of Paleozoic ecosystems. Of these, a rare few species outside of Radiodonta possess lateral swimming flaps. The recent discovery of Utahnax provided much-needed insight into the evolution of swimming flaps, suggesting that the ventrolateral flaps of Kerygmachela evolved independently from other flap-bearing lobopodians and radiodonts. Here a new pelagic lobopodian species is described, Mobulavermis adustus new genus new species, the first lobopodian to be reported from the Cambrian-age Pioche Shale of Nevada. Mobulavermis adustus was large and possessed more ventrolateral flap pairs than any other known lobopodian or radiodont. It is found to be a close relative of both Kerygmachela and Utahnax , allowing the establishment of the new lobopodian family Kerygmachelidae new family. In addition, an indeterminate euarthropod fossil from the Pioche Formation is described in brief, and the recently described Chengjiang species Parvibellus avatus Liu et al., 2022, thought to have been related to the “gilled lobopodians,” is reinterpreted as a juvenile siberiid lobopodian.
UUID: http://zoobank.org/759c4eb9-ec60-4d5a-8b20-4f115ab79575
The stem-group euarthropod Anomalocaris canadensis is one of the largest Cambrian animals and is often considered the quintessential apex predator of its time. This radiodont is commonly interpreted as a demersal hunter, responsible for inflicting injuries seen in benthic trilobites. However, controversy surrounds the ability of A. canadensis to use its spinose frontal appendages to masticate or even manipulate biomineralized prey. Here, we apply a new integrative computational approach, combining three-dimensional digital modelling, kinematics, finite-element analysis (FEA) and computational fluid dynamics (CFD) to rigorously analyse an A. canadensis feeding appendage and test its morphofunctional limits. These models corroborate a raptorial function, but expose inconsistencies with a capacity for durophagy. In particular, FEA results show that certain parts of the appendage would have experienced high degrees of plastic deformation, especially at the endites, the points of impact with prey. The CFD results demonstrate that outstretched appendages produced low drag and hence represented the optimal orientation for speed, permitting acceleration bursts to capture prey. These data, when combined with evidence regarding the functional morphology of its oral cone, eyes, body flaps and tail fan, suggest that A. canadensis was an agile nektonic predator that fed on soft-bodied animals swimming in a well-lit water column above the benthos. The lifestyle of A. canadensis and that of other radiodonts, including plausible durophages, suggests that niche partitioning across this clade influenced the dynamics of Cambrian food webs, impacting on a diverse array of organisms at different sizes, tiers and trophic levels.
The relative sizes of body segments are a major determinant of shape and functionality of an animal. Developmental biases affecting this trait can therefore have major evolutionary implications. In vertebrates, a molecular activator/inhibitor mechanism, known as the inhibitory cascade (IC), produces a simple and predictable pattern of linear relative size along successive segments. The IC model is considered the default mode of vertebrate segment development and has produced long-term biases in the evolution of serially homologous structures like teeth, vertebrae, limbs and digits. Here we investigate whether the IC model or an IC-like model also has controls on segment size development in an ancient and hyper-diverse group of extinct arthropods, the trilobites. We examined segment size patterning in 128 trilobite species, and during ontogenetic growth in three trilobite species. Linear relative segment size patterning is prominent throughout the trunk of trilobites in the adult form and there is strict regulation of this patterning in newly developing segments in the pygidium. Extending the analysis to select stem and modern arthropods suggests the IC is a common default mode of segment development capable of producing long-term biases in morphological evolution across arthropods as it does in vertebrates.
Radiodonta, an extinct stem-euarthropod group, has been considered as the largest predator of Cambrian marine ecosystems. As one of the radiodont-bearing Konservat-Lagerstätten, the Guanshan biota (South China, Cambrian Stage 4) has yielded a diverse assemblage of soft-bodied and biomineralized taxa that are exclusive to this exceptional deposit. "Anomalocaris" kunmingensis, the most abundant radiodont in the Guanshan biota, was originally assigned to Anomalocaris within the Anomalocarididae. Despite this taxon being formally assigned to the family Amplectobeluidae more recently, its generic assignment remains uncertain. Here, we present new materials of "Anomalocaris" kunmingensis from the Guanshan biota, and reveal that the frontal appendages possess two enlarged endites; all endites bear one posterior auxiliary spine and up to four anterior auxiliary spines; three robust dorsal spines and one terminal spine protrude from the distal part. These new observations, allied with anatomical features illustrated by previous studies, allow us to assign this taxon to a new genus, Guanshancaris gen. nov. Brachiopod shell bearing embayed injury and incomplete trilobites, associated with frontal appendages in our specimens, to some extent confirm Guanshancaris as a possible durophagous predator. The distribution of amplectobeluids demonstrates that this group is restricted to Cambrian Stage 3 to Drumian, and occurs across South China and Laurentia within the tropics/subtropics belt. Moreover, the amount and abundance of amplectobeluids evidently decreases after the Early-Middle Cambrian boundary, which indicates its possible preference for shallow water, referring to its paleoenvironmental distribution and may be influenced by geochemical, tectonic, and climatic variation.
A crucial step in the evolution of Euarthropoda (chelicerates, myriapods, pancrustaceans) was the transition between fossil groups that possessed frontal appendages innervated by the first segment of the brain (protocerebrum), and living groups with a protocerebral labrum and paired appendages innervated by the second brain segment (deutocerebrum). Appendage homologies between the groups are controversial. Here we describe two specimens of opabiniid-like euarthropods, each bearing an anterior proboscis (a fused protocerebral appendage), from the Middle Ordovician Castle Bank Biota, Wales, UK. Phylogenetic analyses support a paraphyletic grade of stem-group euarthropods with fused protocerebral appendages and a posterior-facing mouth, as in the iconic Cambrian panarthropod Opabinia. These results suggest that the labrum may have reduced from an already-fused proboscis, rather than a pair of arthropodized appendages. If some shared features between the Castle Bank specimens and radiodonts are considered convergent rather than homologous, phylogenetic analyses retrieve them as opabiniids, substantially extending the geographic and temporal range of Opabiniidae. Here, the authors describe two opabiniid-like euarthropods with anterior proboscises from the Middle Ordovician Castle Bank Biota, Wales, UK. Phylogenetic analysis suggests that these specimens may be sister to radiodonts and deuteropods.
In addition to being among the most iconic and bizarre-looking Cambrian animals, radiodonts are a group that offers key insight into the acquisition of the arthropod body plan by virtue of their phylogenetic divergence prior to all living members of the phylum. Nonetheless, radiodont fossils are rare and often fragmentary, and contentions over their interpretation have hindered resolution of important evolutionary conundrums. Here, we describe 268 specimens of Stanleycaris hirpex from the Cambrian Burgess Shale, including many exceptionally preserved whole-body specimens, informing the most complete reconstruction of a radiodont to date. The trunk region of Stanleycaris has up to 17 segments plus two pairs of filiform caudal blades. The recognition of dorsal sclerotic segmentation of the trunk cuticle and putative unganglionated nerve cords provides new insight into the relative timing of acquisition of segmental traits, the epitome of the arthropod body plan. In addition to the pair of stalked lateral eyes, the short head unexpectedly bears a large median eye situated behind a preocular sclerite on an anteriorly projecting head lobe. Upon re-evaluation, similar median eyes can be identified in other Cambrian panarthropods demonstrating a deep evolutionary continuity. The exquisitely preserved brain of Stanleycaris is consistent with the hypothesized deutocerebral innervation of the frontal appendages, reconciling neuroanatomical evidence with external morphology in support of an ancestrally bipartite head and brain for arthropods. We propose that the integration of this bipartite head prior to the acquisition of most segmental characters exclusively in the arthropod trunk may help explain its developmental differentiation.
The origin of mandibulate arthropods can be traced back to the Cambrian period to several carapace-bearing arthropod groups, but their morphological diversity is still not well characterized. Here, we describe Balhuticaris voltae, a bivalved arthropod from the 506-million-year-old Burgess Shale (Marble Canyon, British Columbia, Canada). This species has an extremely elongated and multisegmented body bearing ca. 110 pairs of homonomous biramous limbs, the highest number among Cambrian arthropods, and, at 245 mm, it represents one of the largest Cambrian arthropods known. Its unusual carapace resembles an arch; it covers only the frontalmost section of the body but extends ventrally beyond the legs. Balhuticaris had a complex sensory system and was probably an active swimmer thanks to its powerful paddle-shaped exopods and a long and flexible body. Balhuticaris increases the ecological and functional diversity of bivalved arthropods and suggests that cases of gigantism occurred in more arthropod groups than previously recognized.
Arthropods are ubiquitous in all modern habitats and yet their origin remains poorly documented. It is widely thought that their segmented and arthrodized body evolved from the annulated vermiform body of a lobopodian ancestor c. 540 Ma. This major transformation included the evolution of sclerotized and articulated appendages from annulated nonjointed limbs or lobopods. However, this scenario is complicated by the presence in many stem-group arthropods of body flaps of various origins, characteristics and functions. We describe the new lobopodian Utahnax vannieri gen. et sp. nov. from Drumian strata of the House Range in Utah. Known from an incomplete specimen, this taxon features a vermiform, annulated body flanked by pairs of swimming flaps, except in the caudal region, and a digestive system with putative glands. Extensions of the body cavity into the body flaps of Utahnax suggest that they are modified lobopods similar to the ventral body flaps of radiodonts; as such, they are not homologous to the dorsal body flaps of the stem-group arthropods Opabinia, Pambdelurion, and possibly Kerygmachela. We discuss the details of the limb anatomy of these three taxa and consider an alternative interpretation for Kerygmachela. Despite morphological similarities in radiodonts, Utahnax, and possibly Kerygmachela, our parsimony and Bayesian inference phylogenetic analyses suggest that ventral body flaps have evolved convergently in those taxa, probably accompanying a shift towards a predominantly swimming predatory lifestyle. Ecological competition with radiodonts is proposed as an explanation for the scarcity of non-radiodont swimming lobopodians in Cambrian Lagerstätten.
The rise of arthropods is a decisive event in the history of life. Likely the first animals to have established themselves on land and in the air, arthropods have pervaded nearly all ecosystems and have become pillars of the planet's ecological networks. Forerunners of this saga, exceptionally well‐preserved Palaeozoic fossils recently discovered or re‐discovered using new approaches and techniques have elucidated the precocious appearance of extant lineages at the onset of the Cambrian explosion, and pointed to the critical role of the plankton and hard integuments in early arthropod diversification. The notion put forward at the beginning of the century that the acquisition of extant arthropod characters was stepwise and represented by the majority of Cambrian fossil taxa is being rewritten. Although some key traits leading to Euarthropoda are indeed well documented along a diversified phylogenetic stem, this stem led to several speciose and ecologically diverse radiations leaving descendants late into the Palaeozoic, and a large part, if not all of the Cambrian euarthropods can now be placed on either of the two extant lineages: Mandibulata and Chelicerata. These new observations and discoveries have altered our view on the nature and timing of the Cambrian explosion and clarified diagnostic characters at the origin of extant arthropods, but also raised new questions, especially with respect to cephalic plasticity. There is now strong evidence that early arthropods shared a homologous frontalmost appendage, coined here the cheira, which likely evolved into antennules and chelicerae, but other aspects, such as brain and labrum evolution, are still subject to active debate. The early evolution of panarthropods was generally driven by increased mastication and predation efficiency and sophistication, but a wealth of recent studies have also highlighted the prevalent role of suspension‐feeding, for which early panarthropods developed their own adaptive feedback through both specialized appendages and the diversification of small, morphologically differentiated larvae. In a context of general integumental differentiation and hardening across Cambrian metazoans, arthrodization of body and limbs notably prompted two diverging strategies of basipod differentiation, which arguably became founding criteria in the divergence of total‐groups Mandibulata and Chelicerata. The kinship of trilobites and their relatives remains a source of disagreement, but a recent topological solution, termed the ‘deep split’, could embed Artiopoda as sister taxa to chelicerates and constitute definitive support for Arachnomorpha. Although Cambrian fossils have been critical to all these findings, data of exceptional quality have also been accumulating from other Palaeozoic Konservat‐Lagerstätten, and a better integration of this information promises a much more complete and elaborate picture of early arthropod evolution in the near future. From the broader perspective of a total‐evidence approach to the understanding of life's history, and despite persisting systematic debates and new interpretative challenges, various advances based on palaeontological evidence open the prospect of finally using the full potential of the most diverse animal phylum to investigate macroevolutionary patterns and processes.
Correct interpretation of soft-bodied fossils relies on a thorough understanding of their taphonomy. While the focus has often been on the primary roles of decay and early diagenesis, the impacts of deeper burial and metamorphism on fossil preservation are less well understood. We document a sequence of late-stage mineral replacements in panarthropod fossils from the Sirius Passet Lagerstätte (North Greenland), an important early Cambrian Burgess Shale–type (BST) biota. Muscle and gut diverticula were initially stabilized by early diagenetic apatite, prior to being pervasively replaced by quartz and then subordinate chlorite, muscovite, and chloritoid during very low- to low-grade metamorphism. Each new mineral replicates the soft tissues with different precision and occurs in particular anatomical regions, imposing strong biases on the biological information retained. Muscovite and chloritoid largely obliterate the tissues’ original detail, suggesting that aluminum-rich protoliths may have least potential for conserving mineralized soft tissues in metamorphism. Overall, the fossils exhibit a marked shift toward mineralogical equilibration with the matrix, obscuring primary taphonomic modes. Sequential replacement of the phosphatized soft tissues released phosphorus to form new accessory monazite (and apatite and xenotime), whose presence in other BST biotas might signal the prior, more widespread, occurrence of this primary mode of preservation. Our results provide critical context for interpreting the Sirius Passet biota and for identifying late-stage overprints in other biotas.
The Furongian period represents an important gap in the fossil record of most groups of non-biomineralizing organisms, owing to a scarcity of Konservat-Lagerstätten of that age. The most significant of these deposits, the Jiangshanian strata of the Sandu Formation near Guole Township (Guangxi, South China), have yielded a moderately abundant, but taxonomically diverse soft-bodied fossil assemblage, which provides rare insights into the evolution of marine life at that time. In this contribution, we report the first discovery of a radiodont fossil from the Guole Konservat-Lagerstätte. The specimen is an incomplete frontal appendage of a possibly new representative of the family Hurdiidae. It is tentatively interpreted as composed of seven podomeres, six of which bearing laminiform endites. The best preserved of these endites is especially long, and it bears short auxiliary spines that greatly vary in size. This is the second occurrence of hurdiids and more generally radiodonts in the Furongian, the first being the external mould of an oral cone from Jiangshanian strata of the Wiśniówka Sandstone Formation in Poland. Restudy of this Polish specimen confirms that it belongs to a hurdiid radiodont and best compares to Peytoia. The family Hurdiidae includes the oldest (basal Cambrian Epoch 2) and youngest (Early Ordovician, possibly Early Devonian) representatives of the Radiodonta and as such, has the longest stratigraphical range of the group. Yet, hurdiids only became prominent components of marine ecosystems during the middle Cambrian (Miaolingian), and their fossil record in younger strata remains limited.
Background
The Chengjiang biota from southwest China (518-million-years old, early Cambrian) has yielded nearly 300 species, of which more than 80 species represent early chelicerates, crustaceans and relatives. The application of µCT-techniques combined with 3D software (e.g., Drishti), has been shown to be a powerful tool in revealing and analyzing 3D features of the Chengjiang euarthropods. In order to address several open questions that remained from previous studies on the morphology of the xandarellid euarthropod Sinoburius lunaris , we reinvestigated the µCT data with Amira to obtain a different approach of visualization and to generate new volume-rendered models. Furthermore, we used Blender to design 3D models showing aspects of intraspecific variation.
Results
New findings are: (1) antennulae consist of additional proximal articles that have not been detected before; (2) compared to other appendages, the second post-antennular appendage has a unique shape, and its endopod is comprised of only five articles (instead of seven); (3) the pygidium bears four pairs of appendages which are observed in all specimens. On the other hand, differences between specimens also have been detected. These include the presence/absence of diplotergites resulting in different numbers of post-antennular appendages and tergites and different distances between the tip of the hypostome and the anterior margin of the head shield.
Conclusions
Those new observations reveal intraspecific variation among Chengjiang euarthropods not observed before and encourage considerations about possible sexual dimorphic pairs or ontogenetic stages. Sinoburius lunaris is a variable species with respect to its morphological characters, cautioning that taxon-specific variabilities need to be considered when exploring new species.
Phylogenomics underpins a stable and mostly well-resolved hypothesis for the interrelationships of extant arthropods. Exceptionally preserved fossils are integrated into this framework by coding their morphological characters, as exemplified by total-evidence dating approaches that treat fossils as dated tips in analyses numerically dominated by molecular data. Cambrian fossils inform on the sequence of character acquisition in the arthropod stem group and in the stems of its main extant clades. The arthropod head problem incorporates unique appendage combinations and remains of the nervous system in fossils into a scheme mostly based on neuroanatomy and Hox expression domains for extant forms. Molecular estimates of arthropod origins in the Cryogenian or Ediacaran predate a coherent picture from the arthropod fossil record, which commences as trace fossils in the earliest Cambrian. Probabilistic morphological clock analysis of trilobites, which exemplify the earliest arthropod body fossils, supports a Cambrian origin, without the need to posit an unfossilized Ediacaran history.
Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 51 is November 2, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Biomineralised trilobite exoskeletons provide a 250 million year record of abnormalities in one of the most diverse arthropod groups in history. One type of abnormality-repaired injuries-have allowed palaeobiologists to document records of Paleozoic predation, accidental damage, and complications in moulting experienced by the group. Although Cambrian trilobite injuries are fairly well documented, the illustration of new injured specimens will produce a more complete understanding of Cambrian prey items. To align with this perspective, nine new abnormal specimens displaying healed injuries from the Smithsonian National Museum of Natural History collection are documented. The injury pattern conforms to the suggestion of lateralised prey defence or predator preference, but it is highlighted that the root cause for such patterns is obscured by the lumping of data across different palaeoecological and environmental conditions. Further studies of Cambrian trilobites with injuries represent a key direction for uncovering evidence for the Cambrian escalation event. Subjects Evolutionary Studies, Paleontology
In Cambrian fossil Lagerstätten like the Burgess Shale, exceptionally preserved arthropods constitute a large part of the taxonomic diversity, providing opportunities to study the early evolution of this phylum in detail. The anomalocaridids, large presumed pelagic predators, are particularly relevant owing to their unique combination of morphological characters and basal position in the arthropod stem lineage. Although isolated elements and fragmented specimens were first discovered over 100 years ago, subsequent findings of more complete bodies of Anomalocaris and Peytoia, especially in the 1980s, allowed for a better understanding of these enigmatic forms. Their evolutionary significance as stem group arthropods was further clarified by the recent discovery of a third anomalocaridid taxon, Hurdia. Here, examination of hundreds of Hurdia specimens from different stratigraphical layers within the Burgess Shale and Stephen Formation, combined with statistical analyses, provides a detailed description of the taphonomy, morphology and diversity of the genus and further elucidates anomalocaridid systematics. Hurdia is distinguished from other anomalocaridids in having mouthparts with extra rows of teeth, a large frontal carapace complex and diminutive swimming flaps with prominent setal structures. The two original species, H. victoria Walcott, 1912 and H. triangulata Walcott, 1912, are confirmed based on morphometric outline analyses of the frontal carapace components combined with stratigraphical evidence; a third species, Hurdia dentata Simonetta & Delle Cave, 1975, is synonymized with H. victoria. Morphology, preservation and stratigraphical distribution suggest that H. victoria and H. triangulata share the same type of frontal appendage; a second type of appendage, previously assigned to Hurdia (Morph A), belongs to Peytoia nathorsti. These and other morphological differences between the anomalocaridids may reflect different feeding strategies. Appendages and mouthparts of Hurdia indet. sp. are also identified from the Spence Shale Member of Utah, making Hurdia and Anomalocaris the most common and globally distributed anomalocaridid taxa.
The Middle Cambrian Spence Shale Member (Langston Formation) and Wheeler and Marjum Formations of Utah are known to contain a diverse soft-bodied fauna, but important new paleontological material continues to be uncovered from these strata. New specimens of anomalocaridids include the largest and smallest near complete examples yet reported from Utah. New material of stem group arthropods includes two new genera and species of arachnomorphs: Nettapezoura basilika and Dicranocaris guntherorum. Other new arachnomorph material includes a new species of Leanchoilia comparable to L. protogonia Simonetta, 1970; Leanchoilia superlata? Walcott, 1912; Sidneyia Walcott, 1911 a; and Mollisonia symmetrica Walcott, 1912. L. protogonia from the Burgess Shale is confirmed as a separate species and is not a composite fossil. The first example of the trilobite Elrathia kingii preserving traces of the appendages is described. In addition, new material of the bivalved arthropods Canadaspis Novozhilov in Orlov, 1960; Branchiocaris Briggs, 1076; Waptia Walcott, 1912; and Isoxys Walcott, 1890 is described.
We redescribe the morphology of Yohoia tenuis (Chelicerata sensu lato) from the Cambrian Burgess Shale Lagersta ̈tte. The morphology of the most anterior, promi- nent, so-called great appendage changes throughout ontog- eny. While its principal morphology remains unaltered, the length ratios of certain parts of the great appendage change significantly. Furthermore, it possesses a special jack-knifing mechanism, i.e. an elbow joint: the articulation between the distal one of the two peduncle elements and the most proxi- mal of the four spine-bearing claw elements. This morphol- ogy might have enabled the animal to hunt like a modern spearer-type mantis shrimp, an analogy enhanced by the sim- ilarly large and protruding eyes. For comparison, details of specimens of selected other great-appendage arthropods from the Lower Cambrian Chengjiang Lagersta ̈tte have been inves- tigated using fluorescence microscopy. This revealed that the morphology of the great appendage of Y. tenuis is much like that of the Chengjiang species Fortiforceps foliosa and Jianfen- gia multisegmentalis. The morphology of the great appendage of the latter is even more similar to the morphology devel- oped in early developmental stages of Y. tenuis, while the morphology of the great appendage of F. foliosa is more sim- ilar to that of later developmental stages of Y. tenuis. The arrangement of the elbow joint supports the view that the great appendage evolved into the chelicera of Chelicerata sensu stricto, as similar joints are found in various ingroup taxa such as Xiphosura, Opiliones or Palpigradi. With this, it also supports the interpretation of the great appendage to be homologous with the first appendage of other arthropods.
Five anomalocaridids are described from the Lower Cambrian Chengjiang fauna of China: Anomalocaris saron sp.n., Anomalocaris sp., Amplectobelua symbrachiata gen. et sp.n., Cucumericrus decoratus gen. et sp.n., and Parapeytoia yunnanensis gen. et sp.n. Ventral trunk appendages are reported for the first time. In C. decoratus and P. yunnanensis, each appendage has a distal segmented walking leg, and a wide lateral extension of a long proximal portion forms the structure previously described as a lateral fin. Furthermore, the structure of the dorsum is elucidated. The supposed ventrolateral gills are flat scales covering the back in transverse rows. The mouth was directed backwards, as in the Middle Cambrian Opabinia regalis, and not directed ventrally as in previous reconstructions. The radial arrangement of the circum-oral sclerites suggests that anomalocaridids were related to aschelminth worms rather than to arthropods.
Extant arthropods are diverse and ubiquitous, forming a major constituent of most modern ecosystems. Evidence from early Palaeozoic Konservat Lagerstätten indicates that this has been the case since the Cambrian. Despite this, the details of arthropod origins remain obscure, although most hypotheses regard the first arthropods as benthic predators or scavengers such as the fuxianhuiids or megacheirans ('great-appendage' arthropods). Here, we describe a new arthropod from the Tulip Beds locality of the Burgess Shale Formation (Cambrian, series 3, stage 5) that possesses a weakly sclerotized thorax with filamentous appendages, encased in a bivalved carapace, and a strongly sclerotized, elongate abdomen and telson. A cladistic analysis resolved this taxon as the basal-most member of a paraphyletic grade of nekto-benthic forms with bivalved carapaces. This grade occurs at the base of Arthropoda (panarthropods with arthropodized trunk limbs) and suggests that arthrodization (sclerotization and jointing of the exoskeleton) evolved to facilitate swimming. Predatory and fully benthic habits evolved later in the euarthropod stem-lineage and are plesiomorphically retained in pycnogonids (sea spiders) and euchelicerates (horseshoe crabs and arachnids).
Continuing debate over the evolution and morphology of the arthropod head has led to considerable interest in the relevance of the evidence from the fossil record. However, dispute over homology and even presence of appendages and sclerites in Cambrian arthropods has resulted in widely differing views of their significance. The head structures of several important taxa, Fuxianhuia, Canadaspis, Odaraia, Chengjiangocaris and Branchiocaris are redescribed, revealing the essential similarity between them. In particular, all possessed an anterior sclerite, probably followed by a large posterior, ventral sclerite that is likely to be homologous to the hypostome of trilobites. The presence of a similar feature in Sanctacaris is also possible, but less well-supported. An anterior sclerite, usually bearing eyes, as in Fuxianhuia, appears to be a widespread feature of basal arthropods. Whether or not this sclerite represents an original articulating protocerebral segment on its own is, however, open to debate.
A new Burgess Shale-type assemblage, from the Stephen Formation of the southern Canadian Rocky Mountains, is described herein. It occurs near Stanley Glacier in Kootenay National Park, 40 km southeast of the type area near Field, British Columbia. While at least a dozen Burgess Shale localities are known from the "thick" Stephen Formation, the Stanley Glacier locality represents the first discovery of Burgess Shale-type fossils from the "thin" Stephen Formation. The Cathedral Escarpment, an important regional paleotopographic feature, has been considered important to the paleoecologic setting and the preservation of the Burgess Shale biota. However, the Stanley Glacier assemblage was preserved in a distal ramp setting in a region where no evidence of an escarpment is present. The low-diversity assemblage contains eight new soft-bodied taxa, including the anomalocaridid Stanleycaris hirpex n. gen., n. sp. (new genus, new species). Nektonic or nektobenthic predators represent the most diverse group, whereas in relative abundance, the assemblage is dominated by typical Cambrian shelly benthic taxa. The low diversity of both the benthic taxa and the ichnofauna, which includes diminutive trace fossils associated with carapaces of soft-bodied arthropods, suggests a paleoenvironment with restrictive conditions. The Stanley Glacier assemblage expands the temporal and geographic range of the Burgess Shale biota in the southern Canadian Rockies, and suggests that Burgess Shale-type assemblages may be common in the "thin" Stephen Formation, which is regionally widespread.
Membership of Arthropoda in a clade of molting animals, the Ecdysozoa, has received a growing body of support over the past
10years from analyses of DNA sequences from many genes together with morphological characters involving the cuticle and its
molting. Recent analyses based on broad phylogenomic sampling strengthen the grouping of cycloneuralian worms and arthropods
as Ecdysozoa, identify the velvet worms (Phylum Onychophora) as the closest living relatives of arthropods, and interpret
segmentation as having separate evolutionary origins in arthropods and annelid worms. Determining whether the water bears
(Phylum Tardigrada) are more closely related to onychophorans and arthropods or to unsegmented cycloneuralians such as roundworms
(Nematoda) is an open question. Fossil taxa such as the Cambrian anomalocaridids provide a combination of arthropod and cycloneuralian
characters that is not observed in any living ecdysozoan. Fossils break up long branches and help to resolve the sequence
of character acquisition at several critical nodes in the arthropod tree, notably in a suite of Cambrian lobopodians that
may include the stem groups of each of the major panarthropod lineages.
The Cambro-Ordovician anomalocaridids are large ecdysozoans commonly regarded as ancestors of the arthropods and apex predators. Predation is indicated partly by the presence of an unusual "peytoia"-type oral cone, which is a tetraradial outer ring of 32 plates, four of which are enlarged and in perpendicular arrangement. This oral cone morphology was considered a highly consistent and defining characteristic of well-known Burgess Shale taxa. It is here shown that Anomalocaris has a different oral cone, with only three large plates and a variable number of smaller and medium plates. Its functional morphology suggests that suction, rather than biting, was used for food ingestion, and that anomalocaridids in general employed a range of different scavenging and predatory feeding strategies. Removing anomalocaridids from the position of highly specialized trilobite predators forces a reconsideration of the ecological structure of the earliest marine animal communities in the Cambrian.
Burgess Shale-type deposits provide invaluable insights into the early evolution of body plans and the ecological structure of Cambrian communities, but a number of species, continue to defy phylogenetic interpretations. Here we extend this list to include a new soft-bodied animal, Siphusauctum gregarium n. gen. and n. sp., from the Tulip Beds (Campsite Cliff Shale Member, Burgess Shale Formation) of Mount Stephen (Yoho National Park, British Columbia). With 1,133 specimens collected, S. gregarium is clearly the most abundant animal from this locality.
This stalked animal (reaching at least 20 cm in length), has a large ovoid calyx connected to a narrow bilayered stem and a small flattened or bulb-like holdfast. The calyx is enclosed by a flexible sheath with six small openings at the base, and a central terminal anus near the top encircled by indistinct openings. A prominent organ, represented by six radially symmetrical segments with comb-like elements, surrounds an internal body cavity with a large stomach, conical median gut and straight intestine. Siphusauctum gregarium was probably an active filter-feeder, with water passing through the calyx openings, capturing food particles with its comb-like elements. It often occurs in large assemblages on single bedding planes suggesting a gregarious lifestyle, with the animal living in high tier clusters. These were probably buried en masse more or less in-situ by rapid mud flow events.
Siphusauctum gregarium resembles Dinomischus, another Cambrian enigmatic stalked animal. Principal points of comparison include a long stem with a calyx containing a visceral mass and bract-like elements, and a similar lifestyle albeit occupying different tiering levels. The presence in both animals of a digestive tract with a potential stomach and anus suggest a grade of organization within bilaterians, but relationships with extant phyla are not straightforward. Thus, the broader affinities of S. gregarium remain largely unconstrained.
Until recently, intricate details of the optical design of non-biomineralized arthropod eyes remained elusive in Cambrian Burgess-Shale-type deposits, despite exceptional preservation of soft-part anatomy in such Konservat-Lagerstätten. The structure and development of ommatidia in arthropod compound eyes support a single origin some time before the latest common ancestor of crown-group arthropods, but the appearance of compound eyes in the arthropod stem group has been poorly constrained in the absence of adequate fossils. Here we report 2-3-cm paired eyes from the early Cambrian (approximately 515 million years old) Emu Bay Shale of South Australia, assigned to the Cambrian apex predator Anomalocaris. Their preserved visual surfaces are composed of at least 16,000 hexagonally packed ommatidial lenses (in a single eye), rivalling the most acute compound eyes in modern arthropods. The specimens show two distinct taphonomic modes, preserved as iron oxide (after pyrite) and calcium phosphate, demonstrating that disparate styles of early diagenetic mineralization can replicate the same type of extracellular tissue (that is, cuticle) within a single Burgess-Shale-type deposit. These fossils also provide compelling evidence for the arthropod affinities of anomalocaridids, push the origin of compound eyes deeper down the arthropod stem lineage, and indicate that the compound eye evolved before such features as a hardened exoskeleton. The inferred acuity of the anomalocaridid eye is consistent with other evidence that these animals were highly mobile visual predators in the water column. The existence of large, macrophagous nektonic predators possessing sharp vision--such as Anomalocaris--within the early Cambrian ecosystem probably helped to accelerate the escalatory 'arms race' that began over half a billion years ago.
24 p., 15 fig. http://paleo.ku.edu/contributions.html
The Burgess Shale has been an anomalous geologic unit ever since Walcott named it in 1911 as the geographic equivalent of the Ogygopsis Shale in the Middle Cambrian Stephen Formation of southeastern British Columbia, but it has never been recognized outside of its type locality, so its status relative to the Stephen Formation remained uncertain. The geologic setting of the Burgess Shale was determined by Aitken and Fritz in 1968, when they recognized the Cathedral Escarpment and divided the Stephen Formation into a "thin" platformal succession on top of the Escarpment, and a "thick" basinal succession, which included Walcott's Burgess Shale, in front. Fieldwork by Royal Ontario Museum parties between 1982 and 1997 has now demonstrated that the thin and thick Stephen successions lie within different facies belts and should be regarded as separate formations; the Stephen Shale Formation is part of the Middle Carbonate Belt succession, whereas the name Burgess Shale Formation is applied to the thick basinal succession within the Outer Detrital Belt Chancellor Group. Ten distinct members are recognized in the Burgess Shale: Kicking Horse Shale, Yoho River Limestone, Campsite Cliff Shale, Wash Limestone, Walcott Quarry Shale, Raymond Quarry Shale, Emerald Lake Oncolite, Odaray Shale, Paradox Limestone, and Marpole Limestone. In contrast to the Stephen Shale Formation with its nonsequences, the thicker Burgess Shale Formation seems to represent continuous deposition spanning the Glossopleura to Bathyuriscus-Elrathina zonal boundary, incorporating the Polypleuraspis insignis and Pagetia bootes subzones and the main part of the Pagetia walcotti subzone.
Most of the specimens of Myoscolex ateles Glaessner, 1979, the most abundant soft-bodied taxon in the Big Gully fauna from the Lower Cambrian Emu Bay Shale of South Australia, preserve only the phosphatized trunk muscles, in striking contrast to the organic residues that characterize other Burgess-Shale-type biotas. This is the oldest phosphatized muscle tissue and the first thus far reported from the Cambrian. The extent of phosphatization implies a source in addition to the animal itself, and this is reflected in high levels of phosphate in the Big Gully sequence compared to other shales. The apparent anomaly posed by the extensive preservation of labile muscle tissue as opposed to the more decay resistant cuticle is explained by the role of bacterial processes in the preservation of soft tissues. New specimens of Myoscolex reveal a variable number of trunk somites with possible tergites, and flap-like appendages. There is evidence for at least three eyes on the head, and a proboscis may have been present. An annelid affinity is rejected and Myoscolex is reinterpreted as an Opabinia-like animal with possible affinities with the arachnomorph arthropods.
Simple yet effective methods are available to enhance photographic images of low-contrast and low-relief specimens, such as fossils in shales, without manipulating or retouching the photographs. By applying polarizing filters to camera and light-source(s) in a way analogous to crossing nicols in a petrographic microscope, dramatic results can be achieved where there is a difference in reflectance between fossil and matrix, as with many coalified fossils. For example, this method is ideal for bringing out the shiny films representing soft tissues of Middle Cambrian Burgess Shale fossils. It is also useful in reducing reflections and increasing contrast in specimens that cannot be immersed in liquid (e.g., the Lower Cambrian Chengjiang fauna). Plants and graptolites in shales are other examples of suitable objects for this method. In addition, the use of digital imaging now makes it very easy to use interference between two versions to bring out differences. In this way, images of the same object taken with and without crossed nicols can be contrasted, as well as different colour channels. The result may be a dramatic improvement in the definition of hard-to-see or hard-to-image structures.
Over the last 35 years, more than 200 species have been described from the Lower Cambrian Chengjiang Lagerstatte. The body plans typical of that time may continue an evolutionary sequence with hidden Precambrian origins; many related forms are still represented in the Middle Cambrian, in the Burgess Shale. Their exquisite preservation allows the detailed analysis of features such as cuticular structures, and especially the morphology of the eyes. Many of the different eye systems known in recent animals are already present in the Chengjiang fauna. The existence of "simple eyes" like ocelli is discussed, the main emphasis however is laid on the visual systems themain of arthropods which dominate theChengjiang fauna. The arthropods that bore these eyes were all adapted to particular life habitats, while the design of visual systems is conditioned by the availability of light and the need for acute vision. All visual systems have to obey the same physical rules in the same way, and an analysis of the structure of fossilised eyes, in comparison to those of marine arthropods living today may reveal how, and under which conditions the now fossilised visual organs may have worked. The result of the investigations presented here is that some of the Lower Cambrian arthropods of the Chengjiang Fauna show "experimental" designs, some of which failed and are no longer present, while others developed or are still represented today. By the application of modern physiological methods these arthropods can be confidently assigned to a life habitat and to light dependent life-styles. A functional analysis of the eye systems of Chengjiang arthropods is presented, with a discussion of the relevance of these functions to ecology. ©2012 E. Schweizerbartsche Verlagsbuchhandlung, Stuttgart, Germany.
Organic-walled fossils are generally explicable as a coincidence of original, relatively recalcitrant, extra-cellular materials and more or less anti-biotic depositional circumstances. One of the most pervasive natural inhibitors of biodegradation results from substrate and enzyme adsorption onto, and within, clay minerals; such interactions are likely responsible for many of the organic-walled fossils preserved in clastic sediments. Close examination of the fossil Lagerstatte of the Burgess Shale (Middle Cambrian, British Columbia) reveals that most of its so-called soft-bodied fossils are composed of primary (although kerogenized) organic carbon. Their preservation can be attributed to pervasive clay-organic interactions as the organisms were transported in a moving sediment cloud and buried with all cavities and spaces permeated with fine grained clays. -from Author
The remarkable “evolution” of the reconstructions of Anomalocaris , the extraordinary predator from the 515 million year old Middle Cambrian Burgess Shale of British Columbia, reflects the dramatic changes in our interpretation of early animal life on Earth over the past 100 years. Beginning in 1892 with a claw identified as the abdomen and tail of a phyllocarid crustacean, parts of Anomalocaris have been described variously as a jellyfish, a sea-cucumber, a polychaete worm, a composite of a jellyfish and sponge, or have been attached to other arthropods as appendages. Charles D. Walcott collected complete specimens of Anomalocaris nathorsti between 1911 and 1917, and a Geological Survey of Canada party collected an almost complete specimen of Anomalocaris canadensis in 1966 or 1967, but neither species was adequately described until 1985. At that time they were interpreted by Whittington and Briggs to be representatives of “a hitherto unknown phylum.”
Here, using recently collected specimens, the two species are newly reconstructed and described in the genera Anomalocaris and Laggania , and interpreted to be members of an extinct arthropod class, Dinocarida, and order Radiodonta, new to science. The long history of inaccurate reconstruction and mistaken identification of Anomalocaris and Laggania exemplifies our great difficulty in visualizing and classifying, from fossil remains, the many Cambrian animals with no apparent living descendants.
The Cambrian Opabinia and Anomalocaris are odd animals known mainly from the Middle Cambrian Burgess Shale. Opabinia has usually been regarded as an arthropod, eg as a branchiopod crustacean. Parts of Anomalocaris have been referred to three or four different phyla. Recent redescriptions have clarified much of their morphology and resulted in their removal from the arthropods. Additional observations and considerations indicate that the two genera have important similarities, including scale-like structures arranged segmentally in transverse dorsal sets, which are separated by transverse tergal plates. Although external views are rare, traces of segmented appendages are identified in Anomalocaris. The animals are therefore again considered as arthropods, although they do not seem to be related to any of the other arthropod phyla.-Author
The ancestor of the arthropods is widely thought to have possessed a hydrostatic skeleton surrounded by peripheral longitudinal and circular musculature, as exhibited by the extant onychophorans. However, the transition to a lever-style musculature system with an articulating exoskeleton poses a difficult problem in functional evolution: did the musculature or the exoskeleton evolve first, and how? Here, by reference to the musculature of the Lower Cambrian stem-group arthropod Pambdelurion, the problem is resolved in terms of preadaptation and functional degeneracy without recourse to saltational notions. Cambrian taxa lying in the stem-groups of the modern phyla may thus be shown to provide unique evidence for the functional progression involved in the assembly of the extant body plans and obviate the need for exotic genetic or developmental mechanisms to explain the evolution of integrated and complex body plans. The notion of the phylum representing a particularly significant level of organization is thereby brought into question.
A new arthropod, Kootenichela deppi n. gen. n. sp., is described from the Stanley Glacier exposure of the middle Cambrian (Series 3, Stage 5) Stephen Formation in Kootenay National Park (British Columbia, Canada). This taxon possesses a number of primitive arthropod features such as an elongate, homonomous trunk (consisting of at least 29 segments), poorly sclerotised trunk appendages, and large pedunculate eyes associated with an anterior (ocular) sclerite. The cephalon encompasses a possible antenna-like appendage and enlarged raptorial appendages with a bipartite peduncle and three spinose distal podomeres, indicative of megacheiran (“great-appendage” arthropod) affinities. The relationships of megacheirans are controversial, with them generally considered as either stem-euarthropods or a paraphyletic stem-lineage of chelicerates. An extensive cladistic analysis resolved Kootenichela as sister-taxon to the enigmatic Worthenella cambria from the middle Cambrian (Series 3, Stage 5), Burgess Shale Formation in Yoho National Park (British Columbia), which is herein reinterpreted as a megacheiran arthropod. Based on their sister-group relationship, both taxa were placed in the new family Kootenichelidae, to which Pseudoiulia from the Chengjiang biota is also tentatively assigned. All of these taxa possess an elongate, multi-segmented body and subtriangular exopods. This family occupies a basal position within a paraphyletic Megacheira, the immediate outgroup of Euarthropoda (crown-group arthropods). The resultant topology indicates that analyses that have resolved megacheirans as stem-chelicerates have done so because they have rooted on inappropriate taxa, e.g., trilobitomorphs and marrellomorphs.
Two species of Anomalocaris co‐occur in the Emu Bay Shale (Cambrian Series 2, Stage 4) at Big Gully, Kangaroo Island. Frontal appendages of Anomalocaris briggsi Nedin, 1995, are more common than those of Anomalocaris cf. canadensis Whiteaves, 1892, at a quarry inland of the wave‐cut platform site from which these species were originally described. An oral cone has the three large, node‐bearing plates recently documented for Anomalocaris canadensis, confirming that Anomalocaris lacks a tetraradial ‘Peytoia’ oral cone and strengthening the case for the identity of the Australian specimens as Anomalocaris. Disarticulated anomalocaridid body flaps are more numerous in the Emu Bay Shale than in other localities, and they preserve anatomical details not recognized elsewhere. Transverse lines on the anterior part of the flaps, interpreted as strengthening rays or veins in previous descriptions of anomalocaridids, are associated with internal structures consisting of a series of well‐bounded, striated blocks or bars. Their structure is consistent with a structural function imparting strength to the body flaps. Setal structures consisting of a series of lanceolate blades are similar to those of other anomalocaridids and are found in isolation or associated with body flaps. A single specimen also preserves putative gut diverticula. The morphology of the appendages, oral cone, gut diverticula and compound eyes of Anomalocaris, along with its large size, suggests that it was an active predator, and specimens of coprolites containing trilobite fragments and trilobites with prominent injuries have been cited as evidence of anomalocaridid predation on trilobites. Based on frontal appendage morphology, Anomalocaris briggsi is inferred to have been a predator of soft‐bodied animals exclusively and only Anomalocaris cf. canadensis may have been capable of durophagous predation on trilobites, although predation (including possible cannibalism) by Redlichia could also explain the coprolites and damage to trilobite exoskeletons found in the Emu Bay Shale.
Three categories of fossil aggregates are recognized in the Lower Cambrian Maotianshan Shale biota from SW China: (1) elliptical aggregates with randomly distributed exoskeletal remains of typically small- to medium-size bivalved arthropods (e.g, ostracode-like bradoriids, phyllocarid-like waptiids), hyoliths, and trilobites are interpreted as coprolites, possibly produced by anomalocaridids (e.g., waptiid-rich coprolites) and/or unknown epibenthic predators; (2) elongate, ribbon-like aggregates composed of oriented small hyolith shells, interpreted as the feces of infaunal carnivorous worms such as priapulids; and (3) concentric aggregates, typically with a central nucleus (e.g, remains of medusoid eldoniids or bivalved arthropod carapaces) and peripheral exoskeletal fragments, possibly generated by bottom currents whirling around carcasses. These new coprolite data add to morphofunctional information obtained from fossil organisms and indicate that predation occurred at different levels of the water column with: (1) endobenthic predators (diverse priapulid fauna) feeding near the sediment-water interface; (2) epibenthic predators / scavengers (almost exclusively arthropods); (3) predators living in the lower levels of the water column (e.g., anomalocaridids); and (4) mid-water predators exploiting upper levels in the water column (e.g, eldoniids, ctenophores, chaetognaths). Communities living at or close to the water-sediment interface (epibenthic sensu stricto, meiobenthic, and demersal animals) were exposed to a multidirectional predatorial pressure from infaunal, epifaunal, and mid-water predators. Although predation was diverse, nothing indicates that the food chain extended beyond the level of primary carnivores. Animals already had acquired complex behaviors such as hunting (e.g., anomalocaridids, priapulids) and predator avoidance in which sensory systems were involved. The example of the Maotianshan Shale indicates that the burst of anatomical innovations (new body plans) that characterizes the early Cambrian also was accompanied by the rapid development of new feeding strategies and by an unprecedented expansion of ecological interactions (prey-predator relationships).
The Burgess Shale arthropod Leanchoilia superlata Walcott 1912, commonly preserves a three-dimensional axial structure generally interpreted as gut contents. Thin-section examination shows this instead to be phosphatized biserially repeated midgut glands, including exceptional preservation of subcellular features. The preferential mineralization of these structures is related to their unusually high chemical reactivity and probably to an internal source of phosphate. Sub-millimetric lineations previously interpreted as annular musculature are in fact planar, sometimes radially arranged, subdivisions of these glands. Ventral rows of isolated phosphate patches appear to represent the same tissue.
In extant arthropods, extensively developed midgut glands are related to a rich but infrequent diet with a primary function in storage. Their conspicuous occurrence in unambiguous fossil predators such as Sidneyia and Laggania ( Anomalocaris ) suggests they served a similar role in the Cambrian; by extension, their conspicuous occurrence in Leanchoilia suggests it was a predator or scavenger.
Phosphatized midguts with a structure essentially indistinguishable from that of Leanchoilia are also found in Burgess Shale Odaraia, Canadaspis, Perspicaris, Sidneyia, Anomalocaris , and Opabinia. All are characterized by a distinctive sub-millimetric arrangement of planar elements that is not found in extant arthropods or trilobites, suggesting they diverged before the last common ancestor of extant forms; i.e., they represent stem-group arthropods.
Three-dimensionally preserved guts are widely preserved in the Lower Cambrian Chengjiang biota but, unlike those in the Burgess Shale, appear to be filled with sediment. Although generally interpreted as evidence of deposit feeding, the form of these structures points to early permineralization of (sediment-free) midgut glands that were subsequently altered to clay minerals. There is no evidence of deposit feeding in the Chengjiang; indeed, there is a case to be made for deposit feeding not being generally exploited generally until after the Cambrian.
Fossils with three-dimensionally preserved axes from the Lower Cambrian Sirius Passet biota have been interpreted as lobopodians; however, most of the putative lobopodian features find alternative interpretations as aspects of Leanchoilia -type midgut glands. Although Kerygmachela is reliably identified as a stem-group arthropod, its phylogenetic position remains unresolved owing to the non-preservation of critical external features and to the plesiomorphic nature of its Leanchoilia -type midgut.
Isolated specimens of the appendage Anomalocaris canadensis have long
been known; a single incomplete specimen of an animal having a pair of
these appendages attached anteriorly is described. Seven dorsoventrally
compressed, partly complete individuals of a similar animal that had a
different pair of appendages (`F' of Briggs 1979) attached anteriorly
are described, together with two obliquely compressed individuals that
are thought to be conspecific. Surrounding the mouth of this latter
species is a circlet of plates identical with the supposed medusoid
coelenterate Peytoia nathorsti; this species is referred to
Anomalocaris; Laggania is a junior synonym. As now understood,
Anomalocaris was an animal that reached a length of 0.5 m, the elongate
body having a head region bearing one pair of large, lateral eye lobes,
each borne on a short stalk, the single pair of appendages attached at
the ventral, anterior margin. The 13 segments of the appendage in A.
canadensis bore paired spines on the inner side, short spines on the
outer side, and there was a terminal, spinose 14th segment. The
appendage in A. nathorsti consisted of 11 segments, the 2nd to 10th
bearing on the inner side a graduated series of spinose blades, and
spines on the lateral and outer sides, the terminal 11th segment ending
in a group of spines. The circlet of plates surrounding the mouth was
situated ventrally on the head region immediately behind the appendages;
the plates bore teeth and the circlet constituted a jaw mechanism;
additional groups of spines were present in the buccal cavity. Beneath
the head region, behind the mouth, were three pairs of semicircular
flaps, strongly overlapping: on the tapering trunk were 11 pairs of
triangular lateral lobes, widest at the mid-length of the trunk, reduced
progressively in size backward. These lobes were strongly overlapping in
the same sense as the flaps on the head, and attached low on the sides.
The trunk termination was short and blunt, without any projecting spine
or lobe. Attached to the side of the body, above each flap and lateral
lobe, was a multi-lamellar structure, apparently a gill. A thin cuticle
covered the head region dorsally, and ventrally around the appendages
and jaw circlet, behind this becoming a lateral strip that narrowed
backward. It is suggested that a thin cuticle covered the trunk region
dorsally and hung down beside the gills; this covering may have been
continuous, but possibly was divided into tergites. Irregular patches of
apatite, and some matrix, occur in the trace of the alimentary canal,
which extended to the tip of the trunk. Mineralized patches occur in
association with the gills, and as transverse strips, presumed traces of
some internal organ or structure. The cuticle of the appendages and jaw
circlet was presumably stout, hence these parts of the body were more
resistant to decay and so were preserved in isolation. The thin cuticle
of the lateral lobes shows rays which were presumably thicker and
strengthening in function. We suggest that this animal, the largest
known from Cambrian rocks, swam by using the series of closely spaced
lateral lobes essentially as a lateral fin along which waves of motion
were propagated. If the waves were moved in either the same, or
opposite, sense on each side, considerable manoeuvrability would have
resulted. The anterior pair of appendages, and jaw mechanism, would have
made Anomalocaris a formidable predator, particularly on soft-bodied
benthos including the abundant arthropods without a mineralized
exoskeleton. No fragments of hard parts have been observed in the gut,
but there is evidence that it may have inflicted wounds on trilobites.
Anomalocaris was a metameric animal, and had one pair of jointed
appendages and a unique circlet of jaw plates. We do not consider it an
arthropod, but the representative of a hitherto unknown phylum. It is
best known from A. nathorsti, the single specimen of A. canadensis
having a different appendage but the rest of the body similar, probably
including the jaw circlet. The evidence is insufficient to reach any
conclusion on whether or not these two `species' may be sexual dimorphs
of a single species. The single specimen of Amiella ornata is
redescribed. It shows what may be lateral lobes like those of
Anomalocaris, but other features unlike it. We conclude that this
specimen is not an example of Sidneyia inexpectans, and is too
incomplete for its relationship to be determined.
It has often been taken for granted that the outer branch of trilobite limbs had a gill function. Since there are no thorough analyses of the case, we decided to make an attempt. Morphological characteristics of arthropod gills are defined. There is a need for a large area/volume ratio with a cuticle thin enough to perform gaseous exchange and an anastomosing hemocoel for blood circulation. Protection and stability are often provided in carapace folds, where the upper/dorsal sheet is sclerotized and the lower one houses the gill area. Where the bivalved ostracode carapace is not attached to the body, it is such a fold. More often segmental folds are in the shape of lateral tergopleurae without ventral gill areas. Vascular channels and pillars connecting the sclerotized and non-sclerotized cuticle of the two sides are typical features, and are traced in trilobites. The trace is seen only as a pattern in the pleural exoskeleton between the axis and the doublure, exactly the area where there was no ventral exoskeleton. This therefore seems to be the place for the gills. The gill lamellae in limulids are folds from the basal part of the appendage, whereas the lamellae in trilobites are setae on a distal limb branch, the exopod; the two types of lamellar structures thus are not homologous. It was concluded in a previous study of ours that the exopod setae of trilobites had mechanical rather than respiratory functions. The conservation of the trilobite type of exopod throughout the lamellipedians indicates a fundamental role as ventilator of the gills.
Marine ecosystems with complex trophic structure and dominated by animals started to build up in the Early Cambrian. Fossil evidence from exceptional fossil localities such as the Chengjiang Lagerstätte from South China indicate a high level of biological interactivity (e.g. prey–predator relationships) and the colonization of a wide range of pelagic and benthic niches by predators, scavengers, and detritus and suspension feeders. Swimmers are numerous, but there is no evidence for the extensive occupation of the water column by the Early Cambrian. On the contrary, animal life may have concentrated in hyperbenthic environments, close to the sea bottom. This would have been the initial step towards the colonization of the whole pelagic realm and the building-up of pelagic food chains. A chain of biotic innovations and events seems to have catalyzed both the animal diversification and the build-up of a completely new type of ecosytem, with: (1) the achievement of complex nervous systems, visual organs and motor functions; (2) the introduction of new selective pressure (e.g. predation and feed-back effects); and (3) the colonization of new niches. The role of environmental factors (e.g. oxygen, water chemistry, climate) may have been important in the early stages of metazoan evolution, but was probably negligible in the ecological turnover itself that takes place in the Early Cambrian. Close resemblances between the trophic structure of present-day ecosystems and that of Cambrian ones are confirmed by fossil data and recent mathematical models. This unprecedented increase of interdependence between animal species and trophic levels probably increased the general stability of marine ecosystems, but made them for the first time in their history, highly vulnerable to environmental perturbations. This will largely influence the post-Cambrian evolution of the marine world.
The Burgess Shale has been an anomalous geologic unit ever since Walcott named it in 1911 as the geographic equivalent of the Ogygopsis Shale in the Middle Cambrian Stephen Formation of southeastern British Columbia, but it has never been recognized outside of its type locality, so its status relative to the Stephen Formation remained uncertain. The geologic setting of the Burgess Shale was determined by Aitken and Fritz in 1968, when they recognized the Cathedral Escarpment and divided the Stephen Formation into a "thin" platformal succession on top of the Escarpment, and a "thick" basinal succession, which included Walcott's Burgess Shale, in front. Fieldwork by Royal Ontario Museum parties between 1982 and 1997 has now demonstrated that the thin and thick Stephen successions lie within different facies belts and should be regarded as separate formations; the Stephen Shale Formation is part of the Middle Carbonate Belt succession, whereas the name Burgess Shale Formation is applied to the thick basinal succession within the Outer Detrital Belt Chancellor Group. Ten distinct members are recognized in the Burgess Shale: Kicking Horse Shale, Yoho River Limestone, Campsite Cliff Shale, Wash Limestone, Walcott Quarry Shale, Raymond Quarry Shale, Emerald Lake Oncolite, Odaray Shale, Paradox Limestone, and Marpole Limestone. In contrast to the Stephen Shale Formation with its nonsequences, the thicker Burgess Shale Formation seems to represent continuous deposition spanning the Glossopleura to Bathyuriscus-Elrathina zonal boundary, incorporating the Polypleuraspis insignis and Pagetia bootes subzones and the main part of the Pagetia walcotti subzone.
The Cambrian Opabinia Anomalocaris are odd animals known mainly from the Middle Cambrian Burgess Shale. Opabinia has usually been regarded as an arthropod, e.g. as a branchiopod crustacean. Parts of Anomalocaris have been referred to three or four different phyla. Recent redescriptions have clarified much of their morphology resulted in their removal from the arthropods. Additional observations considerations indicate that the two genera have important similarities, including scale-like structures arranged segmentally in transverse dorsal sets, which are separated by transverse tergal plates. Although external views are rare, traces of segmented appendages are identified in Anomalocaris. The animals are therefore again considered as arthropods, although they do not seem to be related to any of the other arthropod phyla.
The complex history of description of the anomalocaridids has partly been caused by the fragmentary nature of these fossils. Frontal appendages and mouth parts are more readily preserved than whole-body assemblages, so the earliest work on these animals examined these structures in isolation. After several decades of research, these disarticulated elements were assembled together to reconstruct the anomalocaridid body plan, and a total of three Burgess Shale genera, Anomalocaris, Laggania and Hurdia, were described in full. Here we present new frontal appendage material of additional anomalocaridid taxa from the ‘Middle’ Cambrian (Series 3) Burgess Shale Formation in Canada, showing that the diversity of anomalocaridids in this locality is even higher than previously thought. Material includes Amplectobelua stephenensis sp. nov., the first known occurrence of this genus outside of China; Caryosyntrips serratus gen. et sp. nov., which is similar to the Anomalocaris appendage but has a straighter outline and a different arrangement of spines; and an appendage that may be either the Laggania appendage or a third morph of the Hurdia appendage. The new anomalocaridid material is contemporaneous with the previously described taxa Anomalocaris, Laggania, and Hurdia, and the differences in morphology between the frontal appendages may reflect different feeding strategies. The stratigraphically lowest locality, S7 on Mount Stephen, yields material from all anomalocaridid taxa, but the assemblages in the younger quarries on Fossil Ridge are dominated by Anomalocaris and Hurdia only.
The ancestor of the arthropods is widely thought to have possessed a hydrostatic skeleton surrounded by peripheral longitudinal and circular musculature, as exhibited by the extant onychophorans. However, the transition to a lever-style musculature system with an articulating exoskeleton poses a difficult problem in functional evolution: did the musculature or the exoskeleton evolve first, and how? Here, by reference to the musculature of the Lower Cambrian stem-group arthropod Pambdelurion, the problem is resolved in terms of preadaptation and functional degeneracy without recourse to saltational notions. Cambrian taxa lying in the stem-groups of the modern phyla may thus be shown to provide unique evidence for the functional progression involved in the assembly of the extant body plans and obviate the need for exotic genetic or developmental mechanisms to explain the evolution of integrated and complex body plans. The notion of the phylum representing a particularly significant level of organization is thereby brought into question.
Kiisortoqia soperi gen. et sp. nov. is an arthropod species from the Early Cambrian Sirius Passet Lagerstätte of North Greenland. A head, incorporating four appendiferous segments and biramous limbs, with an anteroposteriorly compressed basipod with a spine bearing median edge, support the euarthropod affinities of K. soperi gen. et sp. nov. Similarities with ‘short great appendage’ arthropods, or megacheirans, like the nine-segmented endopod, and the flap- or paddle-like exopod, may be symplesiomorphies. The antennula, however, resembles in composition and size the anteroventral raptorial appendage of anomalocaridids. Thus, the morphology of K. soperi gen. et sp. nov. provides additional support for the homologization of the anomalocaridid ‘great appendage’ with the appendage of the antennular or deutocerebral segment of extant Euarthropoda.© 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158, 477–500.
Anomalocaridids, giant lightly sclerotized invertebrate predators, occur in a number of exceptionally preserved early and middle Cambrian (542-501 million years ago) biotas and have come to symbolize the unfamiliar morphologies displayed by stem organisms in faunas of the Burgess Shale type. They are characterized by a pair of anterior, segmented appendages, a circlet of plates around the mouth, and an elongate segmented trunk lacking true tergites with a pair of flexible lateral lobes per segment. Disarticulated body parts, such as the anterior appendages and oral circlet, had been assigned to a range of taxonomic groups--but the discovery of complete specimens from the middle Cambrian Burgess Shale showed that these disparate elements all belong to a single kind of animal. Phylogenetic analyses support a position of anomalocaridids in the arthropod stem, as a sister group to the euarthropods. The anomalocaridids were the largest animals in Cambrian communities. The youngest unequivocal examples occur in the middle Cambrian Marjum Formation of Utah but an arthropod retaining some anomalocaridid characteristics is present in the Devonian of Germany. Here we report the post-Cambrian occurrence of anomalocaridids, from the Early Ordovician (488-472 million years ago) Fezouata Biota in southeastern Morocco, including specimens larger than any in Cambrian biotas. These giant animals were an important element of some marine communities for about 30 million years longer than previously realized. The Moroccan specimens confirm the presence of a dorsal array of flexible blades attached to a transverse rachis on the trunk segments; these blades probably functioned as gills.