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Articulated Halkieriids from the Lower Cambrian of North Greenland and their Role in Early Protostome Evolution
Philosophical Transactions B
Abstract
Articulated halkieriids of Halkieria evangelista sp. nov. are described from the Sirius Passet fauna in the Lower Cambrian Buen Formation of Peary Land, North Greenland. Three zones of sclerites are recognizable: obliquely inclined rows of dorsal palmates, quincuncially inserted lateral cultrates and imbricated bundles of ventro-lateral siculates. In addition there is a prominent shell at both ends, each with radial ornamentation. Both sclerites and shells were probably calcareous, but increase in body size led to insertion of additional sclerites but marginal accretion of the shells. The ventral sole was soft and, in life, presumably muscular. Recognizable features of internal anatomy include a gut trace and possible musculature, inferred from imprints on the interior of the anterior shell. Halkieriids are closely related to the Middle Cambrian Wiwaxia, best known from the Burgess Shale: this clade appears to have played an important role in early protostome evolution. From an animal fairly closely related to Wiwaxia arose the polychaete annelids; the bundles of siculate sclerites prefigure the neurochaetae whereas the dorsal notochaetae derive from the palmates. Wiwaxia appears to have a relic shell and a similar structure in the sternaspid polychaetes may be an evolutionary remnant. The primitive state in extant polychaetes is best expressed in groups such as chrysopetalids, aphroditaceans and amphinomids. The homology between polychaete chaetae and the mantle setae of brachiopods is one line of evidence to suggest that the latter phylum arose from a juvenile halkieriid in which the posterior shell was first in juxtaposition to the anterior and rotated beneath it to provide the bivalved condition of an ancestral brachiopod. H. evangelista sp. nov. has shells which resemble those of a brachiopod; in particular the posterior one. From predecessors of the halkieriids known as siphogonuchitids it is possible that both chitons (polyplacophorans) and conchiferan molluscs arose. The hypothesis of halkieriids and their relatives having a key role in annelid-brachiopod-mollusc evolution is in accord with some earlier proposals and recent evidence from molecular biology. It casts doubt, however, on a number of favoured concepts including the primitive annelid being oligochaetoid and a burrower, the brachiopods being deuterostomes and the coelom being an archaic feature of metazoans. Rather, the annelid coelom arose as a functional consequence of the transition from a creeping halkieriid to a polychaete with stepping parapodial locomotion.
... Strong doubts as to their polyplacophoran affi nities have been expessed (Qian and Bengtson 1989;Runnegar 1996;Qian et al. 1999). These "microchitons" (e.g., Stoliconus, Yangtzechiton, Luyanhaochiton, Meishucunchiton, Runnegarochiton, Tchangsichiton) most likely represent different types of dorsal sclerites of problematic animals, similar to pairs of dorsal plates of the remarkable taxon Halkieria evangelista discovered from the Sirius Passet Lagerstätte of the Atdabanian of Greenland (Conway Morris and Peel 1990) and interpreted as a stem-group brachiopod (Conway Morris and Peel 1995). However, the latest comparative study of Halkieria and Recent chitons (Vinther and Nielsen 2005) favored a molluscan affi nity of this enigmatic Cambrian fossil. ...
... Strong doubts as to their polyplacophoran affi nities have been expessed (Qian and Bengtson 1989;Runnegar 1996;Qian et al. 1999). These "microchitons" (e.g., Stoliconus, Yangtzechiton, Luyanhaochiton, Meishucunchiton, Runnegarochiton, Tchangsichiton) most likely represent different types of dorsal sclerites of problematic animals, similar to pairs of dorsal plates of the remarkable taxon Halkieria evangelista discovered from the Sirius Passet Lagerstätte of the Atdabanian of Greenland (Conway Morris and Peel 1990) and interpreted as a stem-group brachiopod (Conway Morris and Peel 1995). However, the latest comparative study of Halkieria and Recent chitons (Vinther and Nielsen 2005) favored a molluscan affi nity of this enigmatic Cambrian fossil. ...
... Late Cambrian Matthevia was also interpreted as a stromatolitic dweller (Runnegar et al. 1979). Articulated scleritomes of Halkieria evangelista were found in silts, which are assumed to accumulate in rather deep water and anoxic conditions (Conway Morris and Peel 1995). However, Halkieria fi nds may not be autochthonous and animals may have been transported from shallower environments. ...
... Strong doubts as to their polyplacophoran affi nities have been expessed (Qian and Bengtson 1989;Runnegar 1996;Qian et al. 1999). These "microchitons" (e.g., Stoliconus, Yangtzechiton, Luyanhaochiton, Meishucunchiton, Runnegarochiton, Tchangsichiton) most likely represent different types of dorsal sclerites of problematic animals, similar to pairs of dorsal plates of the remarkable taxon Halkieria evangelista discovered from the Sirius Passet Lagerstätte of the Atdabanian of Greenland (Conway Morris and Peel 1990) and interpreted as a stem-group brachiopod (Conway Morris and Peel 1995). However, the latest comparative study of Halkieria and Recent chitons (Vinther and Nielsen 2005) favored a molluscan affi nity of this enigmatic Cambrian fossil. ...
... Strong doubts as to their polyplacophoran affi nities have been expessed (Qian and Bengtson 1989;Runnegar 1996;Qian et al. 1999). These "microchitons" (e.g., Stoliconus, Yangtzechiton, Luyanhaochiton, Meishucunchiton, Runnegarochiton, Tchangsichiton) most likely represent different types of dorsal sclerites of problematic animals, similar to pairs of dorsal plates of the remarkable taxon Halkieria evangelista discovered from the Sirius Passet Lagerstätte of the Atdabanian of Greenland (Conway Morris and Peel 1990) and interpreted as a stem-group brachiopod (Conway Morris and Peel 1995). However, the latest comparative study of Halkieria and Recent chitons (Vinther and Nielsen 2005) favored a molluscan affi nity of this enigmatic Cambrian fossil. ...
... Late Cambrian Matthevia was also interpreted as a stromatolitic dweller (Runnegar et al. 1979). Articulated scleritomes of Halkieria evangelista were found in silts, which are assumed to accumulate in rather deep water and anoxic conditions (Conway Morris and Peel 1995). However, Halkieria fi nds may not be autochthonous and animals may have been transported from shallower environments. ...
This book brings together thirty-six experts on the evolution of the Mollusca to provide an up-to-date review of its evolutionary history. The Mollusca are the second largest animal phylum and boast a fossil record of over 540 million years. They exhibit remarkable anatomical diversity and include the bivalves (scallops, oysters, and clams), gastropods (limpets, snails, and slugs), and cephalopods (squid, cuttlefish, and octopus). This study treats each major taxon and supplies general information as well as overviews of evolution and phylogeny using data from different sources—morphological, ultrastructural, molecular, developmental, and from the fossil record.
... Shell-bearing organisms present in the Spence Shale include several brachiopod genera, hyoliths, as well as the mollusks Latouchella arguta Resser, 1939 and Skeemella radians Robison, 1988 (Kimmig et al., 2019). Halkieriids, Cambrian vermiform fossils covered by sclerites and bearing at least one shell (Conway Morris and Peel, 1995;Conway Morris and Caron, 2007;Zhao et al., 2017), have not been described from the Spence Shale, nor any of the other Utah Lagerst€ atten, but are known from the slightly younger Burgess Shale (Conway Morris and Caron, 2007). ...
... There are few Cambrian organisms known that bear a shell and have a slug-like body. The closest animals that have both these features are halkieriids, Cambrian vermiform fossils covered by sclerites and bearing at least one shell (Conway Morris and Peel, 1995;Conway Morris and Caron, 2007;Zhao et al., 2017). Complete specimens are known from several Cambrian deposits, including the Sirius Passet Lagerst€ atte (Conway Peel, 1990, 1995), the Burgess Shale (Conway Morris and Caron, 2007), and the Chengjiang Lagerst€ atten (Zhao et al., 2017). ...
... While Armilimax pauljamisoni shares the presence of a shell and the elongated body with these animals, there is no indication that A. pauljamisoni had a scleritome consisting of three distinct sclerite types, which all other described halkieriids share. In addition, A. pauljamisoni has a coiled/U-shaped gut, while Halkieria Poulsen, 1967 and Orthrozanclus Conway Morris and Caron, 2007 both have straight digestive tracts (Conway Morris and Peel, 1995;Conway Morris and Caron, 2007;Zhao et al., 2017). ...
A new shell-bearing organism with preserved soft tissue, Armilimax pauljamisoni n. gen. n. sp., is reported from the middle Cambrian (Miaolingian: Wuliuan) Miners Hollow locality of the Spence Shale of northern Utah. The described organism is known from a single articulated specimen and preserves a prominent shell, a slug-like body, as well as a U-shaped digestive tract. Its overall appearance is similar to halkieriids, but it does not preserve sclerites. The possible affinities of the new taxon and potential reasons for the presence of a U-shaped gut are discussed. Armilimax pauljamisoni is the first shell-bearing animal of its kind from the Great Basin and extends the diversity of body plans in the Spence Shale Fossil-Lagerstätte.
... Along with other exceptionally preserved Palaeozoic taxa, Canadia has featured heavily in discussions of the early evolution of Trochozoa (10,16,23,24), and the annelids of the Burgess Shale have long been recognized as an important source of evidence regarding the morphology of the annelid ancestor (9,16,25). Our new reconstruction of Canadia (Fig. 4A, fig. ...
... The gills of Canadia ( Fig. 1C and fig. S3) are distinct from those of extant annelids (11,17) and could be autapomorphic, although they share intriguing similarities in both morphology and attachment with molluscan ctenidia (11,23), which are also repeated on along the A-P axis in stem molluscs [e.g., Odontogriphus (39)]. It is likely that multiple repeated gills were present in the ancestral mollusc (24), and consequently, the branchiae could represent a deep homolog shared with molluscs (11,23). ...
... S3) are distinct from those of extant annelids (11,17) and could be autapomorphic, although they share intriguing similarities in both morphology and attachment with molluscan ctenidia (11,23), which are also repeated on along the A-P axis in stem molluscs [e.g., Odontogriphus (39)]. It is likely that multiple repeated gills were present in the ancestral mollusc (24), and consequently, the branchiae could represent a deep homolog shared with molluscs (11,23). Branchiae are phylogenetically widespread among annelids in both sedentary and errant taxa, and it is likely that they have multiple independent origins. ...
Annelid worms are a disparate, primitively segmented clade of bilaterians that first appear during the early Cambrian Period. Reconstructing their early evolution is complicated by the extreme morphological diversity in early diverging lineages, rapid diversification, and sparse fossil record. Canadia spinosa , a Burgess Shale fossil polychaete, is redescribed as having palps with feeding grooves, a dorsal median antenna and biramous parapodia associated with the head and flanking a ventral mouth. Carbonaceously preserved features are identified as a terminal brain, circumoral connectives, a midventral ganglionated nerve cord and prominent parapodial nerves. Phylogenetic analysis recovers neuroanatomically simple extant taxa as the sister group of other annelids, but the phylogenetic position of Canadia suggests that the annelid ancestor was reasonably complex neuroanatomically and that reduction of the nervous system occurred several times independently in the subsequent 500 million years of annelid evolution.
... These fossil taxa are clearly polychaetes, possessing well-developed parapodia, homonomous segmentation, and chaetae. Other taxa whose affinities are more obscure have also been linked with annelids, such as Wiwaxia corrugata from the Burgess Shale (Conway Morris 1985), and there has been an intense debate about how early trochozoans are related to each other and to extant phyla ( Fig. 3.2 E, F) (Conway Morris and Peel 1995, Eibye-Jacobsen 2004, Vinther et al. 2017, Zhao et al. 2017. The origin of annelids and the characters that define Annelida as a phylum have been featured heavily in these discussions (Eibye-Jacobsen 2004). ...
... primarily focused on the origin of chaetae and biomineralized sclerites, shells and valves, radulae, and segmentation (Conway Morris and Peel 1995, Eibye-Jacobsen 2004, Butterfield 2006, Vinther et al. 2017. Of these three taxa, only C. spinosa is unambiguously a polychaete, possessing differentiated and well-developed noto-and neurochaetae, prominent parapodial lobes, and a pair of palps ( Fig. 3.2 C) (Conway Morris 1979, Eibye-Jacobsen 2004. ...
... Although Wiwaxia is present in several Burgess Shale-type localities, its true geographic and stratigraphic range is revealed by the SCF record (Slater et al. 2017). Wiwaxia has been interpreted as a polychaete previously and was placed explicitly in the Phyllodocida (along with Canadia) by Butterfield (1990) or in the annelid stem group by Conway Morris and Peel (1995). Placing Wiwaxia in the crown or stem group of annelids has nontrivial implications for the hypotheses of character evolution leading to and within annelids. ...
... If sclerites are present on the ventral surface they are too small to be discerned (< 40 μ m). The ventral mantle is preserved as a smooth brown-stained surface ( Fig. 2a and Extended Data Figs 2a-d, 5,7). The mantle cavity (evident as a ridge in YPM 227515 and a colour difference in YPM 237255) extends along the entire length of the trunk. ...
... The position of the radula confirms that the shell plate is anterior. A posterior shell plate, such as that in Halkieria evangelista 3,5 (and probably also Oikozetetes), is absent (Figs 1, 2 and Extended Data Figs 1, 2): the cover of dorsal sclerites is uninterrupted where such a plate would be situated (Fig. 1). ...
... The phylogenetic position of sachitids and wiwaxiids, which have been grouped together into Halwaxiida by some authors 4 , has been a topic of debate. Sachitids have been interpreted as stem brachiopods 5,10 or basal aculiferan molluscs 6,11 , whereas halwaxiids as a whole have been considered to represent either stem molluscs 4,12 , or the stem group of both brachiopods and annelids 4 (see Supplementary Information). C. kroegeri provides new data, which allow the affinities of sachitids and wiwaxiids to be clarified. ...
Exceptionally preserved fossils provide crucial insights into extinct body plans and organismal evolution. Molluscs, one of the most disparate animal phyla, radiated rapidly during the early Cambrian period (approximately 535-520 million years ago (Ma)). The problematic fossil taxa Halkieria and Orthrozanclus (grouped in Sachitida) have been assigned variously to stem-group annelids, brachiopods, stem-group molluscs or stem-group aculiferans (Polyplacophora and Aplacophora), but their affinities have remained controversial owing to a lack of preserved diagnostic characters. Here we describe a new early sachitid, Calvapilosa kroegeri gen. et sp. nov. from the Fezouata biota of Morocco (Early Ordovician epoch, around 478 Ma). The new taxon is characterized by the presence of a single large anterior shell plate and polystichous radula bearing a median tooth and several lateral and uncinal teeth in more than 125 rows. Its flattened body is covered by hollow spinose sclerites, and a smooth, ventral girdle flanks an extensive mantle cavity. Phylogenetic analyses resolve C. kroegeri as a stem-group aculiferan together with other single-plated forms such as Maikhanella (Siphogonuchites) and Orthrozanclus; Halkieria is recovered closer to the aculiferan crown. These genera document the stepwise evolution of the aculiferan body plan from forms with a single, almost conchiferan-like shell through two-plated taxa such as Halkieria, to the eight-plated crown-group aculiferans. C. kroegeri therefore provides key evidence concerning the long debate about the crown molluscan affinities of sachitids. This new discovery strongly suggests that the possession of only a single calcareous shell plate and the presence of unmineralised sclerites are plesiomorphic (an ancestral trait) for the molluscan crown.
... Non-mineralized fossils from the Burgess Shale Lagerstätte are usually preserved as reflective silicate and carbon films which preserve exquisite details of the morphology of the non-mineralized organisms (Briggs et al. 1994;Orr & Kearns 2011;Gaines et al. 2012;Erwin & Valentine 2013). While this style of preservation occurs at certain horizons at Sirius Passet (Vinther, Eibye-Jacobsen et al. 2011a;Vinther, Smith et al. 2011b), most described fossils from that Lagerstätte are preserved as impressions in mudstone with slight relief, although originally calcareous exoskeletons of the nevadiid trilobite Buenellus higginsi Blaker, 1988, scleritomes of Halkieria evangelista Conway Morris & Peel, 1995 and rare hyoliths (Peel 2010a) usually retain high relief in mouldic preservation, as do the individual spicules of sponges (Botting & Peel 2016). ...
... H. evangelista was a dorsally armoured slug-like animal covered with hundreds of overlocking sclerites and the characteristic anterior and posterior shields (Fig. 5A). Conway Morris & Peel (1995) noted that their largest examined specimen was 71 mm long, almost the same size as the largest figured specimen of Sidneyia? sp. (Fig. 3A). ...
... sp. and most known Sirius Passet arthropods (Pambdelurion is a notable exception), but scavenging of carcasses by arthropods and worms is likely. However, Conway Morris & Peel (1995, Fig. 45c) illustrated an adult specimen of H. evangelista which may have been subject to a predatory attack or scavenging in the trunk region. Anterior shields with injuries (Conway Morris & Peel, 1995, figs. ...
Three dimensional preservation of internal moulds of the digestive tract is a characteristic feature of many arthropods and lobopodians from the Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) of North Greenland and reflects widespread early post-mortem mineralization probably facilitated by endogenous bacteria. The mineralization also preserves pre-mortem gutfills of digestive origin, cololites, providing insight into feeding habits within the Sirius Passet biota. The cololites are described in rare specimens of the arthropods Sidneyia? sp. and Pauloterminus, the annelid worm Phragmochaeta and the palaeoscolecidan worms Chalazoscolex and Xystoscolex. Partly digested material includes fragmentary carapaces of the bivalved arthropod Isoxys volucris and shields of the armoured lophotrochozoan Halkieria evangelista, the iconic Sirius Passet fossil. The presence of sediment in cololites from the small available sample suggests that the described arthropods and worms were omnivores.
... The northern coast successions in Nyeboe Land (Fig. 1.3) are characterized by the trilobite Serrodiscus Richter andRichter, 1941 (Blaker andPeel and Skovsted, in press). The Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) from the lower Buen Formation in western Peary Land ( Fig. 1.1, 1.5) requires special mention as the most significant Cambrian discovery from North Greenland, representing the oldest major Cambrian lagerstätte from Laurentia (Conway Morris et al., 1987;Conway Morris and Peel, 1995;Ineson and Peel, 2011;Peel and Ineson, 2011a, b;Botting and Peel, 2016;Harper et al., 2019). This unique locality with exceptionally preserved fossils lies 12 km to the north of the fossiliferous localities described herein ( Fig. 1.1, 1.5) and was deposited just offshore from the outer degraded edge of the carbonate platform of the Portfjeld Formation, which underlies the more southerly Cambrian successions ( Fig. 1.5). ...
... In contrast, Parkhaev (2008, fig. 3.3) interpreted Ocruranus as the anterior plate of a halkieriid following comparison to material figured by Conway Morris and Peel (1995), with the subapical surface interpreted as posterior. Skovsted et al. (2012) assigned Emargimantus to the Class Helcionelloida Peel, 1991ain which Peel (1991a interpreted this sub-apical surface as posterior. ...
An assemblage of 50 species of small shelly fossils is described from Cambrian Series 2 (Stage 4) strata in North Greenland, the present day northernmost part of the paleocontinent of Laurentia. The fossils are derived from the basal member of the Aftenstjernesø Formation at Navarana Fjord, northern Lauge Koch Land, a condensed unit that accumulated in a sediment-starved outer ramp setting in the transarctic Franklinian Basin, on the Innuitian margin of Laurentia. Most other small shelly fossil assemblages of similar age and composition from North America are described from the Iapetan margin of Laurentia, from North-East Greenland south to Pennsylvania. Trilobites are uncommon, but include Serrodiscus . The Australian bradoriid Spinospitella is represented by a complete shield. Obolella crassa is the only common brachiopod. Hyoliths, including Cassitella , Conotheca , Neogloborilus , and Triplicatella , are abundant and diverse, but most are represented just by opercula. Sclerites interpreted as stem-group aculiferans (sachitids) are conspicuous, including Qaleruaqia , the oldest described paleoloricate, Ocruranus ?, Inughuitoconus n. gen., and Hippopharangites . Helcionelloid mollusks are diverse, but not common; they are associated with numerous specimens of the bivalve Pojetaia runnegari . The fauna compares best with that of the upper Bastion Formation of North-East Greenland, the Forteau Formation of western Newfoundland, and the Browns Pond Formation of New York, but several taxa have a world-wide distribution. Many specimens are encrusted with crystals of authigenic albite. New species: Anabarella ? navaranae , Stenotheca ? higginsi , Figurina ? polaris , Hippopharangites groenlandicus , Inughuitoconus borealis , and Ocruranus ? kangerluk .
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... From the geological perspective, Conway Morris & Peel (1995) were the first to suggest that brachiopods might trace their origin to an unusual and poorly understood extinct group, the halkieriids, which possess multiple skeletal elements of unknown original mineralogy. However, Black dots indicate 100% support; the 91% node should be considered to be collapsed, forming an inarticulated polytomy. ...
... Vinther & Nielsen (2005) concluded that halkieriids were likely to have been calcareous, and very likely to be more closely related to molluscs than to brachiopods. The study by Conway Morris & Peel (1995) triggered a host of other papers on a variety of rather poorly known Lower Cambrian phosphatic fossils referred to generally as tommotiids because of their first appearance in the Tommotian Stage of the Early Cambrian. One genus of tommotiid, Micrina, previously argued to be a halkieriid , was claimed to represent a stem group brachiopod, largely because of microstructural features of the phosphatic sclerites . ...
Earthquakes occur by overcoming fault friction; therefore, quantifying fault resistance is central to earthquake physics. Values for both static and dynamic friction are required, and the latter is especially difficult to determine on natural faults. However, large earthquakes provide signals that can determine friction in situ. The Japan Trench Fast Drilling Project ( JFAST), an Integrated Ocean Discovery Program expedition, determined stresses by collecting data directly from the fault 1–2 years after the 2011 M w 9.1 Tohoku earthquake. Geological, rheological, and geophysical data record stress before, during, and after the earthquake. Together, the observations imply that the shear strength during the earthquake was substantially below that predicted by the traditional Byerlee's law. Locally the stress drop appears near total, and stress reversal is plausible. Most solutions to the energy balance require off-fault deformation to account for dissipation during rupture. These observations make extreme coseismic weakening the preferred model for fault behavior. ▪ Determining the friction during an earthquake is required to understand when and where earthquakes occur. ▪ Drilling into the Tohoku fault showed that friction during the earthquake was low. ▪ Dynamic friction during the earthquake was lower than static friction. ▪ Complete stress drop is possible, and stress reversal is plausible.
Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 48 is May 29, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... showing a veneer of authigenic silica (Strang et al., 2016a) and other mineralized forms such as hyolithids and halkieriids also preserve much of their relief (Conway Morris and Peel, 1995;Peel. 2010a). ...
... In fact, the large majority of documented organisms from the Sirius Passet Lagerstätte have an element of three-dimensional preservation (e.g. Budd 1993Budd , 1999Budd , 2011Conway Morris and Peel 1995;Stein et al. 2010), which is dissimilar to the Burgess Shale-type deposits where organisms have experienced a complete loss of cellular detail and are predominantly preserved in two dimensions (Butterfield 1990(Butterfield , 1995(Butterfield , 2003Gaines et al. 2008, Gaines 2014Briggs 2015). ...
The lower Cambrian Lagerstätte of Sirius Passet, Peary Land, North Greenland, is one of the oldest of the Phanerozoic exceptionally preserved biotas. The Lagerstätte evidences the escalation of numbers of new body plans and life modes that formed the basis for a modern, functionally tiered ecosystem. The fauna is dominated by predators, infaunal, benthic and pelagic, and the presence of abundant nekton, including large sweep-net feeders, suggests an ecosystem rich in nutrients. Recent discoveries have helped reconstruct digestive systems and their contents, muscle fibres, and visual and nervous systems for a number of taxa. New collections have confirmed the complex combination of taphonomic pathways associated with the biota and its potentially substantial biodiversity. These complex animal-based communities within the Buen Formation were associated with microbial matgrounds, now preserved in black mudstones deposited below storm wave base that provide insight into the shift from late Neoproterozoic (Ediacaran) to Cambrian substrates and communities. Moreover, the encasing sediment holds important data on the palaeoenvironment and the water-column chemistry, suggesting that these animal-based communities developed in conditions with very low oxygen concentrations.
... In attempting to establish the course of early trochozoan evolution, including possible links between the annelids and other phyla, various workers have looked to a variety of lower Palaeozoic sclerite-bearing (cataphract) metazoans [26][27][28][29][30][31][32][33][34][35][36][37] . In this regard key taxa include Calvapilosa 28 , Halkieria 26,31 and related forms 29 , Orthrozanclus 32,33 , Oikozetetes 34,37 and Wiwaxia 21,27,35,36 . ...
... If there was such a sclerite configuration, then in the lineage that led to the annelids the two ventro-lateral zones would have ultimately given rise to the biramous arrangement of neurochaetae and notochaetae. These were deployed respectively as locomotory units and a more dorsal thatch-like arrangement that conferred protection 14,24,26 . In an already widely accepted scenario 6,11,24 the transition to a fully fledged annelidan body plan 58 was driven by (a) enhanced motility and, in combination with a body undulation, the development of a stepping pattern of metachronal levers (the parapodia and neurochaetae acting as points d'appui) and (b) in post-Ipoliknus forms (Fig. 3a) the loss of the two zones of dorsal sclerites with any protective role being now adopted by the notochaetae 13,17 . ...
Cambrian annelids are strikingly diverse and reveal important details of annelid character acquisition. Their contribution, however, to a wider understanding of the evolution of the trochozoans (encompassing the annelids as well as such groups as the brachiopods and molluscs) remains limited. Thus the early annelids had been linked to a variety of cataphract Cambrian metazoans, notably Wiwaxia and the halkieriids, but recent work assigns such fossils to stem-group molluscs. Here we report two new annelids from the Lower Cambrian Chengjiang Lagerstätte, South China. Ipoliknus avitus n. gen., n. sp. is biramous with neurochaetae and notochaetae, but significantly also bears dorsal spinose sclerites and dorso-lateral dentate sclerites. Adelochaeta sinensis n. gen., n. sp. is unique amongst Cambrian polychaetes in possessing the rod-like supports of the parapodia known as aciculae. This supports phylogenetic placement of Adelochaeta as sister to some more derived aciculate Palaeozoic taxa, but in contrast Ipoliknus is recovered as the most basal of the stem-group annelids. Sclerites and chaetae of I. avitus are interpreted respectively as the remnants and derivatives of a once more extensive cataphract covering that was a characteristic of more primitive trochozoans. The two sets of chaetae (noto- and neurochaetae) and two sets of sclerites (spinose and dentate) suggest that in a pre-annelid an earlier and more complete scleritome may have consisted of four zones of sclerites. Other cataphract taxa from the Lower Palaeozoic show a variety of scleritome configurations but establishing direct links with such basal annelids as Ipoliknus at present must remain conjectural.
... Reconstruction of isolated sclerites into their original scleritomes is a vital step in the determination of the affinity of Cambrian problematic organisms. The special preservation offered by Lagerstätten has proved invaluable with regard to groups such as the chancelloriids (Bengtson and Collins, 2015) and halkieriids (Conway Morris and Peel, 1995). However, the reconstruction of many other organisms remains speculative and often a mental challenge, as demonstrated, for example, by the multiplated Trachyplax arctica Larsson, Peel, and Högstrom, 2009 that occurs in North Greenland in co-eval strata to those yielding the unrelated Tarimspira plana (Larsson et al., 2009). ...
... The arrangement of individual sclerites and their precise function within the scleritomes are not known. Steiner et al. (2003) speculated that sclerites were closely packed in Tarimspira zhejiangensis with morphotypes B and C located laterally to morphotype D. Interpretation of the sclerites as dorsal armor might promote comparison with well-known but unrelated forms such as the early-middle Cambrian Wiwaxia Walcott, 1911(Slater et al., 2017 or Halkieria Poulsen, 1967 (Conway Morris andPeel, 1995), although the morphology, method of formation, and composition of individual sclerites in the latter are fundamentally different (Smith, 2014;Zhang et al., 2015). Furthermore, there is little direct evidence concerning the orientation of sclerites in Tarimspira. ...
Phosphatic sclerites of the problematic Tarimspira Yue and Gao, 1992 (Cambrian Series 2) recovered by weak acid maceration of limestones display a unique range of mainly strongly coiled morphologies. They were likely organized into multielement scleritomes, but the nature of these is poorly known; some sclerites may have had a grasping function. Tarimspira sclerites grew by basal accretion in an analogous fashion to younger paraconodonts (Cambrian Series 3–4) but lack a basal cavity. Based on proposed homologies, Tarimspira may provide an extension of the early vertebrate paraconodont–euconodont clade back into the early Cambrian. Tarimspira is described for the first time from Laurentia (North Greenland), extending its known range from China and Siberia in Cambrian Series 2. In addition to the type species, Tarimspira plana Yue and Gao, 1992, the Greenland record of Tarimspira includes two morphotypes of a new species, Tarimspira artemi .
UUID: http://zoobank.org /c7c536c8-cdaf-49a9-ae1d-77c392f553fc.
... The modes of fossil preservation appear variable (Stein, Budd, Peel, & Harper, 2013), and the dominant mode is not definitively established. Some fossils of mainly biomineralized taxa are preserved with three-dimensional (3D) relief, while soft-bodied taxa are preserved as two-dimensional (2D) impressions coated by a reflective and-presumably-organic film (Conway Morris & Peel, 1995;Stein, Peel, Siveter, & Williams, 2010;Topper, Greco, Hofmann, Beeby, & Harper, 2018;Vinther, Smith, & Harper, 2011). ...
... For Sirius Passet, interpretations of the palaeodepositional water-column chemistry are few, divergent, and mainly based on macrofossil evidence. For example, the subordinate presence of bioturbation (Ineson & Peel, 2011), a palynology similar to that of other low-oxygen settings (Vidal & Peel, 1993) and the fact that halkieriids (a lophotrochozoan) are preserved somewhat curved, resembling how worms coil up in sudden anoxic conditions (Conway Morris & Peel, 1995), have all been taken to suggest a largely inhospitable water column. Thus, Budd (1995) was the first to acknowledge the challenge of resolving how the soft-tissue Sirius Passet fauna was preserved effectively in situ in an environment that hosted some trace makers. ...
The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional water‐column chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (FeHR/FeT), trace metal behaviour (V/Al), and changes in nitrogen cycling (δ15N). These data, together with Mo/Al and the preservation of organic carbon (TOC), are consistent with a water column that was transiently low in oxygen concentration, or even intermittently anoxic. When compared with the biogeochemical characteristics of modern oxygen minimum zones (OMZs), geochemical and palaeontological data collectively suggest that oxygen concentrations as low as 0.2–0.4 ml/L restricted bioturbation but not the development of a largely nektobenthic community of predators and scavengers. We envisage for the Sirius Passet biota a depositional setting where anoxic water column conditions developed and passed over the depositional site, possibly in association with sea‐level change, and where this early Cambrian biota was established in conditions with very low oxygen.
... Chancelloriids, along with halkieriids, siphogonuchitids, and sachitids, were placed by Bengtson and Missarzhevsky (1981) in the Coeloscleritophora. This proposal was followed by some researchers (e.g., Qian and Bengtson, 1989;Bengtson et al., 1990;Bengtson, 2005;Porter, 2008;Moore et al., 2010), but again rejected by others because of the differences in anatomy between chancelloriids and the halkieriids: the former are cylindrically symmetrical whereas the latter are bilaterally symmetrical (Conway Morris and Peel, 1995;Vinther and Nielsen, 2005). Subsequently, chancelloriids have been considered to be related to tunicates (Mehl, 1996), cnidarians (Randell et al., 2005), mollusks (Conway Morris and Peel, 1995;Vinther and Nielsen, 2005; Conway Morris and Caron, 2007;Vinther, 2009), or to lie elsewhere in the early branches of the Metazoa (Janussen et al., 2002;Sperling et al., 2007). ...
... This proposal was followed by some researchers (e.g., Qian and Bengtson, 1989;Bengtson et al., 1990;Bengtson, 2005;Porter, 2008;Moore et al., 2010), but again rejected by others because of the differences in anatomy between chancelloriids and the halkieriids: the former are cylindrically symmetrical whereas the latter are bilaterally symmetrical (Conway Morris and Peel, 1995;Vinther and Nielsen, 2005). Subsequently, chancelloriids have been considered to be related to tunicates (Mehl, 1996), cnidarians (Randell et al., 2005), mollusks (Conway Morris and Peel, 1995;Vinther and Nielsen, 2005; Conway Morris and Caron, 2007;Vinther, 2009), or to lie elsewhere in the early branches of the Metazoa (Janussen et al., 2002;Sperling et al., 2007). After detailed studies, chancelloriids, with potential eumetazoan plesiomorphy (coelosclerites), were suggested likely to belong to a parayphyletic Coeloscleritophora (Bengtson and Collins, 2015). ...
A large number of well-preserved chancelloriid scleritomes from the Guanshan biota, early Cambrian of Yunnan, China, are described as a new species, Allonnia tenuis n. sp., and provide solid evidence for the original appearance of these enigmatic animals, based on specimens compacted laterally and top-down. With the assistance of a flexible integument, chancelloriids, especially Allonnia from early and middle Cambrian, may have had the ability to partially or completely expand and contract the body, which might have played an important role in feeding. A new metazoan with single-element spines, Nidelric gaoloufangensis n. sp., is also described. Preservation and affinity are discussed. Detailed comparison of the morphology of the body and spines of this metazoan indicate that it shares many similarities with chancelloriids, of which it may be an unusual form.
UUID: http://zoobank.org/2708d95a-1fae-46fc-afea-9707ae97a4d7
... 1d,h and 3a). As with the presumed gut of O. reburrus, this begins slightly posterior to the shell; the gap between the gut and the shell marks a 90° bend in the axis of NIGPAS 164892, reminiscent of an equivalent bend in many Halkieria fossils (see ref. 16 and Fig. 3b). ...
... In view of these similarities, we therefore propose that halkieriids and camenellans may be closely related (Fig. 4). If camenellans are derived from an ancestrally tube-dwelling tommotiid 55 , then a vagrant, slug-like habit would represent an apomorphy of a halkieriid + camenellan clade; alternatively, the halkieriid condition may be ancestral for the tommotiid + brachiopod lineage 16,40 , with the bivalved condition perhaps arising through paedomorphic retention of an ancestral state 41 . ...
Orthrozanclus is a shell-bearing, sclerite covered Cambrian organism of uncertain taxonomic affinity, seemingly representing an intermediate between its fellow problematica Wiwaxia and Halkieria. Attempts to group these slug-like taxa into a single ‘halwaxiid’ clade nevertheless present structural and evolutionary difficulties. Here we report a new species of Orthrozanclus from the early Cambrian Chengjiang Lagerstätte. The scleritome arrangement and constitution in this material corroborates the link between Orthrozanclus and Halkieria, but not with Wiwaxia — and calls into question its purported relationship with molluscs. Instead, the tripartite construction of the halkieriid scleritome finds a more compelling parallel in the camenellan tommotiids, relatives of the brachiopods and phoronids. Such a phylogenetic position would indicate the presence of a scleritome in the common ancestor of the three major trochozoan lineages, Mollusca, Annelida and Brachiozoa. On this view, the absence of fossil Ediacaran sclerites is evidence against any ‘Precambrian prelude’ to the explosive diversification of these phyla in the Cambrian, c. 540–530 million years ago.
... The disarticulated nature of Cambrian skeletal fossils (Small Shelly Fossils (SSFs)) generally obscures their placement in the metazoan tree, seemingly awaiting the discovery of exceptionally preserved specimens to unveil their scleritome structure and biological affinity (e.g. Chen, Hou & Lu, 1989;Conway Morris & Peel, 1995;Skovsted et al., 2008Skovsted et al., , 2009Larsson et al., 2014). Such discoveries are however rare and the majority of Cambrian skeletal fossils continue to float in the taxonomic ether, hindering our understanding of the earliest animal ecosystems. ...
... The discovery of Microdictyon sinicum Chen et al., 1989 and Halkieria evangelista Conway Morris & Peel, 1995 revolutionized the interpretation of Cambrian skeletal assemblages. Both discoveries provided a model for disarticulated sclerites, resulting in a host of skeletal fossils interpreted as constituting cataphract dorsal shields of vermiform bilaterians (Evans & Rowell, 1990;Williams & Holmer, 2002;Li & Xiao, 2004). ...
Mobergellans were one of the first Cambrian skeletal groups to be recognized yet have long remained one of the most problematic in terms of biological function and affinity. Characterized by a disc-shaped, phosphatic sclerite, the most distinctive character of the group is a prominent set of internal scars, interpreted as representing sites of former muscle attachment. Predominantly based on muscle scar distribution, mobergellans have been compared to brachiopods, bivalves and monoplacophorans; however, a recurring theory that the sclerites acted as an operculum remains untested. Rather than correlate the number of muscle scars between taxa, here we focus on the percentage of the inner surface shell area that the scars constitute. We investigate two mobergellan species, Mobergella holsti and Discinella micans, and compare the Cambrian taxa with the muscle scars of a variety of extant and fossil marine invertebrate taxa to test whether the mobergellan muscle attachment area is compatible with an interpretation as operculum. The only skeletal elements in our study with a comparable muscle attachment percentage are gastropod opercula. Complemented with additional morphological information, our analysis supports the theory that mobergellan sclerites acted as an operculum presumably from a tube-living organism. The paucity of tubes co-occurring with mobergellan sclerites could be explained by the transportation and sorting of detached opercula, while the corresponding tube remained attached to substrata in shallower water. The operculum perhaps performed a similar role to that seen in serpulid annelids and in neritid gastropods sealing the living chamber of the organism to avoid desiccation or for protection.
... Moreover, several extinct lophotrochozoans also show the presence of biomineralized skeletons with various degrees of structural integration-e.g., Machaeridia (considered as extinct stem-group annelids), Cotyledion (a stem-group Kamptozoan), tommotiids (a probably paraphyletic assemblage of stem and crown group lophophorates) and hyoliths (an extinct clade with possible affinity to lophophorates) were all equipped with either sclerites that build the external armor or bona fide shells (e.g., Guo et al., 2022;Li et al., 2019;Moysiuk et al., 2017;Parry et al., 2014Parry et al., , 2019Skovsted et al., 2008Skovsted et al., , 2011Sun et al., 2018;Taylor et al., 2010;Vinther et al., 2008;Zhang et al., 2013). Based on the phylogenetic distribution of biomineralizing capacities and the existence of extinct biomineralized close relatives of contemporary soft-bodied taxa, some authors suggested that biomineralization was already present in the common lophotrochozoan ancestor (e.g., Conway Morris & Peel, 1995;Li et al., 2019;Taylor et al., 2010;Zhang et al., 2013). This idea recently got support from developmental and gene-expression studies that showed the presence of an ancestral biomineralizing toolkit, shared by mollusks and brachiopods (Jackson et al., 2015;Luo et al., 2015;Wernström et al., 2022). ...
Phoronids, together with brachiopods and bryozoans, form the animal clade Lophophorata. Modern lophophorates are quite diverse-some can biomineralize while others are soft-bodied, they could be either solitary or colonial, and they develop through various eccentric larval stages that undergo different types of metamorphoses. The diversity of this clade is further enriched by numerous extinct fossil lineages with their own distinct body plans and life histories. In this review, I discuss how data on phoronid development, genetics, and morphology can inform our understanding of lophophorate evolution. The actinotrocha larvae of phoronids is a well documented example of intercalation of the new larval body plan, which can be used to study how new life stages emerge in animals with biphasic life cycle. The genomic and embryonic data from phoronids, in concert with studies of the fossil lophophorates, allow the more precise reconstruction of the evolution of lophophorate biomineralization. Finally, the regenerative and asexual abilities of phoronids can shed new light on the evolution of coloniality in lophophorates. As evident from those examples, Phoronida occupies a central role in the discussion of the evolution of lophophorate body plans and life histories.
... The cone-shaped C and D sclerite morphotypes of L. bornholmiensis are more difficult to compare to the laterally compressed C sclerites of Dailyatia, and their position in the scleritome remains uncertain. However, the slender D type sclerite are broadly comparable to spiniform sclerites arranged along the lateral margins in some non-tommotiid scleritome bearing taxa such as Halkieria (Conway Morris & Peel 1995), and could perceivably have had a similar arrangement in Lapworthella. ...
The Camenellan tommotiid Lapworthella bornholmiensis is systematically revised based on the original type material and collections of Small Shelly Fossils at the Swedish Museum of Natural History. The species is clearly differentiated from all other species of Lapworthella by its unique surface ornamentation. Variability in sclerite shape is analyzed among the 39 specimens and four sclerite morphotypes are recognized: bilaterally subsymmetrical A sclerites with straight apertural margin and subrectangular to subelliptical cross-section; asymmetrical B sclerites with oblique to curved apertural margin and subrectangular to subelliptical cross-section; asymmetrical C sclerites with one concave surface resulting in elliptical to sub-triangular cross section; elongated asymmetrical D sclerites with subcircular cross section. The C sclerites are further divided into two sub-types. The sclerite morphotypes of Lapworthella bornholmiensis allow a detailed comparison with other lapworthellid taxa and we identify a pattern of recurring sclerite morphotypes across a range of species, allowing a new understanding of the lapworthellid scleritome structure. The stratigraphic range of Lapworthella bornholmiensis includes the Cambrian Stage 4 Gislöv Formation, the Wuliuan-Drumian Forsemölla and Exsulans Limestones in the Alum Shale Formation and Guzhangian limestone fill in Proterozoic basement fissures in Bohuslän, making this long ranging species the youngest known tommotiid in the fossil record.
... Indeed, Zhao et al. 36 rejected a sachitid affinity for Halkieria 33 allying it and Orthozanclus to the camenellans (compare Fig. 7). To them and others 43 , this similarity reflects brachiopods and molluscs having descended from a slug-like common ancestor with a dorsal, serially organized scleritome that may or may not have been biomineralized. They consider but dismiss the challenges of this hypothesis, including the conflicting mineralogies of sachitid and tommotiid sclerites. ...
Fossilized invertebrate embryonic and later developmental stages are rare and restricted
largely to the Ediacaran-Cambrian, providing direct insight into development during the
emergence of animal bodyplans. Here we report a new assemblage of eggs, embryos
and bilaterian post-embryonic developmental stages from the early Cambrian Salanygol
Formation of Dzhabkan Microcontinent of Mongolia. The post-embryonic developmental
stages of the bilaterian are preserved with cellular fidelity, possessing a series of bilaterally
arranged ridges that compare to co-occurring camenellan sclerites in which the initial growth
stages retain the cellular morphology of modified juveniles. In this work we identify these
fossils as early post-embryonic developmental stages of camenellans, an early clade of stembrachiopods,
known previously only from isolated sclerites. This interpretation corroborates
previous reconstructions of camenellan scleritomes with sclerites arranged in medial and
peripheral concentric zones. It further supports the conjecture that molluscs and brachiopods
are descended from an ancestral vermiform and slug-like bodyplan.
... Chancelloriids were once lumped with halkieriids, sachitids, and siphogonuchitids in the Coeloscleritophora (Bengtson and Missarzhevsky, 1981), largely based on isolated sclerites. However, the discovery of articulated specimens of some of the "coeloscleritophorans" revealed marked differences in body organization and lifestyle that undermined the validity of this taxonomic grouping (Conway Morris and Peel, 1995;Conway Morris and Chapman, 1996). Later, investigations on sclerite microstructures shed light on the phylogenetic relationships of chancelloriids with other metazoans. ...
As extinct animals that flourished during the Cambrian explosion, chancelloriids have a unique body plan lacking guts but with a flexible integument and a suite of star-shaped, hollow sclerites. Due to this body plan, along with the paucity of knowledge on sclerite biomineralization, the phylogenetic position of chancelloriids within the Metazoa is still controversial. Integration of analyses of diverse fossils from Cambrian stage 2 to the Wuliuan Stage of China and Australia indicates that chancelloriid sclerites possess an encasement-like organic layer and a fibrous aragonitic layer. The organic layer is inferred to be a specialized trait derived from the epidermal integument of the animal body. The sclerites were likely biomineralized by using the outer organic layer as a template to absorb cations and precipitate crystal nuclei, reflecting a strategy adopted by a range of eumetazoans with a developed epidermis. Therefore, the hypothesis that chancelloriids represent an epitheliozoan-grade animal and an early explorer of template-based biomineralization is supported.
... Cambrian 'small shelly faunas' or at least, specific members of this fauna, such as molluscs, are often interpreted to be small organisms with small shells (Pojeta, 1981;Runnegar and Pojeta, 1985), or as individual small sclerites of larger animals with multi-element scleritomes, i.e. chancelloriids (Bengtson and Missarzhevsky, 1981;Bengtson and Hou, 2001;Janussen et al., 2002;Randell et al., 2005;Bengtson and Collins, 2015) and halkieriids (Conway Morris and Peel, 1995;Vinther and Nielsen, 2005). Indeed, small shell size has been identified as a factor in this style of preservation (Creveling et al., 2014a;Dattilo et al., 2016;Pruss et al., 2018). ...
Carbonate fluorapatite-filled millimeter-scale microsteinkerns are a key element of the “Small Shelly Fossil” (SSF) fauna generally associated with the late Proterozoic–Cambrian. The purported disappearance of these fossils and this style of phosphatic preservation during the Cambrian Stage 2 “Botomian extinction” has been linked to changes in ocean chemistry and/or changes to the physical environment due to the evolution of metazoans, as well to the changing role of metazoans in the marine environment. Through a qualitative meta-analysis of existing literature, we document a broader temporal distribution for SSF-style preservation than previously recognized. We examine these occurrences for common patterns of depositional conditions, and we offer a conceptual model for both the origin of the phosphatic microsteinkerns and their eventual concentration in certain sediments, based on known biogeochemical diagenetic processes of authigenic calcium fluorapatite precipitation (phosphogenesis) and subsequent concentration of phosphatic sedimentary particles. This polycyclic phosphogenic condensation (PPC) model makes predictions as to how and where this form of preservation might occur in Cambrian and non-Cambrian marine strata alike.
... (lophotrochozoans) , , , [14] . , Geogina ...
... These concerns aside however, if machaeridians are stemgroup annelids [10], then a common annelid-brachiopod ancestor with tommotiid-like sclerites could conceivably be proposed, with sclerites becoming modified to machaeridian shell plates and then ultimately lost later in the annelid stem lineage. A scleritomous ancestor for annelids, molluscs and brachiopods has previously been discussed, such as in the hypothesis of Conway Morris and Peel [16], which sought to link halkieriids and Wiwaxia to the stem lineages of annelids, brachiopods and molluscs. Given that these three phyla are closely related, the hypothesis of a common origin of machaeridians and other scleritomous fossil taxa deserves some attention, especially considering the tumultuous history of the classification of scleritomous Cambrian and Ordovician animals. ...
Machaeridians are Palaeozoic animals that are dorsally armoured with serialized, imbricating shell plates that cover or enclose the body. Prior to the discovery of an articulated plumulitid machaeridian from the Early Ordovician of Morocco that preserved unambiguous annelid characters (segmental parapodia with chaetae), machaeridians were a palaeontological mystery, having been previously linked to echinoderms, barnacles, tommotiids (putative stem-group brachiopods) or molluscs. Although the annelid affinities of machaeridians are now firmly established, their position within the phylum and relevance for understanding the early evolution of Annelida is less secure, with competing hypotheses placing Machaeridia in the stem or deeply nested within the crown group of annelids. We describe a scleritome of Plumulites bengtsoni from the Fezouata Formation of Morocco that preserves an anterior jaw apparatus consisting of at least two discrete elements that exhibit growth lines. Although jaws have multiple independent origins within the annelid crown group, comparable jaws are present only within Phyllodocida, the clade that contains modern aphroditiforms (scaleworms and relatives). Phylogenetic analysis places a monophyletic Machaeridia within the crown group of Phyllodocida in total-group Aphroditiformia, consistent with a common origin of machaeridian shell plates and scaleworm elytrae. The inclusion of machaeridians in Aphroditiformia truncates the ghost lineage of Phyllodocida by almost a hundred million years.
... Halkieria evangelista, Sirius Passet, Greenland Conway Morris and Peel (1995) Orthrozanclus elongata, Chengjiang Zhao et al. (2017) Orthrozanclus reburrus, Burgess Shale Conway Spence Shale halkieriid, Utah Second shell-anterior end? No differences in trunk cuticle. ...
This single specimen from the Spence Shale is the first from Utah and may be the first from anywhere in the U.S. It is missing dorsal sclerites and the presumed anterior end, however, the remaining shell and vermiform body with pyrite in the cuticle point to affinities with the other known halkieriids.
Note: I was not able to present this poster due to an injury accident, however, I wanted to let it be viewed. I welcome responses and criticism.
... This interpretation applies not only to the Burgess Shale material analysed here, but also to many illustrated trace fossil -body fossil associations in other Burgess Shale-type deposits (e.g. [20,76]). However, those trace fossil-body fossil associations that display relatively high densities of trace fossils and involve higher ichnodiversity or show particular morphologic patterns recording confinement (e.g. ...
The association of trace fossils and non-biomineralized carapaces has been reported from Cambrian Lagerstätten worldwide, but the abundance, ichnodiversity, taphonomy and ecological significance of such associations have yet to be fully investigated. Two main end-member hypotheses are explored based on the study of a relatively wide variety of trace fossils preserved associated to Tuzoia carapaces from the middle Cambrian Burgess Shale in British Columbia. In the ecological Tuzoia garden hypothesis, the bacterially enriched surface of carapaces provides opportunities for intricate ecologic interactions among trophic levels. In the taphonomic shielding hypothesis, the trace fossil–carapace association results from preferential preservation of traces as controlled by compaction independent of any association in life. In an attempt to better understand the role of the carapace as a medium for preservation of trace fossils and to evaluate the effects of mechanical stress related to burial, a numerical model was developed. Results indicate that the carapace can shield underlying sediment from mechanical stress for a finite time, differentially protecting trace fossils during the initial phase of burial and compaction. However, this taphonomic model alone fails to fully explain relatively high-density assemblages displaying a diversity of structures spatially confined within the perimeter of carapaces or branching patterns recording re-visitation.
... Intact calcareous sachitid scleritomes are considered to belong to a bilateral motile organism that possessed a radula and sclerites with a branching, aesthete type of canal system found in some molluscs [48][49][50] . Complete sachitid scleritomes from the Early Ordovician are recognized as stem-group aculiferan molluscs 51 . ...
The dynamics of how metazoan phyla appeared and evolved – known as the Cambrian Explosion – remains elusive. We present a quantitative analysis of the temporal distribution (based on occurrence data of fossil species sampled in each time interval) of lophotrochozoan skeletal species (n = 430) from the terminal Ediacaran to Cambrian Stage 5 (~545 – ~505 Million years ago (Ma)) of the Siberian Platform, Russia. We use morphological traits to distinguish between stem and crown groups. Possible skeletal stem group lophophorates, brachiopods, and molluscs (n = 354) appear in the terminal Ediacaran (~542 Ma) and diversify during the early Cambrian Terreneuvian and again in Stage 2, but were devastated during the early Cambrian Stage 4 Sinsk extinction event (~513 Ma) never to recover previous diversity. Inferred crown group brachiopod and mollusc species (n = 76) do not appear until the Fortunian, ~537 Ma, radiate in the early Cambrian Stage 3 (~522 Ma), and with minimal loss of diversity at the Sinsk Event, continued to diversify into the Ordovician. The Sinsk Event also removed other probable stem groups, such as archaeocyath sponges. Notably, this diversification starts before, and extends across the Ediacaran/Cambrian boundary and the Basal Cambrian Carbon Isotope Excursion (BACE) interval (~541 to ~540 Ma), ascribed to a possible global perturbation of the carbon cycle. We therefore propose two phases of the Cambrian Explosion separated by the Sinsk extinction event, the first dominated by stem groups of phyla from the late Ediacaran, ~542 Ma, to early Cambrian stage 4, ~513 Ma, and the second marked by radiating bilaterian crown group species of phyla from ~513 Ma and extending to the Ordovician Radiation.
... Irrespective of whether or not Kimberella is an early stem-line mollusc and whether or not other debated fossils such as Acaenoplax, Wiwaxia, Halkieria, or the newly described Calvapilosa belong to the molluscan stem, are members of later-branching molluscan sublineages, or do not constitute molluscs at all (Conway Morris, 1985;Butterfield, 1990; Conway Morris & Peel, 1990, 1995Steiner & Salvini-Plawen, 2001;Sutton et al., 2001Sutton et al., , 2004Scheltema & Ivanov, 2002;Vinther & Nielsen, 2005;Conway Morris & Caron, 2007;Telford & Budd, 2011;Vinther, 2014;Parkhaev, 2017;Vinther et al., 2017), a sound inference of molluscan evolutionary history involving ground pattern reconstruction requires a well-supported phylogenetic framework . While this has traditionally been a major gap in molluscan research, both concerning intraspecific relationships of class-level taxa but also with respect to unresolved molluscan sister group relationships (Wanninger, 2009;Haszprunar & Wanninger, 2012), recent large-scale phylogenomic analyses (Kocot et al., 2011;Smith et al., 2011) lend hope that some emerging phylogenetic patterns within the phylum will consolidate and will provide a long-sought base for addressing questions concerned with molluscan origins and phenotypic diversification. ...
Molluscs are extremely diverse invertebrate animals with a rich fossil record, highly divergent life cycles, and considerable economical and ecological importance. Key representatives include worm‐like aplacophorans, armoured groups (e.g. polyplacophorans, gastropods, bivalves) and the highly complex cephalopods. Molluscan origins and evolution of their different phenotypes have largely remained unresolved, but significant progress has been made over recent years. Phylogenomic studies revealed a dichotomy of the phylum, resulting in Aculifera (shell‐less aplacophorans and multi‐shelled polyplacophorans) and Conchifera (all other, primarily uni‐shelled groups). This challenged traditional hypotheses that proposed that molluscs gradually evolved complex phenotypes from simple, worm‐like animals, a view that is corroborated by developmental studies that showed that aplacophorans are secondarily simplified. Gene expression data indicate that key regulators involved in anterior–posterior patterning (the homeobox‐containing Hox genes) lost this function and were co‐opted into the evolution of taxon‐specific novelties in conchiferans. While the bone morphogenetic protein (BMP)/decapentaplegic (Dpp) signalling pathway, that mediates dorso‐ventral axis formation, and molecular components that establish chirality appear to be more conserved between molluscs and other metazoans, variations from the common scheme occur within molluscan sublineages. The deviation of various molluscs from developmental pathways that otherwise appear widely conserved among metazoans provides novel hypotheses on molluscan evolution that can be tested with genome editing tools such as the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeats‐associated protein9) system.
... Definitely at that time the forms with a typical diplacophoran set of dorsal armoring existed, i.e., a pair of shell plates on the head and tail regions, such as in the group of Ocruranus-Eohalobia (Parkhaev, 2008, text-fig. 3.3;Vendrasco et al., 2009;Parkhaev and Demidenko, 2010), and in the genera Halkieria (Conway Morris and Peel, 1995) and Oikozetetes (Conway Paterson et al., 2009). In addition to the terminal plates these fossils had numerous blade-like sclirites in-between (Pl. ...
The paper gives an overview of the modern hypotheses on the origin of the phylum Mollusca and the formation of its main classes. The Cambrian stage of molluscan evolution is characterized based on the paleontological material. The doubtfulness of assignment of the Precambrian (Vendian) soft-bodied fossil Kimberella to mollusks is argued. Judging from the interpretation of the morphologically diverse Cambrian fossils, it is suggested that the classes Polyplacophora, Monoplacophora, Gastropoda and Bivalvia formed already near the Precambrian-Cambrian boundary, i.e., from the beginning of the paleontologically documented evolutionary history of the phylum, whereas the assumption of the later origin of these taxa is unconvincing. The remaining classes of mollusks arose later, i.e., Cephalopoda, in the Late Cambrian; Scaphopoda, in the Ordovician; and Aplacophora, in the Silurian.
... Although the taxonomic affinities of many disarticulated sclerites remain unresolved, the discovery of extraordinarily well-preserved, articulated, multiplated, soft-bodied specimens in Burgess Shale-type Lagerstätten can provide significant insights into the functional morphology and phylogenetic position of SSF taxa. Perhaps the most influential examples are the descriptions of Microdictyon sinicum Chen, Hou, and Lu, 1989 from the Chengjiang Biota (Chen et al., 1995), Halkieria evangelista Conway Morris and Peel, 1995from North Greenland (Conway Morris and Peel, 1990Vinther and Nielsen, 2005), and Wiwaxia corrugata (Matthew, 1899) from the Burgess Shale (Conway Morris, 1985;Smith, 2014). ...
Disarticulated net-like plates of the lobopod Microdictyon had a near cosmopolitan distribution from the early to middle Cambrian but are yet to be documented from the North China Platform. Here we report isolated plates of Microdictyon from the lower Cambrian Xinji Formation (Stage 4, Series 2) of the North China Platform, extending the paleogeographic distribution of Microdictyon in the early Cambrian. The plates of Microdictyon from the Xinji Formation are similar to those of other species established on the basis of isolated plates but do bear some new characters, such as mushroom-shaped nodes with a single inclined platform-like apex and an upper surface that displays radial lines. However, the plates documented here are left under open nomenclature due to inadequate knowledge of intraspecific and ontogenetic variation and low specimen numbers. Through comparison of the node shapes of the isolated plates of different Microdictyon species, we consider that low mushroom-shaped nodes could be a primitive and conservative character of Microdictyon while tall mushroom-shaped nodes may be a derived character. Subtle differences in shape and number of node apices may also represent intraspecific or ontogenetic variation.
... An alternative phylogenetic interpretation by Bengtson (1992) is based on evidence for maikhanellids merging siphogonuchitid sclerites into their shells. Based on younger Wiwaxia-like organisms with non-mineralized scleritomes and on complete scleritomes of halkieriids, which have two terminal shells and rows of intermediate sclerites (Conway Morris and Peel 1995), maikhanellids were assigned to a phylum-level, lopho-trochozoan stem-group called Halwaxiida Conway Caron, 2007. Butterfield (2006) suggested, however, that Wiwaxia and halkieriids have markedly different sclerite construction and composition and cannot be assigned to one phyletic grouping. ...
Assemblages of mineralized skeletal fossils are described from limestone rocks of the lower Cambrian Nemakit-Daldyn, Medvezhya, Kugda-Yuryakh, Manykay, and lower Emyaksin formations exposed on the western and eastern flanks of the Anabar Uplift of the northern Siberian Platform. The skeletal fossil assemblages consist mainly of anabaritids, molluscs, and hyoliths, and also contain other taxa such as Blastulospongia, Chancelloria, Fomitchella, Hyolithellus, Platysolenites, Protohertzina, and Tianzhushanella. The first tianzhushanellids from Siberia, including Tianzhushanella tolli sp. nov., are described. The morphological variation of Protohertzina anabarica and Anabarites trisulcatus from their type locality is documented. Prominent longitudinal keels in the anabaritid Selindeochrea tripartita are demonstrated. Among the earliest molluscs from the Nemakit-Daldyn Formation, Purella and Yunnanopleura are interpreted as shelly parts of the same species. Fibrous microstructure of the outer layer and a wrinkled inner layer of mineralised cuticle in the organophosphatic sclerites of Fomitchella are reported. A siliceous composition of the globular fossil Blastulospongia is reported herein and a possible protistan affinity similar to Platysolenites is discussed. New carbon isotope data facilitate correlation both across the Anabar Uplift and with the Terreneuvian Series of the IUGS chronostratigraphical scheme for the Cambrian System. The base of Cambrian Stage 2 is provisionally placed herein within the Fortunian‒Cambrian Stage 2 transitional interval bracketed by the lowest appearance of Watsonella crosbyi and by a slightly higher horizon at the peak of carbon isotope excursion Iʹ from western flank of the Anabar Uplift. Correlation across the Siberian Platform of the fossiliferous Medvezhya and lower Emyaksin formations showing δ13Ccarb excursion Iʹ with the upper Sukharikha Formation containing excursion 5p and upper Ust’-Yudoma Formation containing excursion I is supported herein.
... Halkieria evangelista, the only known articulated halkieriid animal has a complicated scleritome incorporating as many as 2000 small, spine or bladelike sclerites with internal cavities as well as two larger mollusc-or brachiopod-like shells, one at each end of the slug-like body (Conway Morris & Peel 1995;Vinther & Nielsen 2005). The sclerites of halkieriids are calcareous in composition and are hollow with a restricted basal foramen and they show no indications of incremental growth (Bengtson & Missarzhevsky 1981;Porter 2008), unlike the larger shells that exhibit concentric growth lines. ...
The camenellan tommotiid Dailyatia is one of the most common fossils in shallow water carbonates from Cambrian Stages 2-4 in South Australia (Arrowie and Stansbury basins). Six species of Dailyatia are documented and new terminology for describing camenellan sclerites is introduced. Dailyatia sclerites are found in three fundamental sclerite types (A-C), each of which may be present in one to three sub-types depending on species. The previously described species Dailyatia ajax Bischoff 1976 and D. macroptera (Tate 1892) are revised and four additional species are described for the first time from South Australia. These include D. odyssei Evans & Rowell 1990, previously known only from Antarctica, and two new species; D. bacata sp. nov. and D. helica sp. nov. as well as a species left under open nomenclature. Two of the recognised species (D. macroptera and D. helica) occur in two different ecophenotypic variants. Species and variants are defined by differences in sclerite types present in the scleritome, sclerite morphology and ornament. The sclerites of Dailyatia are finely laminated with distal expansion of laminae supporting the prominent concentric ribs. The external surface is covered by a fine reticulate network which indicates that the sclerites were at least partly embedded in soft integument. The pattern of incremental growth reveals specific initial and possible gerontic growth stages with unique surface sculptures. Evidence of physical damage and growth disturbances is common in Dailyatia sclerites and many specimens reveal preferential abrasion of the apex. Apical canals are present in all sclerites and are connected to specialised internal apical structures.
The internal surface of the sclerites in most species reveals raised platforms and depressed, scar like areas forming unique patterns in each sclerite type, presumably representing muscular attachment. Two specimens revealing ontogenetic fusion of Dailyatia sclerites have been recovered. Based on all available evidence, a new reconstruction of the Dailyatia scleritome is proposed. In the reconstruction, a central row of A and paired B sclerites is flanked on both sides by one or two lateral rows of C sclerites. The exact number of sclerites may vary between species. This reconstruction is based on an assumed slug-like bodyplan and the Dailyatia animal is considered to be a vagrant, benthic animal living in and around archaeocyathan-microbial buildups and in other shallow water carbonate environments.
... With their single, bilaterally symmetrical shell, the merismoconchs are unlike those of the genus Halkieria Poulsen, 1967 (Runnegar, 19(6), the shells which are very complex as shown by the generic diagnosis given by Conway Morris and Peel (1995): "Siculates form imbricating rows, each consisting of a fan-like array, apparently arising from a lobe. Imbricated cultrates flank lateral, anterior and posterior regions, increasing in size adaxially. ...
... We present analyses of 80 taxa and 192 morphological characters, including a sample of 62 extant annelids, five outgroups from within Lophotrochozoa and 16 Palaeozoic fossil terminals. Fossil taxa include polychaetes, sipunculans and the 'halwaxiids', the latter a problematic (and probably non-monophyletic) assemblage of lophotrochozoan fossils that have been interpreted as stem and/or crown-group representatives of brachiopods, molluscs and annelids [39,40]. Extant taxa include those resolved at the base of the tree in phylogenomic analyses [12], namely Oweniidae, Magelonidae, Chaetopteridae and Sipuncula, including the Cambrian fossil sipunculans described by Huang et al. [41]. ...
As a result of their plastic body plan, the relationships of the annelid worms and even the taxonomic makeup of the phylum have long been contentious. Morphological cladistic analyses have typically recovered a monophyletic Polychaeta, with the simple-bodied forms assigned to an early-diverging clade or grade. This is in stark contrast to molecular trees, in which poly-chaetes are paraphyletic and include clitellates, echiurans and sipunculans. Cambrian stem group annelid body fossils are complex-bodied polychaetes that possess well-developed parapodia and paired head appendages (palps), suggesting that the root of annelids is misplaced in morphological trees. We present a reinvestigation of the morphology of key fossil taxa and include them in a comprehensive phylogenetic analysis of annelids. Analyses using probabilistic methods and both equal-and implied-weights parsimony recover paraphyletic polychaetes and support the conclusion that echiurans and clitellates are derived polychaetes. Morphological trees including fossils depict two main clades of crown-group annelids that are similar, but not identical, to Errantia and Sedentaria, the fundamental groupings in transcriptomic analyses. Removing fossils yields trees that are often less resolved and/or root the tree in greater conflict with molecular topologies. While there are many topological similarities between the analyses herein and recent phylogenomic hypotheses, differences include the exclusion of Sipuncula from Annelida and the taxa forming the deepest crown-group divergences.
The Precambrian-Cambrian transition saw the burgeoning of diverse skeletal organisms (“small shelly fossils”), represented in the fossil record by spicules, tubes, tests, conchs, shells, and a variety of sclerites and ossicles. Whereas calcareous biomineralization as such may have been facilitated by changes in ocean chemistry at this time, the utilization of biominerals in mineralized skeletons is a different process. The massive appearance of skeletons is most likely an epiphenomenon of the general radiation of body plans and tissues. The “choice” of biominerals (mainly calcium carbonates, calcium phosphates, and silica) may reflect the environmental conditions under which the particular skeleton first evolved.
The Sirius Passet Lagerstätte of North Greenland is one of the oldest records of soft-bodied metazoan-dominated ecosystems from the early Cambrian. The Lagerstätte site itself is restricted to just a single c. 1-km-long outcrop located offshore from the shelf margin, in an area affected by metamorphic alteration during the Ellesmerian Orogeny (Devonian-Early Carboniferous). The recent recovery of small carbonaceous fossils (SCFs) to the south, in areas that escaped the effects of this deformation, has substantially expanded the known coverage of organic preservation into shallower water depositional settings in this region. Here, we describe additional SCF assemblages from the siliciclastic shelf succession of the Buen Formation (Cambrian Series 2, stages 3-4; c. 515 Ma), expanding the previously documented SCF biota. Newly recovered material indicates a rich diversity of non-mineralizing metazoans, chiefly represented by arthropod remains. These include the filtering and grinding elements of a sophisticated crustacean feeding apparatus (the oldest crustacean remains reported to date), alongside an assortment of bradoriid sclerites, including almost complete , 3D valves, which tie together a number of SCFs previously found in isolation. Other metazoan remains include various trilobite cuticles, diverse scalidophoran sclerites, and a range of metazoan fragments of uncertain affinity. This shallower water assemblage differs substantially from the Sirius Passet biota, which is dominated by problematic euarthropod stem-group members and sponges. Although some of these discrepancies are attributable to taphonomic or temporal factors, these lateral variations in taxonomic composition also point to significant palaeoenvironmental and/or palaeoecological controls on early Cambrian metazoan communities .
The geological development of Greenland spans a period of nearly 4 Ga, from Eoarchaean to the Quaternary. Greenland is the largest island on Earth with a total area of 2 166 000 km2, but only c. 410 000 km2 are exposed bedrock, the remaining part being covered by a major ice sheet (the Inland Ice) reaching over 3 km in thickness. The adjacent offshore areas underlain by continental crust have an area of c. 825 000 km2. Greenland is dominated by crystalline rocks of the Precambrian shield, which formed during a succession of Archaean and Palaeoproterozoic orogenic events and stabilised as a part of the Laurentian shield about 1600 Ma ago. The shield area can be divided into three distinct types of basement provinces: (1) Archaean rocks (3200–2600 Ma old, with local older units up to> 3800 Ma) that were almost unaffected by Proterozoic or later orogenic activity; (2) Archaean terrains reworked during the Palaeoproterozoic around 1900–1750 Ma ago; and (3) terrains mainly composed of juvenile Palaeoproterozoic rocks (2000–1750 Ma in age). Subsequent geological developments mainly took place along the margins of the shield. During the Proterozoic and throughout the Phanerozoic major sedimentary basins formed, notably in North and North-East Greenland, in which sedimentary successions locally reaching 18 km in thickness were deposited. Palaeozoic orogenic activity affected parts of these successions in the Ellesmerian fold belt of North Greenland and the East Greenland Caledonides; the latter also incorporates reworked Precambrian crystalline basement complexes. Late Palaeozoic and Mesozoic sedimentary basins developed along the continent–ocean margins in North, East and West Greenland and are now preserved both onshore and offshore. Their development was closely related to continental break-up with formation of rift basins. Initial rifting in East Greenland in latest Devonian to earliest Carboniferous time and succeeding phases culminated with the opening of the North Atlantic Ocean in the late Paleocene. Sea-floor spreading was accompanied by extrusion of Palaeogene (early Tertiary) plateau basalts in both central West and central–southern East Greenland. During the Quaternary Greenland was almost completely covered by ice, and the present day Inland Ice is a relic from the Pleistocene ice ages. Vast amounts of glacially eroded detritus were deposited on the continental shelves around Greenland. Mineral exploitation in Greenland has so far encompassed cryolite, lead-zinc, gold, olivine and coal. Current prospecting activities in Greenland are concentrated on gold, base metals, platinum group elements, molybdenum, iron ore, diamonds and lead-zinc. Hydrocarbon potential is confined to the major Phanerozoic sedimentary basins, notably the large basins offshore North-East and West Greenland. While reserves of oil or gas have yet to be found, geophysical data combined with discoveries of oil seeps onshore have revealed a considerable potential for offshore oil and gas.
Biomineralized skeletons are widespread in animals, and their origins can be traced to the latest Ediacaran or early Cambrian fossil record, in virtually all animal groups. The origin of animal skeletons is inextricably linked with the diversification of animal body plans and the dramatic changes in ecology and geosphere–biosphere interactions across the Ediacaran–Cambrian transition. This apparent independent acquisition of skeletons across diverse animal clades has been proposed to have been driven by co‐option of a conserved ancestral genetic toolkit in different lineages at the same time. This ‘biomineralization toolkit’ hypothesis makes predictions of the early evolution of the skeleton, predictions tested herein through a critical review of the evidence from both the fossil record and development of skeletons in extant organisms. Furthermore, the distribution of skeletons is here plotted against a time‐calibrated animal phylogeny, and the nature of the deep ancestors of biomineralizing animals interpolated using ancestral state reconstruction. All these lines of evidence point towards multiple instances of the evolution of biomineralization through the co‐option of an inherited organic skeleton and genetic toolkit followed by the stepwise acquisition of more complex skeletal tissues under tighter biological control. This not only supports the ‘biomineralization toolkit’ hypothesis but also provides a model for describing the evolution of complex biological systems across the Ediacaran–Cambrian transition.
Chancelloriids are a poorly understood group of phylogenetically problematic Cambrian metazoans; complete specimens show they were sessile, radially symmetrical, club‐shaped organisms covered with sclerites in the form of rosettes of spines. While isolated sclerites are common components of Cambrian shelly assemblages, they have been relatively little studied. We describe chancelloriid sclerites from a series of nine sections spanning the upper Dyeran to lower Delamaran stages (latest Stage 4 to perhaps basal Wuliuan) from the Pioche–Caliente region of east‐central Nevada, USA. Acid maceration of samples from the Combined Metals, Comet Shale and Susan Duster Limestone members of the Pioche Formation yielded more than 2000 sclerites. Based on careful examination of these sclerites and statistical analyses of co‐occurring sclerite types, we distinguish six species, each with a restricted stratigraphic range. Chancelloria impar Moore sp. nov. is the dominant species in most upper Dyeran samples. Archiasterella cometensis Moore sp. nov. and A. auriculata Moore sp. nov. are rare in the upper Dyeran but abundant in the lowest Delamaran; A. uncinata Moore sp. nov. and C. lilioides Moore sp. nov. replace these in younger samples. A. auriculata is noteworthy for sharing features with species of both Archiasterella and Chancelloria. These results provide further support for the taxonomic tractability and biostratigraphical utility of chancelloriid sclerites; large collections from single horizons allow intraspecific variability to be assessed and species to be distinguished. Our results document a taxonomic turnover in chancelloriids at the Dyeran–Delamaran boundary, showing that not only trilobites were affected at this time.
The diverse metazoan fauna from the upper member of the Buen Formation of North Greenland is described as a complement to published descriptions of the exceptionally preserved fauna of the Sirius Passet Lagerstätte which occurs in the lowest beds of the formation. Considered together with organic‐walled microfossils, which are absent from the Sirius Passet Lagerstätte on account of regional metamorphism, the fauna from the upper member provides an extended picture of the Buen Formation biota (Cambrian, Series 2, Stages 3–4; Montezuman–Dyeran of Laurentian usage). Although dominated numerically by specimens of the olenelline trilobites Limniphacos and Mesolenellus, the oldest assemblages (Montezuma–Dyeran boundary) from the upper member of the Buen Formation are characterized by a high diversity of hyoliths which often occur as partial associations of conch, operculum and helens in the dark mudstones; hyoliths are rare in the Sirius Passet Lagerstätte. Sponges are rare in the upper Buen Formation but diverse at Sirius Passet. Unlike the Sirius Passet Lagerstätte, fossil remains of non‐mineralized metazoans with limbs and other details of internal anatomy do not occur in the upper Buen Formation, although organic tubes assigned to a new selkirkiid stem group priapulid (Sullulika) are common. New taxa: Alutella siku sp. nov., Sullulika broenlundi gen. et sp. nov., Nevadotheca boerglumensis sp. nov., Kalaallitia myliuserichseni gen. et sp. nov., Nasaaraqia hyptiotheciformis gen. et sp. nov., Trapezovitus malinkyi sp. nov., Decoritheca? hageni sp. nov.
An agglutinated animal (or possibly protist) of the Late Proterozoic Clemente Formation biota cemented an array of tourmaline crystals (trigonal prisms; schorl/dravite composition) to its dorsal surface, presumably as ballast, in the earliest known case of an agglutinated animal. Quantitative confirmation of the spatial association (clustering) of the tiny crystals is demonstrated here by means of Kappa (K) value analysis. This discovery of this Proterozoic “crystal creature” reveals both the earliest known case of agglutination, the earliest known case of monomineralogic agglutination, and the earliest known bioaccumulation of tabular crystals of the same mineral. This case compares to the preferential selection of ilmenite to form an agglutinated exoskeleton in the Cambrian agmatan Volborthella. It also compares to the preferential selection of muscovite flakes to form the agglutinated Cambrian worm tube Onuphionella. Agglutinated dorsal skeletons of the Proterozoic and Early Cambrian utilized selected mineral types, including white mica, ilmenite, anatase, and tourmaline. All of these minerals potentially afford protection from UV-B radiation, and may have been deployed on the dorsal surfaces of these early animals to serve as sunscreen.
Many cladistic analyses of animal phylogeny have been published by authors arguing that their results are well supported. Comparison of these analyses indicates that there can be as yet no general consensus about the evolution of the animal phyla. We show that the various cladistic studies published to date differ significantly in methods of character selection, character coding, scoring and weighting, ground-pattern reconstructions, and taxa selection. These methodological differences are seldom made explicit, which hinders comparison of different studies and makes it impossible to assess a particular phylogeny outside its own scope. The effects of these methodological differences must be considered before we can hope to reach a morphological reference framework needed for effective comparison and combination with the evidence obtained from molecular and developmental genetic studies.
Singuuriqia simoni gen. et sp. nov. represents the first record of a priapulid worm from the Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) of North Greenland (Laurentia). It is defined by an unusually broad, longitudinally folded, foregut which tapers through the pharynx towards the anterior mouth; posteriorly, the same longitudinal folding is evident in the narrow gut. The slender, smooth, trunk in the unique specimen passes anteriorly into an oval proboscis which culminates in a smooth, extensible, pharynx with pharyngeal teeth. The capacity for substantial expansion of the foregut permitted rapid ingestion of food prior to digestion at leisure. Cololites suggest both carnivorous and deposit feeding behaviour, indicating that Singuuriqia, like the present day Priapulus, was probably omnivorous.
Despite many major advances in recent years, three key challenges remain in bringing clarity to the early history of the phylum: (1) identifying the origin, morphology and life modes of the first brachiopods; (2) understanding the relationships of the major groups to each other and higher sister taxa; and (3) unravelling the roles of the Cambrian and Ordovician radiations that set the agenda for much of subsequent brachiopod evolution. Since some 95% of all brachiopod taxa are extinct, the fossil record is the primary source of data to frame and test models for the evolution of the phylum. The acquisition of new, and the redescription of existing faunas, in precise spatial and temporal frameworks, using new and well-established analytical and investigative techniques, are as important as ever.
This review summarizes some major events in the evolution of body plans along the backbone of the arthropod tree, with a special focus on the origin of insects. The incompatibility among recent molecular phylogenies motivates a discussion about possible causes for failures: there is a worrisome lack of information in alignments, which can be visualized with spectra of split-supporting positions, and there are systematic errors occurring even when using correct models in maximum likelihood methods (Kück et al., this book). Currently, these problems cannot be avoided. Combining information from the fossil record and from extant arthropods, the morphology-based evolutionary scenario leads from worm-like stem-lineage arthropods via first euarthropods to the crown group of Mandibulata. The evolution of the mandibulate head is well documented in the Cambrian Orsten fossils. The evolution within crustaceans is also the evolution that leads to characters of the bauplan of myriapods and insects. It is argued that morphologicallymyriapods do not fit to the base of the mandibulatan tree and that this placement is also not plausible from a paleontological point of view. Available morphological evidencesuggests that myriapods are the sister-group to Hexapoda and that tracheates evolved from a marine ancestor that was similar in many ways to Remipedia. In the extant fauna, the Remipedia are the sister-group of Tracheata.
Arthropods are characterized by a rigid, articulating, exoskeleton operated by a lever-like system of segmentally arranged, antagonistic muscles. This skeletomuscular system evolved from an unsegmented body wall musculature acting on a hydrostatic skeleton, similar to that of the arthropods’ close relatives, the soft-bodied onychophorans. Unfortunately, fossil evidence documenting this transition is scarce. Exceptionally-preserved panarthropods from the Cambrian Lagerstätte of Sirius Passet, Greenland, including the soft-bodied stem-arthropod Pambdelurion whittingtoni and the hard-bodied arthropods Kiisortoqia soperi and Campanamuta mantonae, are unique in preserving extensive musculature. Here we show that Pambdelurion's myoanatomy conforms closely to that of extant onychophorans, with unsegmented dorsal, ventral and longitudinal muscle groups in the trunk, and extrinsic and intrinsic muscles controlling the legs. Pambdelurion also possesses oblique musculature, which has previously been interpreted as an arthropodan characteristic. However, this oblique musculature appears to be confined to the cephalic region and first few body segments, and does not represent a shift towards arthropodan myoanatomy. The Sirius Passet arthropods, Kiisortoqia and Campanamuta, also possess large longitudinal muscles in the trunk, although, unlike Pambdelurion, they are segmentally divided at the tergal boundaries. Thus, the transition towards an arthropodan myoanatomy from a lobopodian ancestor probably involved the division of the peripheral longitudinal muscle into segmented units.
Maikhanellids are a distinct group of Cambrian Fortunian small shelly fossils by the cap-shaped profiles and scaly shell ornamentation. According to the individual shell shape and ornamentation feature types of SO maikhanellids fossils which were collected from Xixiang botia, we confirmed the family Maikhanellidae content of six genera, which are Maikhanella, Ramenta, Purella, Ramentoides, Yunnannopleura and Mediata. Unlike the halkieriid animals whose shells and spicules are articulated on different body parts, maikhanellids were presumably yielded by siphogonuchitid spicules penetrating the intermediate matrix (the “spicule shell” hypothesis), and this is the reason that some researchers treated maikhanellids and co-occurring siphogonuchitids as synonyms. The affinities of Maikhanellids and siphogonuchitids remain debatable. Here, we report three dimensionally phosphatized maikhanellid shells and siphogonuchitid spicule bundles from the Cambrian Fortunian small shell faunas of South China. They differ from all the previously reported maikhanellids and siphogonuchitids, and may represent new types. The intact and smooth surface underneath the partially preserved scales of the shells challenges the “spicule-shell” hypothesis. The present siphogonuchitid spicules differ from the maikhanellid scales in size, morphology, and arrangement pattern, thus the spicules might not be derived from the shells. Whether the shells and spicule bundles were articulated on different body parts of the same animals remains unknown.
Three historical phases can be distinguished in the study of brachiopod systematics over the past 75 years. Prior to 1956, systematic neontologists and paleontologists struggled to reconcile differences in perceived evolutionary patterns (and thus classifications) based largely on static morphological differences observed separately among living brachiopods and among fossil brachiopods. Following 1956, patterns of morphological distribution began to be interpreted relative to the processes by which they were formed, and a more dynamic view of brachiopod phylogeny and classification resulted. Over the past decade, newer methodologies (phylogenetic systematics) have allowed older phylogenetic hypotheses to be tested and evaluated. The major challenges that brachiopod systematists now face are not unique to brachiopods; they concern improving the methods of phylogeny (and classification) reconstruction so that all the sources of data available to paleontologists can be utilized more effectively. In the future, I predict that more intensified, global fossil collecting, together with further investigation of the embryology and development of brachiopods, and molecular systematic research, will play an increasingly larger role in revising the classification currently in use.
Latest Precambrian through Early Cambrian tectonic history and stratigraphy are comparable in southeastern Cape Breton Island and the western Placentia-Bonavista axis, southeastern Newfoundland. The lithostratigraphic nomenclature of southeastern Newfoundland is used for this interval in Cape Breton Island and stratigraphic revisions are made. Twenty-six species are illustrated. Halkieria fordi n.sp. the conodont(?) "Rushtonites' asiatica n.sp., and the zhijinitid(?) Samsanoffoclavus matthewi n.gen. and sp. are described. Ischyrinia? sp. may be the oldest ischyrinoid rostroconch. -from Author
This paper attempts to summarize the literature on certain extant "Problematica' within or near the Metazoa. The groups reviewed represent taxa with only one or a few species that do or did significantly contribute to the discussion on the early radiation of the Metazoa or of the Bilateria. It is concluded that the problematic status of these taxa is due to poor knowledge of either their microanatomy or to incomplete understanding of their life-cycle. -from Authors
The astounding diversity of life that we see today is the product of species multiplication and morphological divergence through geological time. Evidence from the fossil record shows that this evolutionary radiation has not occurred at an even rate. Instead, relatively short-lasting phases of evolution have produced the major radiations that are seen in many taxonomic groups, such as flowering plants during the late Cretaceous. This volume surveys patterns of major evolutionary radiation and their possible causes.
The astounding diversity of life that we see today is the product of species multiplication and morphological divergence through geological time. Evidence from the fossil record shows that this evolutionary radiation has not occurred at an even rate. Instead, relatively short-lasting phases of evolution have produced the major radiations that are seen in many taxonomic groups, such as flowering plants during the late Cretaceous. This volume surveys patterns of major evolutionary radiation and their possible causes.
The German mining term lagerstatten, referring to a rock of any composition containing constituents of economic interest, has been widely applied to occurrences of abundant or unusually well preserved fossils (cf. Seilacher et al., 1985). The Middle Cambrian Burgess Shale of western Canada is perhaps the most famous of all fossil-lagerstatt, with many of the approximately 140 known species preserving exquisite details of the soft anatomy of members of a community of organisms that was fossilised more than 500 million years ago (Whittington, 1985: Conway Morris, 1979, 1986; Gould, 1989). Other well known examples include the Upper Cambrian 'Orsten' of southern Sweden, the Lower Devonian Hunsruck Slate and the Jurassic Solnhofen Limestone of Germany (Stürmer et al.. 1980; Muller, 1985; Barthel et al. 1990; summary in Briggs & Crowther, 1990, pp. 266–297). The term can be applied aptly to the Sirius Passet fauna of central North Greenland, where a wealth of exceptionally preserved fossils (e.g. Fig. 1) from tile Lower Cambrian Buen Formation has been recorded from a small locality in western Peary Land, near the south-western end of the broad valley known as Sirius Passet (Fig. 2). The locality yielding the Sirius
Three genera of sponges are described for the first time from the Lower Palaeozoic of North Greenland. ?Vauxia gracilenta Walcott, 1920 and Choia hindei (Dawson, 1896) are reported from the Buen Formation of Early Cambrian age; the specimens of the latter species are the largest known examples of Choia. A single specimen from the Chester Bjerg Formation of Late Silurian age is described as Diagoniella mica sp. nov., and is the smallest known species of the genus.
A new genus of nevadiid trilobite is described from the Lower Cambrian of Peary Land, central North Greenland, from the same horizon and locality from which a non-skeletised fauna has been recently reported. The new genus, BuenelIus, is tentatively assigned to the Nevadiidae Hupe, 1953, and comparisons are made with the genera Nevadia Walcott, 1910, Nevadella Raw, 1936, Callavia Matthew, 1897, Holmia Matthew, 1890 and Kjerulfia Kiaer, 1917.
The fifth and final field season in GGU's North Greenland programme (1978-80, 1984-85) comprised geological mapping and general geological investigations in the region between J. P. Koch Fjord (400 W) and Washington Land (65°W), the same area as the 1984 investigations. A working party of 40 participants, consisting of 12 geological two-man teams, a four-man drilling team and 12 supporting personnel, including aircraft crews, worked in the region for two months during the summer. The preliminary results of the geological work are presented in in this report.
This bulletin contains two papers describing aspects of the functional morphology and systematics of Early Palaeozoic untorted molluscs and bellerophontacean gastropods. A brief discussion of the potential role in early molluscan evolution of articulated halkieriids recently discovered from the Lower Cambrian of North Greenland forms an introduction to the volume.
Two Cambrian lepidote metazoans known from different respective types of preservation have been compared in order to elucidate their biology and affinities. The widely distributed Lower Cambrian Halkieria is represented by isolated hollow sclerites, probably of originally calcareous composition. The Middle Cambrian Wiwaxia is known from the Burgess Shale as isolated sclerites (scales and spines) and as more or less complete individuals. Although Halkieria sclerites were mineralized and those of Wiwaxia were probably not, there are fundamental structural and morphological similarities between the two. Both bad an imbricating scaly and spiny armour consisting of hollow sclerites with a longitudinally fibrous structure. The sclerites did not grow, but were probably moulted during the course of ontogenetic growth. Halkieria and Wiwaxia are regarded as closely related. Both are referred to the Order Sachitida He 1980. The sclerite armour of Halkieria is reconstructed on the template provided by Wiwaxia. The interpretation of sachitid sclerites as protective armour is an alternative to the interpretation by Jell (1981, Alcheringa 5)that sachitid sclerites were respiratory organs in an animal of probable annelid affinities. Sachitids are interpreted as sluggish, benthic deposit feeders that do not belong to any recognized phylum.
The vermiform pedicle is one of the most distinctive organs of modern lingulids, but it is rarely preserved. Only two fossil specimens of lingulids with pedicle casts have been reported, one from the Ordovician and the other from the Devonian. No record of fossil pedicles of Lingulella and Lingulepis , the dominant Cambrian and Early Ordovician lingulids, is known. Fossil lingulids from the Lower Cambrian of Chengjiang County, Yunnan, suggest that the structure and function of the pedicle of the lingulids has not changed significantly from its first appearance. A comparison of fossil pedicle of lingulids from the Lower Cambrian, Chengjiang County (China), the Burgess Shale, Middle Cambrian, British Columbia (Canada), the Trenton Formation, Middle Ordovician, New York (U.S.A.), and the Devonian, Devonshire (England, U.K.) shows that the delthyrial area to which the pedicle muscles are attached was reduced in length through time until these muscles were completely embraced by the two valves.
Two species, Lingulella chengjiangensis n. sp. and Lingulepis malongensis Rong, are described.
The enigmatic fossil Wiwaxia corrugata is organically preserved in the Burgess Shale (Middle Cambrian, British Columbia) and is therefore extractable by careful acid maceration of the mineralic matrix. High magnification transmitted light microscopy and SEM of macerated Wiwaxia sclerites reveal a substantial amount of previously undescribed structural and microstructural detail. Anatomical and histological comparison with modern organisms indicates that Wiwaxia sclerites are polychaete paleae (flattened setae) and that Wiwaxia was a jawed annelid broadly related to the extant polychaete families Chrysopetalidae and/or Aphroditidae (Palmyra). Canadia spinosa, an uncontested fossil polychaete from the same beds, shows a paleal microstructure identical to that of Wiwaxia. -from Author
Previous classifications of the major groups of cephalopods are based mainly on features of the shell and the siphuncle and are phenotypic. In a new approach, the classification is reinvestigated by means of cladistic analysis. The Cephalopoda are a monophyletic group of molluscs. Despite obvious differences between, for example, Nautilus and the Coleoidea, there are some unique synapomorphies that are exclusively shared by these two distinct evolutionary lines. The latest common ancestor of the cephalopods will be considered. In contrast to previous studies which have considered only the fossil record for a suitable candidate, the hypothetic ancestral cephalopod (HAC) is here reconstructed using characters of Recent taxa. A plausible scenario for the evolutionary steps leading to HAC will be presented. This includes a discussion of the position of the Cephalopoda within the Mollusca and their probable sister-group. -from Author
Annelid chaetae have long been valued by systematists for their diversity of form and intricate structural detail, especially in the class Polychaeta. In this group these epidermal products occur in the most widely varying form, ranging from the elongate, flexible spirals of the maldanid genus Nicomache (Kennedy and Kryvi 1978) to short, dentate uncini in sessile, tube-dwelling forms such as the spirorbids (Knight-Jones and Fordy 1979, Fig. 1B). Although most annelid chaetae are sculptured from a single piece, some polychaete chaetae are compound, composed of a distal article joined to an elongate, more proximal shaft by a relatively complex articulation (Fig. 1C). Fauchald’s (1977) key to the polychaete genera illustrates many chaetal types with simple line drawings. In contrast to their abundance and diversity among the polychaetes, chaetae are known to occur in only a single primitive genus of leeches (Acanthobdella); these characteristic structures are otherwise absent from these specialized annelids. Among the oligochaetes, chaetae are fewer and less diverse (Fig. 1 A) but also demonstrate a variety of taxonomically useful patterns (Brinkhurst 1982). Annelid chaetae have been discussed recently by Richards (1978) and Jamieson (1981).
Reference to fossil imprints of soft-bodied Ediacaran metazoans made by Hill and Bonney (1877, p. 757) recorded two of “those curious arrangements of concentric rings which have been supposed to be organisms” present on one of the bedding faces of the North Quarry, Woodhouse Eaves in Charnwood, Forest, Leicestershire, England (see Ford, 1958, 1963); the markings were dismissed as being “accidental ... (and) inorganic.” Early this century, P. Range and H. Schneiderhöhn collected fossil remains of equivalent age at Kuibis Farm in South West Africa (Namibia), and the organic nature of this material was confirmed by Gürich (1929, 1933). The history of discovery of such fossils during the mid part of the century (Sprigg, 1947, 1949; Ford, 1958, 1963, 1968, 1979a,b, 1981; Anderson and Misra, 1968) and the subsequent finding of similar materials widely sited about the globe are well known (e.g., Glaessner, 1984; Hofmann, 1987).
Four organ systems, pericardium of primitive molluscs, shell ontogeny and spicule formation in chitons and aplacophorans, chaetoderm oral shield, and aplacophoran radula, are described and their relationships discussed. The discussion suggests: 1) a coelomate ancestor of the molluscs; 2) a polyphyletic origin of shell, one for Conchifera and another for chitons; 3) a single class Aplacophora containing 2 taxa, the Chaetodermomorpha and Neomeniomorpha; 4) an archimolluscan radula with a pair of separate radular membranes bearing rows of single teeth. Evidence is presented that contradicts the following hypotheses: 1) an acoelomate origin of molluscs; 2) the division of aplacophorans into 2 classes; 3) the derivation of the univalved molluscan shell from a common stem with the 8-shelled chitons. The concept of a subphylum Aculifera is rejected as unnecessary since it holds no essential information. -Author
A study of the solute Dendrocystoides scoticus (Bather), from the Upper Ordovician Ashgill Series, near Girvan, Scotland produces much new anatomical information. The positions of head, tail, and tube feet in the feeding arm, hydropore, gonopore, gonad, pharynx, stomach, anus, brain, left trigeminal ganglion, gill slit (at posterior left in the head), notochord, and tail muscles are deduced. The work aimed at determining the phlogenetic, and therefore systematic position of the Soluta. -from Author
Transmission electron microscopic studies were carried out on the ventral pharyngeal organs in Ctenodrilus serratus and Scoloplos armiger. The pharyngeal organs are composed of a muscle bulbus and a tongue-like organ. In both species the muscle bulbus consists of transverse muscle fibres and interstitial cells with voluminous cell bodies and dorsoventral tonofilaments; the investing muscle runs into the tongue-like organ; the nuclei of the investing muscle fibres are located in caudal bulges; salivary glands are not present, but numerous gland cells occur in the bulbus epithelium. The tongue-like organ, however, is formed by lateral folds (C. serratus) or a bridge-like structure (S. armiger). The specific structure of the bulbus muscle is probably a homologous characteristic also occurring in several other polychaete families. The phylogenetic importance of this ventral pharynx is discussed and a hypothesis is suggested to explain the differentiation of certain other ventral pharyngeal organs from this probably primitive type.
Early Cambrian sections on the Yorke Peninsula have been systematically sampled. Their profuse biotas of sponges, algae, molluscs, trilobites, ostracodes, hyoliths, tommotiids, coeloscleritophorans, anabaritids, and a variety of other small skeletal fossils are described. New genera erected are Endoconchia (cyanobacterium), Taraxaculum (sponge), Microcoryne (possible octocoral), Eremactis, Hippopharangites (coeloscleritophorans), Kulparina (tommotiid), Stoibostrombus (ornamented cone), Archaeopetasus (smooth cone), Apistoconcha, Aroonia (brachiopod-like bivalved organisms), Parkula, Hyptiotheca (hyolithids), Triplicatella (uncertain affinity), Mackinnonia, Pararaconus (molluscs), Ardrossania (possible mollusc), Korobovia, Xela, Elicicola (trilobites), Epactridion (bradoriid), and Aetholicopalla (spherical, uncertain affinity). Trilobites from these and other sections in the same areas are used as the basis for a regional zonation of four zones. -from Authors
Molecular data suggest that the body plans of the major phyla for which the data exist originated independently of one another, although a well-defined branching sequence of living phyla is indicated by 18S rRNA phylogenetic trees. It is plausible, then, that the branching occurred much earlier in the history of the metazoa than has been suspected, virtually among acoelomate-grade forms during the Late Precambrian. If so, the locomotory adaptations associated with the rise of the body plans of living phyla must each be traced as an independent evolutionary invention, chiefly in the Early Cambrian.
