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A redescription of the early archosauromorph Protorosaurus speneri MEYER, 1832, and its phylogenetic relationships
Abstract
Having been described in 1710, the first specimen of Protorosaurus speneri is one of the first fossil reptiles ever described. The only major monograph of the species was published in 1856, based on the 25 specimens available at that time. However, the skull anatomy remained almost unknown. Although the monograph on Protorosaurus contains very detailed descriptions, many anatomical features of the postcranium remained unclear due to extreme crushing of most specimens. Recently discovered material, especially a complete skull, the first juvenile, and a less crushed almost complete skeleton, provided the incentive to revise the anatomy of Protorosaurus. The new material allows a reconstruction of the skull for the first time as well as that of several postcranial elements, e.g. a complete interclavicle and a complete pubis. Furthermore, several anatomical features e.g. the well developed humerus and the number and arrangement of tarsal elements, can be described in more detail. The first juvenile specimen of Protorosaurus provides new insights into the ontogeny of the pelvic region and the tarsal elements. Protorosaurus is a member of the archosauromorph group Prolacertiformes, a group generally considered to be monophyletic. The anatomy of Protorosaurus will therefore be compared to that of other well known representatives of the group. The comparison shows that the skull anatomy of Protorosaurus closely resembles that of Prolacerta broomi, Macrocnetnus bassanii, and Pamelaria dolichotrachela. The postcranium is similar to that of Prolacerta broomi and Pamelaria dolichotrachela. Because the phylogenetic status and make-up of the Prolacertiformes is currently discussed controversially, a preliminary computer-aided, cladistic analysis is performed based on the dataset of the first author postulating a paraphyletic Prolacertiformes. Over 30% of the original codings were corrected for Protorosaurus, and the analysis was also modified with regard to the included taxa. The new analysis includes 17 taxa and 144 characters. Protorosaurus turns out to be a basal archosauromorph and the direct sister taxon of Megalancosaurus. The Prolacertiformes themselves are paraphyletic with Prolacerta and Pamelaria being more closely related to the Archosauriformes. The anatomical similarities between Protorosaurus, Prolacerta and Pamelaria must hence be interpreted as convergent. If Megalancosaurus is deleted from the analysis, Protorosaurus falls into an unresolved trichotomy with (Tanystropheus plus Macrocnemus), which becomes the direct sister taxon to the monophylum consisting of (Pamerlaria plus Prolacerta plus (Euparkeria plus Proterosuchus)). Furthermore, in this case the Choristodera fall outside the Sauria.
... ancestral condition of Archosauromorpha. Although Protorosaurus speneri possessed seven cervical and 18 or 19 dorsal vertebrae (A.R., personal observation) [23,51,52], some authors have hypothesized that the ancestral state for vertebral counts in Archosauromorpha included a significantly higher number of presacral vertebrae-around 31 [23]. This reconstruction is highly unlikely, especially in the light of new studies on the phylogeny of the group [15,50]. ...
The Triassic radiation of vertebrates saw the emergence of the modern vertebrate groups, as well as numerous extinct animals exhibiting conspicuous, unique anatomical characteristics. Among these, members of Tanystropheidae (Reptilia: Archosauromorpha) displayed cervical vertebral elongation to an extent unparalleled in any other vertebrate. Tanystropheids were exceptionally ecologically diverse and had a wide spatial and temporal distribution. This may have been related to their neck anatomy, yet its evolution and functional properties remain poorly understood. We used geometric morphometrics to capture the intraspecific variation between the vertebrae comprising the cervical column among early archosauromorphs, to trace the evolutionary history of neck elongation in these animals. Our results show that the cervical series of these reptiles can be divided into modules corresponding to those of extant animals. Tanystropheids achieved neck elongation through somite elongation and a shift between cervical and thoracic regions, without presacral vertebrae count increase—contrary to crown archosaurs. This suggests a peculiar developmental constraint that strongly affected the evolution of tanystropheids. The data obtained just at the base of the archosauromorph phylogenetic tree are crucial for further studies on the modularity of vertebral columns of not only Triassic reptile groups but extant and other extinct animals as well.
... The parietal table is narrow, but flares posteriorly into the parietal 'wings' marking the posterior borders of the sub-circular supratemporal fenestrae. These parietal 'wings' are oriented posterolaterally as in most early archosauromorphs, except Tanystropheus spp., Protorosaurus speneri and Azendohsaurus madagaskarensis, which exhibit a lateral orientation of these processes (Gottmann-Quesada & Sander 2009;Flynn et al. 2010;Spiekman et al. 2020a). The prominent pineal foramen is of an elongate oval shape. ...
The non-archosauriform archosauromorph Dinocephalosaurus orientalis was first described from the Upper Member of the Guanling Formation (late Anisian, Middle Triassic) of Guizhou Province by Li in 2003 on the basis of a complete articulated skull and the first three cervical vertebrae exposed in dorsal to right lateral view. Since then, additional specimens have been discovered in southwestern China. Here, five newly discovered specimens are described for the first time, and redescriptions of the holotype IVPP V13767 and another referred specimen, IVPP V13898, are provided. Together, these permit the description of the complete skeleton of this remarkable long-necked marine reptile. The postcranial skeleton is as much as 6 metres long, and characterised by its long tail and even longer neck. The appendicular skeleton exhibits a high degree of skeletal paedomorphosis recalling that of many sauropterygians, but the skull and neck are completely inconsistent with sauropterygian affinities. The palate does not extend back over the basisphenoid region and lacks any development of the closed condition typical of sauropterygians. The arrangement of cranial elements, including the presence of narial fossae, is very similar to that seen in another long-necked archosauromorph, Tanystropheus hydroides, which at least in part represents a convergence related to an aquatic piscivorous lifestyle. The long and low cervical vertebrae support exceptionally elongate cervical ribs that extend across multiple intervertebral joints and contribute to a ‘stiffening bundle of ribs’ extending along the entire ventral side of the neck, as in many other non-crocopodan archosauromorphs. The functional significance of the extraordinarily elongate neck is hard to discern but it presumably played a key role in feeding, and it is probably analogous to the elongate necks seen in pelagic, long-necked plesiosaurs. Dinocephalosaurus orientalis was almost certainly a fully marine reptile and even gave birth at sea.
... Indeed, in most nonsaurian diapsids (e.g. Claudiosaurus, Youngina; [26,27]), and early saurians (Clevosaurus, Protorosaurus, Prolacerta; [28][29][30]), the premaxilla is restricted to the anterior extremity of the rostrum, with the external naris located very anteriorly on the skull, and the nasal is platelike, forming a significant portion of the lateral surface of the rostrum. Weigeltisaurids also share this general morphology, although they show a short premaxillary rostrum [4]. ...
Wapitisaurus problematicus was initially described as a member of the Weigeltisauridae, a clade of Late Permian gliding reptiles from Eurasia and Madagascar. However, the poor preservation of the holotype and only known specimen, from the lower Sulphur Mountain Formation at Ganoid Ridge (British Columbia, Canada), raised doubts about this assignment. Here, we redescribe W. problematicus and reassess its systematic position among diapsid reptiles. Comparison with all known weigeltisaurids, as well as contemporaneous reptiles from the Sulphur Mountain Formation, indicates that the taxon instead represents a thalattosauroid thalattosauriform, with noted similarities to Thalattosaurus and Paralonectes. This reidentification restricts weigeltisaurids to the Late Permian, with no occurrence in North America. Wapitisaurus problematicus potentially represents one of the oldest thalattosauriforms and increases our understanding of their diversity and disparity during the late Early and Middle Triassic. The close morphological similarities with later (thalattosauroid) thalattosauriforms and their high abundance in (shallow) marine settings may indicate an earlier invasion of this realm than previously assumed. This parallels observations in early ichthyopterygians with widespread opportunistic trophic niche diversification occurring relatively rapidly after the end-Permian mass extinction event.
... Using the following references, all taxa were coded for these characters, as well as the necessary recodings of the reworked states of characters 69 and 70: Ammorhynchus navajoi [89], Bentonyx sidensis [66,91], Brasinorhynchus mariantensis [12], Eohyosaurus wolvaardt [11], Fodonyx spenceri [65,66], Howesia browni [90], Hyperodapedon gordoni [20], 'Hyperodapedon' huenei [7], 'Hyperodapedon' tikiensis [10], Isalorhynchus genovefae [9], Langeronyx brodiei [17,65], Macrocephalosaurus mariensis [13,93], Mesodapedon kuttyi [10,77], Mesosuchus browni), Oryctorhynchus bairdi [18], Paradapedon huxleyi [6], Prolacerta browni [94,95], Protorosaurus speneri [96], Rhynchosaurus articeps [65], 'Scaphonyx' sanjuanensis [93,97], Stenaulorhynchus stockleyi [86,93], Supradapedon stockleyi [13], Teyumbaita sulcognathus [67], and the "Zimbabwe form" [68,93]. ...
New discoveries in the lower Popo Agie Formation (lower carbonate unit) of central Wyoming necessitated a reevaluation of USNM 494329 from the same unit, the only known hyperodapedontine rhynchosaur in western North America. Well known from Gondwanan deposits, hyperodapedontines appear to be restricted to the Carnian age (Late Triassic), with the exception of Teyumbaita in the earliest Norian age (Late Triassic) of Brazil. Initially assigned to c.f. ‘Hyperodapedon’ sanjuanensis, our phylogenetic analyses reject this hypothesis, in support of a sister relationship between USNM 494329 (Beesiiwo cooowuse, gen. et. sp. nov.) and Oryctorhynchus bairdi forming an early-diverging clade that is only distantly related to ‘H.’ sanjuanensis. Five additional specimens recovered from the lower Popo Agie are described. Three are referred to B. cooowuse, and another two are placed closer to Hyperodapedon and the remainder of Hyperodapedontinae. Our analysis demonstrates potential temporal distinction between a grade of earliest-diverging hyperodapedontines (including all Wyoming taxa) and a exclusively Late Carnian, Southern Pangaean hyperodapedontine clade (including ‘H.’ sanjuanensis). We consider the lower Popo Agie Formation to represent the first nonmarine Late Triassic unit of Western North America that can be confidently restricted to the Carnian age.
The anatomy of Late Triassic drepanosauromorphs is re-examined, with a focus on the previously published surface models of the holotype of Avicranium renestoi from the Norian of North America. We comment on the cranial anatomy of this taxon and propose a new reconstruction of the skull and mandible. Contrary to previous interpretations, the entire rostrum and most of the palate are not preserved in this specimen. We also suggest that some proposed plesiomorphic characters may result from incomplete ossification due to immaturity. These new observations are compiled into a new morphological phylogenetic dataset designed to address the monophyly of ‘Avicephala’, the group comprising the Late Permian gliding reptiles Weigeltisauridae, and the Late Triassic chameleon-like Drepanosauromorpha. We recover Weigeltisauridae as stem-saurian diapsids and Drepanosauromorpha as sister-group to Trilophosauridae among archosauromorphs, thus implying the paraphyly of ‘Avicephala’. Drepanosauromorphs and trilophosaurids are recovered as sister-taxa for the first time, as supported by several cranial and postcranial synapomorphies. This new phylogenetic position of Drepanosauromorpha reduces the group’s ghost lineage that now does not necessarily cross the Permian–Triassic boundary. However, much remains unknown of the early history of trilophosaurids and drepanosauromorphs, and of the evolution of arboreality in Triassic archosauromorph reptiles.
Some of the earliest members of the archosaur-lineage (i.e., non-archosauriform archosauromorphs) are characterised by an extremely elongated neck. Recent fossil discoveries from the Guanling Formation (Middle Triassic) of southern China have revealed a dramatic increase in the known ecomorphological diversity of these extremely long-necked archosauromorphs, including the fully marine and viviparous Dinocephalosaurus orientalis. These recent discoveries merit a reinvestigation of enigmatic Triassic diapsid fossils from contemporaneous European deposits housed in historical collections. Here, we provide a redescription of Trachelosaurus fischeri, represented by a single, disarticulated specimen first described in 1918. Due to its unique morphology, which includes short, bifurcating cervical ribs, and a high presacral vertebral count, this taxon has been referred to either as a “protorosaurian” archosauromorph or a sauropterygian. Our revision clearly shows that Trachelosaurus represents the first unambiguous Dinocephalosaurus- like archosauromorph known from outside the Guanling Formation. Our finding has important systematic implications. Trachelosauridae Abel, 1919 represents the senior synonym for the recently identified Dinocephalosauridae Spiekman, Fraser and Scheyer, 2021. Based on our phylogenetic analyses, which employ two extensive datasets, we also corroborate previous findings that tanystropheids and trachelosaurids represent two families within a larger monophyletic group among non-crocopodan archosauromorphs, which is here named Tanysauria (clade nov.). Trachelosauridae is minimally composed of Trachelosaurus fischeri, Dinocephalosaurus orientalis, Pectodens zhenyuensis, and Austronaga minuta, but one of our analyses also found a probably taxonomically broader clade that may also include Gracilicollum latens and Fuyuansaurus acutirostris. Trachelosaurus fischeri considerably expands the known spatial and temporal range of Trachelosauridae to the earliest Anisian and the Central European Basin. Our findings add to the growing evidence for the presence of a diverse group of fully marine reptiles during the Middle Triassic
Summary: The Panchet Formation of northeastern India preserves an association of dwarf vertebrates (Early Triassic) with a single valid archosauromorph species, the protesosuchid Samsarasuchus pamelae. Two other species of archosauromorphs have been named for this unit: "Ankistrodon indicus" and "Teratosaurus(?) bengalensis." "Ankistrodon indicus", based on a fragment of maxilla with two partial teeth, is indistinguishable from other species of protesosuchids and is considered a nomen dubium. "Teratosaurus(?) bengalensis" is represented by an almost complete isolated tooth that was differentiated from "Ankistrodon indicus" by the presence of mesial denticles. "Teratosaurus(?) Bengalensis" is also indistinguishable from other valid species of protesouchids and is probably considered to be a nomen dubium. However, it remains unresolved whether "Teratosaurus(?) bengalensis" represents a second species of Panchet archosauromorph distinct from Samsarasuchus pamelae and "Ankistrodon indicus" because the presence of mesial denticles cannot be determined in these species due to their incompleteness. Here we describe two new specimens of Panchet's Proterosuchidae collected at the same locality as the holotypes of the three species mentioned above. These new specimens are maxilla fragments and one of them has almost complete teeth with mesial denticles in the apical portion of the crowns, as in "Teratosaurus(?) bengalensis." The rest of its morphology is congruent with that of Samsarasuchus pamelae and "Ankistrodon indicus". The specimens reported here expand our anatomical knowledge of the Panchet Arcosauriform Association and indicate that there is currently no evidence of the presence of more than one valid species of Arcosauromorph in the Panchet Formation.
Among numerous marine reptiles discovered in the Triassic eastern Tethys, today's Southern China, Dinocephalosaurus is a bizarre animal comparable to European Tanystropheus in developing a prominently long neck. These two taxa are respectively assigned to Dinocephalosauridae and Tanystropheidae, and the two families and other basal members collectively form an early-diverging clade of Archosauromorpha. Here we report a new archosauromorph specimen, IVPP V18579, excavated from the lower Middle Triassic (Anisian), from Luoping, Yunnan in southwestern China. Compared with all the hitherto known dinocephalosaurids and tanystropheids, this skeletally mature individual is exclusively similar to Dinocephalosaurus in a number of characteristics, particularly with the long posterodorsal process of the premaxilla extending posteriorly beyond the level of the external nares, the concave posterior margin of the anteroposteriorly broad quadrate, and the strongly expanded distal end of the chevron in most of the caudal vertebrae. However, this reptile is much smaller than Dinocephalosaurus and different from Dinocephalosaurus and the other dinocephalosaurid, Pectodens, in many aspects, such as an anteriorly tapering long rostrum, the dentition composed of short conical teeth with less heterodonty, relatively but obviously tall neural spines of the axis and the anterior cervical vertebrae. Our phylogenetic analysis suggests that the new archosauromorph is a dinocephalosaurid, and then we erect Austronaga minuta gen. et sp. nov. based on this specimen. Detailed comparisons in osteological anatomy and the discussion about its potential aquatic adaptation of this new taxon are also provided.
Proterosuchidae represents the oldest substantial diversification of Archosauromorpha and plays a key role in understanding the biotic recovery after the end-Permian mass extinction. Proterosuchidae was long treated as a wastebasket taxon, but recent revisions have reduced its taxonomic content to five valid species from the latest Permian of Russia and the earliest Triassic (Induan) of South Africa and China. In addition to these occurrences, several isolated proterosuchid bones have been reported from the Induan Panchet Formation of India for over 150 years. Following the re-study of historical specimens and newly collected material from this unit, we erect the new proterosuchid species Samsarasuchus pamelae , which is represented by most of the presacral vertebral column. We also describe cf. proterosuchid and proterosuchid cranial, girdle and limb bones that are not referred to Samsarasuchus pamelae . Phylogenetic analyses recovered Samsarasuchus pamelae within the new proterosuchid clade Chasmatosuchinae. The taxonomic diversity of Proterosuchidae is substantially expanded here, with at least 11 nominal species and several currently unnamed specimens, and a biogeographical range encompassing present-day South Africa, China, Russia, India, Brazil, Uruguay and Australia. This indicates a broader taxonomic, phylogenetic and biogeographic diversification of Proterosuchidae than previously thought in the aftermath of the end-Permian mass extinction.
Most living reptile diversity is concentrated in Squamata (lizards, including snakes), which have poorly known origins in space and time. Recently, †Cryptovaranoides microlanius from the Late Triassic of the United Kingdom was described as the oldest crown squamate. If true, this result would push back the origin of all major lizard clades by 30–65 Myr and suggest that divergence times for reptile clades estimated using genomic and morphological data are grossly inaccurate. Here, we use computed tomography scans and expanded phylogenetic datasets to re-evaluate the phylogenetic affinities of †Cryptovaranoides and other putative early squamates. We robustly reject the crown squamate affinities of †Cryptovaranoides, and instead resolve †Cryptovaranoides as a potential member of the bird and crocodylian total clade, Archosauromorpha. Bayesian total evidence dating supports a Jurassic origin of crown squamates, not Triassic as recently suggested. We highlight how features traditionally linked to lepidosaurs are in fact widespread across Triassic reptiles. Our study reaffirms the importance of critically choosing and constructing morphological datasets and appropriate taxon sampling to test the phylogenetic affinities of problematic fossils and calibrate the Tree of Life.
A juvenile Macrocnemus bassanii from Besano shows remains of scale covering in the sacral and proximal caudal region. The scales are preserved as fossilized elements and not as impressions. By comparison with another specimen of Macrocnemus, a taphonomic model is proposed to explain the pattern of preservation; suggesting that rapid burial in marine sediment occurred just after death, and that the well developed musculature of the sacral and proximal caudal regions contributed to the process of phosphatization of the scales, allowing their fossilization.
Boreopricea funerea from the Lower Triassic of northern Russia is a prolacertiform diapsid, superficially similar to Prolacerta from the Lower Triassic of South Africa. The skull is damaged, but relatively complete. The lower temporal bar is absent. Some parts of the skeleton of Boreopricea, in particular some of the vertebrae and the foot, are well preserved, and offer clear evidence of prolacertiform affinities. Nineteen species of prolacertiform have been described. Their affinities are difficult to resolve because available specimens for many of the taxa are incomplete. A series of cladistic analyses shows the existence of a tanystropheid clade (Tanystropheus, Tanvtrachelos), to which are allied Cosesaurus, Malerisaurus, Boreopricea, and Macrocnemus as successive outgroups. A new synapomorphy of prolacertiforms may be the tight association of astragalus, calcaneum, centrale, and distal tarsal 4 in the ankle, with the centrale in contact with the tibia.
The first prolacertiform from the British Isles is described. The type specimen of Rhombopholis scutulata, from the Middle Triassic of Warwick, was originally described as a temnospondyl amphibian. The specimen contains bones belonging to a large and a small prolacertiform, both possibly of the same species, as well as scales of a palaeonisciform fish. Prolacertiform characters of the small individual include long and low cervical vertebral neural spines, horizontal neural spine tables on the cervical vertebrae, tall rectangular dorsal vertebral neural spines, and, in a specimen of the presumed larger individual, a strong preacetabular crest on the ilium. Other material of the prolacertiform is noted from Warwick and Bromsgrove. The material is inadequate for confident diagnosis, but it shows closest similarities with Macrocnemus from the Middle Triassic of continental Europe.