Anatomical study of two previously undescribed specimens of Clevosaurus hudsoni (Lepidosauria: Rhynchocephalia) from Cromhall Quarry, UK, aided by computed tomography, yields additional information on the skeleton and hitherto undescribed bones

Rhynchocephalians were a successful, globally distributed group of diapsid reptiles that thrived in the Mesozoic. Multiple species of Clevosaurus existed worldwide in the Late Triassic and Early Jurassic, characterized by shearing bladelike teeth perhaps functionally analogous to the carnassial teeth of mammals. Morphometric analysis shows that the dentary morphospace of clevosaurs differs significantly from that of other rhynchocephalians. Five Clevosaurus species occupied islands in the Bristol Channel archipelago of the UK, but generally not those occupied by mammaliaforms, suggesting dietary character displacement. Identifying the diet of such ancient, small tetrapods has been difficult. To identify the nature of their feeding mechanics and ecology, we apply finite element analysis to two near complete three-dimensional skulls of the species Clevosaurus hudsoni and Clevosaurus cambrica to estimate bite force, resistance to bending and torsion and the distribution of stresses in the jaws during biting. Both species had bite forces and tooth pressures sufficient to break apart chitin indicating that, like early Mesozoic mammaliaforms, clevosaurs could feed on tough-shelled beetles and possibly small vertebrates. In addition, the mechanical advantage of the jaws falls within the range of early mammaliaforms, so though we cannot demonstrate niche partitioning between members of the two clades, it raises the prospect that they may have been functionally similar.

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“…We use digital 3D segmentation of the skulls of both taxa, as featured in O'Brien et al . (2018) and Chambi‐Trowell et al . (2019).…”

Section: Methodsmentioning

confidence: 97%

“…(AUP 11374; Fraser 1988); C. hudsoni X (NHMUK PV R36832; O'Brien et al . 2018; Chambi‐Trowell et al . 2019); C. wangi , C. mcgilli , C. petilus (Wu 1994; Jones 2006); two specimens of C. bairdi (NSM 988GF1.1 and reconstruction based on NSM 988GF1.1 + MCZ 9105; Sues et al .…”

Section: Methodsmentioning

confidence: 99%

Biomechanical properties of the jaws of two species of Clevosaurus and a reanalysis of rhynchocephalian dentary morphospace

et al. 2020

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“…Because of this pattern, tooth number and shape are the most common method for assessing maturity in rhynchocephalians (Fig. 3; Reynoso, 1996, 1997, 2003; Rieppel, 1992 c ; de Vivar Martínez & Soares, 2015; O'Brian, Whiteside & Marshall, 2018; Hsiou et al ., 2019). By contrast, there is only one use of teeth to assess maturity in squamates in our database: in the Cretaceous lizard Dicothodon bajaensis addition of teeth to the tooth row posteriorly, and ankylosis of the posteriormost tooth (Chavarría‐Arellano, Simões & Montellano‐Ballesteros, 2018).…”

Section: Methods Of Assessing Maturitymentioning

confidence: 99%

“…Maisano, 2001, 2002 a , b , c ; Bever et al ., 2015; Bever & Norell, 2017; Daza et al ., 2016; Frýdlová et al ., 2017), the scapula to the coracoid (e.g. Currie & Zhao, 1993; Brochu, 1995; Andres & Qiang, 2008; Bennett, 2014; O'Brian et al ., 2018), the carpals (e.g. Andres & Qiang, 2008) or tarsals (e.g.…”

Section: Methods Of Assessing Maturitymentioning

confidence: 99%

“…The most common single co‐ossification, or at least the most phylogenetically widespread, may be the fusion of the scapula and coracoid into a single element [used in e.g. Squamata (Dong, Wang & Evans, 2017); Rhynchocephalia (O'Brian et al ., 2018); Sauropterygia (Rothschild, Clark & Clark, 2018); Pantestudines (Bever et al ., 2015); Pseudosuchia (Walker, 1961; Brochu, 1995; Roberto‐da‐Silva et al ., 2020); Pterosauria (Hone et al ., 2012 b ); Dinosauria (Coombs & Maryańska, 1990; Currie & Zhao, 1993; Coria et al ., 2013; D'emic, 2013; Griffin, 2018; Navalón et al ., 2018)]. The fusion of these elements during ontogeny may represent the ancestral saurian condition (Griffin, 2018).…”

Section: Methods Of Assessing Maturitymentioning

confidence: 99%

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Assessing ontogenetic maturity in extinct saurian reptiles

et al. 2020

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Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.

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Hwiccewyrm trispiculum gen. et sp. nov., a new leptopleuronine procolophonid from the Late Triassic of southwest England

Butler,

Meade,

Cleary

et al. 2023

The Anatomical Record

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The fissure fill localities of southwest England and South Wales are well‐known for preserving rich assemblages of predominantly small‐bodied Late Triassic to Early Jurassic tetrapods, but many aspects of these assemblages remain contentious. The age of the Late Triassic fissures is disputed, with some lines of argument suggesting a latest Triassic (Rhaetian) age, whereas other evidence suggests they may be as old as Carnian. The fissures have been hypothesized by some workers to have formed on an archipelago, with island effects invoked to explain aspects of the assemblages such as the abundance of small‐bodied species. Procolophonids were a successful group of Triassic parareptiles, best known from Early to early Late Triassic assemblages, but have only recently been described from one of the fissure fill sites (Ruthin) based upon fragmentary remains. Here, we describe new procolophonid specimens from another fissure (Cromhall) that represent at least six individuals of different sizes, with much of the skeleton represented including well‐preserved skull material. The Cromhall procolophonid shows strong similarities to Late Triassic procolophonids from Scotland, Brazil and North America, but both autapomorphies and a unique character combination demonstrate that it represents a new species, which we name as Hwiccewyrm trispiculum gen. et sp. nov. Phylogenetic analysis places Hwiccewyrm in a derived clade within Leptopleuroninae, together with Leptopleuron, Hypsognathus, and Soturnia. The largest specimens of Hwiccewyrm demonstrate a body size that is similar to Leptopleuron and Hypsognathus, supporting other recent work that has questioned the insular dwarfism hypothesis for the fissure fill assemblages.

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Anatomical study of two previously undescribed specimens of Clevosaurus hudsoni (Lepidosauria: Rhynchocephalia) from Cromhall Quarry, UK, aided by computed tomography, yields additional information on the skeleton and hitherto undescribed bones

Cited by 19 publications

References 28 publications

Biomechanical properties of the jaws of two species of Clevosaurus and a reanalysis of rhynchocephalian dentary morphospace

Biomechanical properties of the jaws of two species of Clevosaurus and a reanalysis of rhynchocephalian dentary morphospace

Assessing ontogenetic maturity in extinct saurian reptiles

Hwiccewyrm trispiculum gen. et sp. nov., a new leptopleuronine procolophonid from the Late Triassic of southwest England

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