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

Abstract

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.

An exceptionally preserved Sphenodon-like sphenodontian reveals deep time conservation of the tuatara skeleton and ontogeny

“…Some of these results, especially the distinct region of the morphospace occupied by clevosaurids, are similar to a previous analysis focusing on mandibular disparity data 52 , with the difference of our sampled South American taxon ( C. brasiliensis herein) being closer to European taxa than to the North American taxon ( C. bairdi ) (Fig. 9 ).…”

“…An important limitation of the morphospace result is the poor fossil record of sphenodontians from the Cretaceous onwards—reflected here and in all available assessments of sphenodontian morphospace 20 , 50 , 52 . It is possible that this poor fossil record is a representation of true low taxonomic diversity and not simply a collection bias, at least in the northern hemisphere where collection efforts have historically been more intense than in southern continents 65 .…”

“…Previous analyses of sphenodontian morphological disparity and morphospace occupation were based on 2D morphometric characters obtained from the mandibles 50 , 52 or from drawings of reconstructed fossil skulls 20 . Despite the necessary reduction in the number of characters used for assessing the morphospace of sphenodontians herein to avoid spurious results driven by large amounts of missing data, the final number of variables and taxon sampling assessed herein are similar in scale to those previous studies.…”

Integrated phylogenomic and fossil evidence of stick and leaf insects (Phasmatodea) reveal a Permian–Triassic co-origination with insectivores

“…Mammaliaforms diversified in the Late Triassic and Early Jurassic, as indicated by molecular clock analyses and fossil evidence [ 40 , 84 – 86 ]. Dentition and jaw morphology suggest that these mammaliaforms and early mammals depended on a predominantly insect-based diet [ 39 , 87 – 91 ]. The earliest diverging pterosaur clade, the Late Triassic Eopterosauria, were insectivorous as suggested by dental evidence, and further insectivorous pterosaurs are known from the Jurassic to the Early Cretaceous [ 92 , 93 ].…”

From fibre to function: are we accurately representing muscle architecture and performance?

“…A popular approach, particularly in biomechanical evaluations of skull mechanics in extinct taxa, has been to reconstruct all muscles as parallel fibred with fibre lengths equal to the total length of the MTU at a specific length or joint posture (Button, Barrett & Rayfield, 2016; Gignac & Erickson, 2017; Adams et al ., 2019; Chambi‐Trowell et al ., 2020), and subsequently use these values in the calculation of PCSA (Fig. 1A).…”