Adam Pritchard

Virginia Museum of Natural History

reptiles

Taylorsville Basin new site new finds

The femora of diapsids have undergone morphological changes related to shifts in postural and locomotor modes, such as the transition from plesiomorphic amniote and diapsid taxa to the apomorphic conditions related to a more erect posture within Archosauriformes. One remarkable clade of Triassic diapsids is the chameleon-like Drepanosauromorpha. Th...

Archosauromorph reptiles underwent rapid lineage diversification, increases in morphological and body size disparity, and expansion into new adaptive landscapes. Several of the primary early archosauromorph clades (e.g. rhynchosaurs) are easy to differentiate from others because of their characteristic body types, whereas the more lizard‐like and c...

Background Weigeltisauridae is a clade of small-bodied diapsids characterized by a horned cranial frill, slender trunk and limbs, and a patagium supported by elongated bony rods. Partial skeletons and fragments are definitively known only from upper Permian (Lopingian) rocks in England, Germany, Madagascar and Russia. Despite these discoveries, the...

Fossils of drepanosauromorphs, a clade of non-saurian diapsids, were once considered relatively rare in the Chinle Formation of the southwestern United States as well as in Upper Triassic rocks globally. Recent discoveries have shown that there are at least four drepanosauromorph taxa present in the Chinle Formation including Dolabrosaurus aquatili...

Teraterpeton hrynewichorum is an unusual archosauromorph reptile from the Upper Triassic (Carnian) Evangeline Member of the Wolfville Formation in Nova Scotia (Canada). Its long snout has transversely broad, cusped 'molariform' teeth posteriorly and lacks teeth anteriorly. The temporal region of the cranium is 'euryapsid' with large upper and close...

General anatomical comparisons between modern and fossil taxa have long been a source for functional and behavioral hypotheses in extinct lineages. For example, the forelimb morphology and hook-and-pull digging behavior of anteaters has been used as a model for the Triassic diapsid Drepanosaurus, which possesses a bizarre forelimb anatomy with asym...

Following the Permo-Triassic Extinction, large-bodied diapsid reptiles-with a body length >1 m-rapidly expanded their ecological roles. This diversification is reflected in enormous disparity in the development of the rostrum and adductor chamber. However, it is unclear how marked the diversity of the feeding apparatus was in contemporary small-bod...

The Triassic Period saw the first appearance of numerous amniote lineages (e.g. Lepidosauria, Archosauria, Mammalia) that defined Mesozoic ecosystems following the end Permian Mass Extinction, as well as the first major morphological diversification of crown-group reptiles. Unfortunately, much of our understanding of this event comes from the recor...

Supplemental Appendix A: A. Modifications to characters and codings from the matrix of Nesbitt et al. (2015).; Appendices for Main Text PDF (A–C)

Major transformations in brain size and proportions, such as the enlargement of the brain during the evolution of birds, are accompanied by profound modifications to the skull roof. However, the hypothesis of concerted evolution of shape between brain and skull roof over major phylogenetic transitions, and in particular of an ontogenetic relationsh...

The fossil record of early-diverging pan-archosaurs and pan-lepidosaurs in the Triassic is biased towards large-bodied animals (1+ meters). The Triassic Newark Supergroup of eastern North America has produced tantalizing specimens of small reptiles, hinting at high diversity on the continent. Among these is a remarkable diapsid skull (~2.5 cm lengt...

Estimating divergence times on phylogenies is critical in paleontological and neontological studies. Chronostratigraphically-constrained fossils are the only direct evidence of absolute timing of species divergence. Strict temporal calibration of fossil-only phylogenies provides minimum divergence estimates, and various methods have been proposed t...

Basal saurian lineages, especially archosauromorphs, diversified widely during the Triassic Period, exploring a remarkable range of different ecological roles (e.g., terrestrial predators, herbivores with complex teeth, aerial gliders). Many of these early lineages differ greatly from one another in the structure of the postcranium. Teraterpeton hr...

The tetrapod forelimb is one of the most versatile structures in vertebrate evolution, having been co-opted for an enormous array of functions. However, the structural relationships between the bones of the forelimb have remained largely unchanged throughout the 375 million year history of Tetrapoda, with a radius and ulna made up of elongate, para...

The avian skull is distinctive in its construction and in its function. Much of bird anatomical variety is expressed in the beak; but the beak itself, largely formed of the premaxillary bone, is set upon a shortened face and a bulbous, enlarged braincase. Here, we use original anatomical observations and reconstructions to describe the overall form...

During the Triassic, archosauromorphs became one of the first groups of diapsid reptiles to diversify in terms of body size and morphological disparity in both terrestrial and marine ecosystems across Pangaea. This seemingly rapid divergence, and the numerous unique body plans stemming from it, concomitantly has confounded reconstructions of archos...

Since the earliest Triassic, saurian reptiles have been critical components of terrestrial ecosystems. However, molecular and fossil evidence indicates that the divergence between the two constituent lineages (Lepidosauria, Archelosauria) took place deep in the Permian Period. A large number of early-diverging stem-archosaur and stem- lepidosaur cl...

We report on tanystropheids from the Late Triassic (middle Norian) Hayden Quarry of northern New Mexico (Chinle Formation, Hayden Quarry). These elements, consisting of isolated vertebrae and appendicular bones, represent the first unambiguously identified tanystropheid from western North America and likely the latest occurrence of the group, postd...

Eusuchian crocodyliforms, which include all living crocodylians, have historically been characterized by two anatomical specializations: a ball-in-socket vertebral joint and an extensive secondary hard palate with a pterygoid-bound internal choana. The Early Cretaceous neosuchian clade Susisuchidae is typically regarded as phylogenetically near Eus...

Drepanosaurs are an enigmatic clade of Late Triassic diapsids from Europe and North America with superficially chameleon-like bauplans. The phylogenetic position of the group among diapsids is contentious. Most hypotheses suggest that drepanosaurs are basal archosauromorphs closely related to 'protorosaurs' (e.g., Protorosaurus, Tanystropheus). Oth...

We describe three new fossil snakes on the basis of recently discovered vertebrae collected from the Upper Cretaceous (Maastrichtian) Maevarano Formation of Madagascar. One represents a new genus and species of madtsoiid, Adinophis fisaka, the third member of this family recognized from the Maevarano Formation. It exhibits dorsoventrally compressed...

Tanystropheids are a clade of long-necked archosauromorphs whose remains are largely restricted to marine deposits from the Triassic of Europe and Asia and almost entirely known from two-dimensionally crushed skeletons. Thus far, the occurrences of Tanytrachelos along the East Coast of the United States represent the westernmost confirmed record of...

The goniopholidid Eutretauranosuchus delfsi is currently known from two skulls from the Late Jurassic Morrison Formation of Colorado. Here we present a detailed osteology for a third Eutretauranosuchus delfsi specimen (AMNH FARB 570), consisting of a skull and fragmentary postcranium from Bone Cabin Quarry, Wyoming (Morrison Formation). Additional...

Drepanosauridae is a clade of putatively arboreal diapsids from the Late Triassic of Europe and North America. They are known primarily from crushed, two-dimensional skeletons discovered in Italy and eastern North America, though isolated occurrences are known from the United Kingdom and western United States. Here we report on a new drepanosaurid...

Goniopholidids are a group of Laurasian basal neosuchians that were common in the Juras- sic and Early Cretaceous. With long snouts and sprawling gaits, goniopholidids occupied a semiaquatic carnivorous niche currently allocated to crocodylians. Some species of Asian and North America goniopholidids possess a partially-incomplete secondary palate,...