Sterling J. Nesbitt

Virginia Tech

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Co-Authors

Michelle R. Stocker

Virginia Tech

Randall B. Irmis

Natural History Museum of Utah

Alan H. Turner

Stony Brook University

Richard J. Butler

University of Birmingham

William G. Parker

Petrified Forest National Park

Kenneth D. Angielczyk

Field Museum of Natural History

Roger M. H. Smith

California Institute of Technology

Christian A. Sidor

Burke Museum of Natural History and Culture

Nathan D. Smith

Natural History Museum of Los Angeles County

Adam D. Marsh

Petrified Forest National Park

Cooperative Institutions

John Wiley & Sons (United States)

Hudson Institute

Liechtenstein Institute

University of Utah

Williams (United States)

American Museum of Natural History

Virginia Tech

Stony Brook University

University of California, Berkeley

Field Museum of Natural History

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Papers

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Anatomy and phylogenetic affinities of a new silesaurid assemblage from the Carnian beds of south Brazil

Figshare (2023)

Gabriel Mestriner Júlio C. A. Marsola Sterling J. Nesbitt Átila Augusto Stock Da‐Rosa Max C. Langer

New specimens and the reassessment of many silesaurids have recently shed light on the origin and early evolution of dinosaurs and their close relatives. Yet, the group is relatively poorly represented in South America, an area that likely played an important role in dinosaurian origins. Since the discovery of Sacisaurus agudoensis from the Norian Caturrita Formation, only the fragmentary Gamatavus antiquus and Amanasaurus nesbitti have been reported from the Triassic of south Brazil. Here we describe disarticulated silesaurid remains from Waldsanga, one of the most important tetrapod-bearing localities of the Santa Maria Formation, which represent the second Carnian occurrence of the group in Brazil. The postcranial elements exhibit a combination of dinosauromorph symplesiomorphies and silesaurid diagnostic traits, showing that a conservative anatomy is pervasive among early dinosauromorphs. We also conducted a set of exploratory analyses to infer the phylogenetic relations of the new occurrence and the robustness of some of the most recent phylogenetic hypotheses in face of the increasing diversity of Silesauridae. This revealed a rather uncertain evolutionary scenario not only for Silesauridae, but for early dinosauromorphs in general.

Affinities

Assemblage (archaeology)

10.6084/m9.figshare.24015105

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Theropod Tree from The evolution and role of the hyposphene-hypantrum articulation in Archosauria: phylogeny, size and/or mechanics?

Figshare (2019)

Candice M. Stefanic Sterling J. Nesbitt

Nexus File for Character State Mapping in Theropods

Articulation (sociology)

Tree (set theory)

10.6084/m9.figshare.9852971

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The osteology of Shuvosaurus inexpectatus, a shuvosaurid pseudosuchian from the Upper Triassic Post Quarry, Dockum Group of Texas, USA

The Anatomical Record (2024)

Sterling J. Nesbitt Sankar Chatterjee

Abstract A vast array of pseudosuchian body plans evolved during the diversification of the group in the Triassic Period, but few can compare to the toothless, long‐necked, and bipedal shuvosaurids. Members of this clade possess theropod‐like character states mapped on top of more plesiomorphic pseudosuchian character states, complicating our understanding of the evolutionary history of the skeleton. One taxon in this clade, Shuvosaurus inexpectatus has been assigned to various theropod dinosaur groups based on a partial skull and referred material and its postcranium was assigned to a different taxon in Pseudosuchia. After the discovery of a skeleton of a shuvosaurid with a Shuvosaurus ‐like skull and a pseudosuchian postcranial skeleton, it became clear Shuvosaurus inexpectatus was a pseudosuchian. Nevertheless, a number of questions have arisen about what skeletal elements belonged to Shuvosaurus inexpectatus , the identification of skull bones, and the resulting implication for pseudosuchian evolution. Here, we detail the anatomy of the skeleton Shuvosaurus inexpectatus through a critical lens, parse out the bones that belong to the taxon or those that clearly do not or may not belong to the taxon, rediagnose the taxon based on these revisions, and compare the taxon to other archosaurs. We find that Shuvosaurus inexpectatus possesses similar anatomy to other shuvosaurids but parts of the skeleton of the taxon clarifies the anatomy of the group given that they are preserved in Shuvosaurus inexpectatus but not in others. Shuvosaurus inexpectatus is represented by at least 14 individuals from the West Texas Post Quarry (Adamanian holochronozone) and all Shuvosaurus inexpectatus skeletal material from the locality pertains to skeletally immature individuals. All of the skeletons are missing most of the neural arches, ribs, and most of the forelimb. We only recognize Shuvosaurus inexpectatus from the Post Quarry and all other material assigned to the taxon previously is better assigned to the broader group Shuvosauridae.

Postcrania

Osteology

Skeleton (computer programming)

10.1002/ar.25376

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The Osteology and Phylogenetic Position of Luperosuchus fractus (Archosauria: Loricata) from the Latest Middle Triassic or Earliest Late Triassic of Argentina

Ameghiniana (2017)

Sterling J. Nesbitt Julia B. Desojo

Large archosaurs from the early part of the archosaur radiation are exceedingly rare and with few exceptions, most of these remains consist of fragmentary postcrania. We redescribe the fragmentary skull of Luperosuchus fractus from the early Middle—Late Triassic Chañares Formation of Argentina, assign newly discovered fragments from the original excavation to the same individual, and analyze its phylogenetic affinities. The dorsally convex and mediolaterally compressed anterior portion of the nasal (= 'Roman-nose'), convex and circular knob on the dorsolateral margin of the postorbital, and a long anterior process of the prefrontal that fails to extend to the anterior end of the frontal are considered autapomorphies of Luperosuchus. The elongated gap between the nasal and maxilla is likely an artifact of preservation and this prompted a critical reevaluation of the supposed openings in the anterior portion of the skull of other suchians. We confirm that Luperosuchus is a loricatan (composed mostly of the taxa classically termed as 'rauisuchians') using a well sampled phylogeny and find a close relationship with the other large southwestern Pangean forms, Prestosuchus chiniquensis and Saurosuchus galilei. We also show that the holotype of Luperosuchus is the only known specimen of the taxon and all other previously referred material cannot be assigned with confidence to it.

Autapomorphy

Osteology

10.5710/amgh.09.04.2017.3059

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Citations (25)

A Detailed description of Rugarhynchos sixmilensis, gen. et comb. nov. (Archosauriformes, Proterochampsia), and cranial convergence in snout elongation across stem and crown archosaurs

Figshare (2020)

Brenen M. Wynd Sterling J. Nesbitt Michelle R. Stocker Andrew B. Heckert

The Triassic Period (252–201.5 Ma) records a great expansion of saurian diversity and disparity, particularly in skull morphology. Stem archosaurs exhibit substantial cranial disparity, especially by taxa either shortening or elongating the skull. This disparity is exemplified in the North American Late Triassic proterochampsians by the ‘short-faced’ Vancleavea and the ‘long-faced’ doswelliids. To critically investigate skull elongation and character evolution in these proterochampsians, we evaluate ‘Doswellia’ sixmilensis, known from much of a skull, cervical centra, and osteoderms from the Bluewater Creek Member of the Chinle Formation of New Mexico. We redescribe the holotype based on extensive repreparation of the holotype material, resulting in the identification of the orbit and clarifying the extent of related bones. As such, the diagnosis of the taxon is substantially modified and a new genus, Rugarhynchos, gen. nov., is erected. Rugarhynchos sixmilensis, gen. et comb. nov., exhibits an elongate snout with characteristics known in stem and crown archosaurs, including a downturned premaxilla and fluted teeth. We included R. sixmilensis in a phylogenetic analysis of archosauromorphs consisting of 677 characters and 109 taxa under both parsimony and Bayesian models. We recover R. sixmilensis as a doswelliid, sister to Doswellia kaltenbachi. Our parsimony and Bayesian models differ in the placement of Doswelliidae, either as sister to or within Proterochampsidae, respectively. We use archosauromorph relationships from the Bayesian model to estimate cranial disparity between stem and crown archosaurs and find a narrow breadth of morphological disparity in the stem. Our results suggest that crown archosaurs evolved disparate crania from a low-disparate archosauriform condition.

Snout

10.6084/m9.figshare.12409010

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Late Triassic tanystropheids (Reptilia, Archosauromorpha) from northern New Mexico (Petrified Forest Member, Chinle Formation) and the biogeography, functional morphology, and evolution of Tanystropheidae

Figshare (2015)

Adam C. Pritchard Alan H. Turner Sterling J. Nesbitt Randall B. Irmis Nathan D. Smith

ABSTRACTWe 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, postdating Tanytrachelos in the eastern United States. A new phylogenetic analysis of early saurians identifies synapomorphies of tanystropheid subclades, which are recognized in the recovered vertebrae and a calcaneum. The femora are consistent with referral to Tanystropheidae. There is no clear association of the remains, however, so we refrain from erecting a new taxon. The analysis also indicates that the Hayden Quarry tanystropheid fossils belong to a newly recognized clade including the Late Triassic taxa Langobardisaurus and Tanytrachelos. Because most tanystropheid specimens are two-dimensionally crushed skeletons, the Hayden Quarry tanystropheid fossils provide valuable insights into the three-dimensional osteology of derived tanystropheids. The most striking feature of the Hayden vertebrae is a rugose, flattened expansion of the neural spines in the dorsal, sacral, and caudal regions, probably linked to a ligamentous bracing system. These fossils and others from Late Triassic sites in the American West suggest that tanystropheids underwent a previously unrecognized radiation in North America just prior to their extinction.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Morphology

10.6084/m9.figshare.1332515

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A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria

The Science of Nature (2016)

Li Chun Xiao‐Chun Wu Li-Jun Zhao Sterling J. Nesbitt Michelle R. Stocker

10.1007/s00114-016-1418-4

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Citations (24)

A large-bodied silesaurid from the Lifua Member of the Manda beds (Middle Triassic) of Tanzania and its implications for body-size evolution in Dinosauromorpha

Gondwana Research (2014)

Paul M. Barrett Sterling J. Nesbitt Brandon R. Peecook

10.1016/j.gr.2013.12.015

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Citations (32)

Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda)

Proceedings of the Royal Society B Biological Sciences (2006)

Sterling J. Nesbitt Mark A. Norell

Living archosaurs comprise birds (dinosaurs) and crocodylians (suchians). The morphological diversity of birds and stem group dinosaurs is tremendous and well-documented. Suchia, the archosaurian group including crocodylians, is generally considered more conservative. Here, we report a new Late Triassic suchian archosaur with unusual, highly specialized features that are convergent with ornithomimid dinosaurs. Several derived features of the skull and postcranial skeleton are identical to conditions in ornithomimids. Such cases of extreme convergence in multiple regions of the skeleton in two distantly related vertebrate taxa are rare. This suggests that these archosaurs show iterative patterns of morphological evolution. It also suggests that this group of suchians occupied the adaptive zone that was occupied by ornithomimosaurs later in the Mesozoic.

Theropoda

Postcrania

10.1098/rspb.2005.3426

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Citations (131)

The origin and early radiation of dinosaurs

Earth-Science Reviews (2010)

Stephen L. Brusatte Sterling J. Nesbitt Randall B. Irmis Richard J. Butler Michael J. Benton

Pangaea

Supercontinent

Extinction (optical mineralogy)

Earth history

10.1016/j.earscirev.2010.04.001

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Citations (280)