A new drepanosauromorph (Diapsida) from East–Central New Mexico and diversity of drepanosaur morphology and ecology at the Upper Triassic Homestead Site at Garita Creek (Triassic: mid-Norian)

ABSTRACT

The Late Triassic was home to great tetrapod diversity, with a mixture of endemic Triassic groups and others with extant descendants. These two groups are represented in microvertebrate accumulations, but their fossils are mixed and fragmentary, leading to challenges in confidently identifying them. Among the Triassic endemic groups, drepanosauromorphs are among the most unusual and easily recognized, but many details of their anatomy are obscured by the lack of three-dimensional and matrix-free specimens. Here we describe new material, including a new species, using isolated but three-dimensional drepanosauromorph elements from the Homestead Site at Garita Creek, an Upper Triassic microvertebrate locality near Garita Creek, New Mexico. This site has thus far yielded dozens of isolated drepanosauromorph specimens, including manual/pedal unguals of at least three morphotypes, vertebrae, and caudal unguals (= tail claws). At least two drepanosauromorph species are present based on distinct enlarged ungual morphotypes, with one representing a new Skybalonyx-like species, Unguinychus onyx gen. et sp. nov., and a second form similar to Drepanosaurus. Unguinychus onyx may have been fossorial whereas the second morphotype likely represents an arboreal species, possibly indicating that contemporary drepanosauromorphs had different ecologies. For the first time, we report a potential “small” ungual morphotype, and we present a partial caudal ungual exhibiting features distinct from manual and pedal unguals. The identification of isolated and three-dimensional drepanosauromorph fossils expands the diversity of the clade and demonstrates the usefulness of incorporating microvertebrate data into assemblage studies.

ACKNOWLEDGMENTS

The Lauer Foundation for Paleontology, Science, and Education has generously provided access to the Homestead Site at Garita Creek and the existing collections from it. The Lauer Foundation (PSE) is proud to demonstrate the benefits that can be achieved through the collaborative and cooperative efforts between avocational paleontologists, private collectors, the Lauer Foundation, and academic institutions and museums to advance our understanding of the fossil record. We also thank L. and B. Martin for collection and preliminary identification of specimens. Michelle Stocker of Virginia Tech has provided valuable aid in identification of elements from Homestead. We thank S. Wills, P. Barrett, and D. Ward of the Natural History Museum in London for collaboration throughout the Homestead project. AppPaleo’s Finding Fossils on Friday group has been particularly helpful in sorting and identifying specimens, notably J. Crothers, L. Rose, S. Ahmed, J. Meyer, S. Randleman, Z. Ore, A. Wurtz, R. Dunn, J. Crouch, J. Heidenfelder, T. Walker II, and many more. The VT Paleobiology research group has also provided valuable feedback during this project, especially Megan Sodano and Ben Kligman (who provided scans of Skybalonyx skapter). We additionally thank R. Mueller and J. Socha for facilitating μCT scanner access at Virginia Tech for scanning of S. skapter specimens and PEFO staff and interns for their field and lab efforts that led to the existence and availability of these fossils. Funding for undergraduate research (IP) was provided by the L. Raymond fund and Triassic Trip Scholarship for fieldwork, the Appalachian State University Office of Student Research for travel, the Appalachian Department of Geological and Environmental Sciences in the form of an Undergraduate Research Assistantship, and the National Science Foundation through the S-STEM program. Additional graduate funding (IP) has been provided by the National Science Foundation Graduate Research Fellowship Program. Additionally, we thank the Museo di Scienze Naturali Bergamo for allowing study of the holotypes of Drepanosaurus unguicaudatus and Vallesaurus cenensis. Lastly, we greatly thank our reviewers and handling editors for valuable feedback. This is contribution 9 from the Homestead at Garita Creek project.

AUTHOR CONTRIBUTIONS

IP designed the project and drafted the manuscript. SJN provided preliminary identifications and numerous suggestions for descriptions and figures. ABH established initial contacts with Larry Martin and the Lauer Foundation for Paleontology, Science, and Education, aided with early project organization, and coordinated and/or conducted relevant fieldwork. RL and BL provided a specimen repository, institution catalog numbers, and drafted provenance information, with additional information added by ABH. All authors edited the manuscript.

DATA AVAILABILITY STATEMENT

The raw and segmented CT data for Skybalonyx skapter holotype PEFO 43703 and Skybalonyx skapter specimens PEFO 44760 and PEFO 44761 referenced in this study are available on MorphoSource: https://www.morphosource.org/projects/000580888?locale=en.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).