A new aetosaur (Archosauria, Suchia) from the Upper Triassic Pekin Formation, Deep River Basin, North Carolina, U.S.A., and its implications for early aetosaur evolution

ABSTRACT

Aetosaurs are an extinct clade of quadrupedal, heavily armored archosaurs that had a worldwide distribution during the Late Triassic. Aetosaur fossils from the Upper Triassic Pekin Formation in the Deep River Basin of North Carolina (U.S.A.) consist primarily of isolated osteoderms and, rarely, more associated material. Here we describe a new genus and species, Gorgetosuchus pekinensis, based on an associated incomplete anterior carapace, consisting of a total of 19 nearly complete paramedian and lateral osteoderms from the first 10 rows of armor as well as some associated fragments. An important feature of Gorgetosuchus is that an articulated fifth row of cervical osteoderms almost encloses the neck, with prominent spines on both the dorsal and lateral osteoderms. This is a novel configuration among aetosaurs. Otherwise, NCSM 21723 preserves a mosaic of character states found in Longosuchus, Lucasuchus, or both taxa while simultaneously preserving several more plesiomorphic character states, such as cervical osteoderms that are wider than long. Our reevaluation of other Pekin Formation specimens that various authors have assigned to Desmatosuchus, Longosuchus, or Lucasuchus confirms that some possess characteristics of Lucasuchus, whereas others are not generically determinate. Incorporating Gorgetosuchus into existing phylogenies of aetosaurs results in a reshuffling of basal aetosaur relationships, but a variety of analyses consistently place Gorgetosuchus as a basal desmatosuchine. Using current taxonomic practices, there are at least three aetosaur genera in the Pekin Formation: Lucasuchus, Coahomasuchus, and Gorgetosuchus.

http://zoobank.org/urn:lsid:zoobank.org:pub:5503A4F4-85DE-4B47-9E58-6C9F903A1640

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

ACKNOWLEDGMENTS

Volunteers and staff at the NCSM, including J. Adams, L. Bailey, and C. Zidar, helped find and collect the fossils described here. L. Bailey also assisted in the preparation of these specimens. We thank the company that owns the property, although they wish to remain anonymous. S. Nesbitt provided casts and photographs of specimens of both Longosuchus and Lucasuchus from the TMM collections. M. Norell and C. Mehling (AMNH) and K. Padian and P. Holroyd (UCMP) facilitated loans. W. Parker helpfully answered several questions regarding character construction in his analyses. Photography was accomplished by the authors (A.B.H. and V.P.S.) and R. Chandler of the NCSM. Z. Murrell provided thoughtful discussion regarding parsimony and likelihood analyses. Discussions with P. Olsen clarified the stratigraphy of the quarry area. J. B. Desojo and W. G. Parker provided helpful reviews of an earlier version of the manuscript, which was handled by editor R .B. Irmis, who also provided constructive comments. Discussions with J. B. Desojo and M. B. Baczko improved the phylogeny presented here. These discussions and firsthand comparisons with South American fossils were facilitated by support to A.B.H. from the Appalachian State University Board of Trustees International Research Grant and University Research Council.

Handling editor: Randall Irmis.