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Journal of Paleontology 91(1):162–178
to accurately present a reasonable hypothesis for the phyloge- netic position of Coahomasuchus. We have evaluated Parker’s (2016) phylogeny, in parti-
cular his coding of Coahomasuchus, although we reserve judgment on his referral of the unpublished and undescribed “carnivorous aetosaur” specimen (TMM 31100-437) to Coahomasuchus kahleorum. This specimen is not available to us for study, has only appeared in the literature in an abstract (Murry and Long, 1996), and is neither illustrated nor described by Parker (2016), so we do not include it in our list of specimens. It is apparent from close examination of Parker’s (2016) matrix that this specimen is critical to his concept of Coahomasuchus, and that many of his codings, particularly of cranial, jaw, and dental material, are based on his observations of TMM 31100-437. It is from the same area (Otis Chalk) and stratigraphic unit (Colorado City Formation of our usage) as the holotype of Coahomasuchus kahleorum, so it adds little if anything to the paleogeographic range and stratigraphic distribution of the genus. Like Heckert et al. (2015), Parker (2016) found that
Aetobarbakinoides, not Coahomasuchus, is problematic, largely because its osteoderms are almost entirely unknown and thus cannot be scored nor provide insight to its relationships with the many taxa known solely from osteoderms. Otherwise, the observable features of the holotype of C. chathamensis score identically to C. kahleorum, with the exception of the maximum width of the paramedian osteoderms, so the addition of this new species is unlikely to change the phylogenetic position of the genus.
Distribution and age.—Previously, the only published speci- men of Coahomasuchus was the holotype of C. kahleorum from the Colorado City Formation of West Texas. This marks the first occurrence of Coahomasuchus from outside the American Southwest. The Pekin Formation of North Carolina shares the presence of another aetosaur, Lucasuchus, with the Colorado City Formation as well (Parker and Martz, 2010). This rein- forces past correlations of lowermost “Dockum” strata in Texas with the Carnian-aged portion of the Newark Supergroup (e.g, Lucas and Huber, 2003). In this case the correlation is established at the genus level, not the species level, but it is nonetheless indicative that at least some Upper Triassic strata in the American Southwest may in fact be Carnian, not Norian, in age, regardless of the duration of the Norian.
Conclusions
Coahomasuchus chathamensis from the Pekin Formation of NorthCarolina is the first occurrence of the genus fromoutside of the American Southwest, the second aetosaur named from the Pekin Formation, and only the second aetosaur identifiable to species fromNorth Carolina. The carapace is the stratigraphically oldest record of a wide-bodied aetosaur (W:L of dorsal para- median osteoderms≥3.5:1), although it is too incomplete to determine if it had the fully discoidal carapace that characterizes taxa such as Typothorax and Paratypothorax. Finally, because aetosaur skulls are relatively uncommon, the skull described here provides additional insight into morphological features, not just of Coahomasuchus, but of aetosaurs generally.
Acknowledgments
Volunteers and staff at the NCSM, including V. Lee and T. Weaver, helped find and collect the fossils described here. We thank the company that owns the property, although they wish to remain anonymous. R. Chandler executed some of the photographs of the specimen. The NMMNH provided a cast of the holotype of Coahomasuchus kahleorum for comparison. Discussions with P. E. Olsen clarified the stratigraphy of the quarry area. M. Celeskey provided additional information from his study of the holotype of C. kahleorum. Reviewers W. Parker and T. Sulej provided helpful reviews of an earlier version of this manuscript, which was handled by editors B. Hunda and M. Langer.
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