Heckert et al.—New species of Coahomasuchus from North Carolina


20799. All are from NCSMlocality NCPALEO1902, albeit were recovered in separate blocks from the holotype and doubtless represent at least one, and possibly multiple, other individuals.


Remarks.—In the following paragraphs, we highlight simila- rities and differences of the holotype of Coahomasuchus chathamensis with other known aetosaurs. We divide this dis- cussion into a brief summary of our interpretation of the skull and lower jaws, which are infrequently found with aetosaur specimens and not well understood, and a section on the osteoderms. The osteoderm discussion is critical because osteoderms are extremely important in understanding the taxo- nomy of aetosaurs (many taxa are known solely from osteoderms—Desojo et al., 2013; Heckert et al., 2015; Parker, 2016), and indeed, despite the completeness of this specimen, it is the osteoderms that verify its assignment to Coahomasuchus. Skull and jaws.—Skulls of aetosaurs remain relatively rare in


the Upper Triassic fossil record (Desojo et al., 2013), and are much rarer than those of coeval taxa such as phytosaurs (e.g., Long and Murry, 1995). Thus, the holotype skull of Coahomasuchus chathamensis, while incomplete, somewhat disarticulated, and difficult to interpret, retains important information. This is especially true because the skull of Coahomasuchus kahleorum is even more fragmentary (Heckert and Lucas, 1999; Desojo and Heckert, 2004; Parker, 2016). Relatively well-preserved and described skulls are known


for several of the less derived aetosaurs, including Stagonolepis robertsoni (Walker, 1961; Gower and Walker, 2002) and S. olenkae (Sulej, 2010), Aetosaurus (Walker, 1961; Schoch, 2007), Neoaetosauroides (Desojo and Baéz, 2007), and Stenomyti (Small and Martz, 2013). More derived aetosaurs are well represented by incomplete skulls of Desmatosuchus (Case, 1922; Small, 2002; Parker, 2005) and Longosuchus (Sawin, 1947; Parrish, 1994), undescribed skulls of Typothorax (Heckert et al., 2010; Parker, 2016) and a particularly complete skull and lower jaws of Paratypothorax (Schoch and Desojo, 2016). We rely on these authors’ descriptions for comparison, although we have examined many of these specimens first-hand as well. Since Walker’s (1961) exhaustive treatment of the skull of


Stagonolepis, many authors have considered that morphology to represent the aetosaurian bauplan, and many aetosaur skull reconstructions, even if skull material was not known or poorly preserved, were clearly based onWalker’s concept of Stagonolepis (e.g., Bonaparte, 1967; Long andMurry, 1995;Heckert and Lucas, 1999). Desojo and Baéz (2007) were the first modern workers to systematically evaluate the skulls of multiple taxa and show that therewas considerable diversity of aetosaur skull morphologies, an idea further developed by Desojo et al. (2013).We are not prepared to present a reconstruction of the entire skull of Coahomasuchus based on the new material, but detail insights it provides on the skull roof, temporal region, and lower jaws here (Fig. 7). Skull roof.—First, we note that, relative to Stagonolepis as


described by Walker (1961; see also Gower and Walker, 2002) the skull roof of Coahomasuchus would be lower and flatter.We base this on the fact that, in lateral view, only the lateral ridge of the nasal is visible, the rest is relatively depressed, more so than in Stagonolepis robertsoni (Walker, 1961, fig. 2). Additionally, although there is evidence of some ornamentation on the frontals and parietals of Coahomasuchus chathamensis,it is


Figure 7. Tentative reconstructions of the posterior portion of the skull of Coahomasuchus chathamensis in left lateral view. (1) Reconstruction with dashed lines showing inferred/reconstructed bones. (2) Interpretive sketches of elements (many reversed) from previous figures rearticulated to show the basis of the reconstruction. a = angular; ar = articular; inf = infratemporal fenestra; j = jugal; man = mandibular fenestra; po = postorbital; q = quadrate; qj = quadratojugal; sa = suragular; sq = squamosal; stf = supratemporal fenestra. Scale bar represents 2 cm.


173


faint and not as pronounced as in forms such as Stagonolepis olenkae (Sulej, 2010). Temporal region.—Secondly, the postorbital is likewise not


consistent with the condition reported in other aetosaurs, lacking a well-developed triangular process where it would have


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