170


Journal of Paleontology 91(1):162–178 We consider a sliver of an element anterior to the


quadratojugal as part of the dentary. This element is only visible in occlusal view and bears the medial portion of as many as three tooth sockets (only one well preserved) and as such is strongly suggestive of it being the dentary. However, sometimes in basal archosauriforms the splenial contributes to the medial margin of posterior tooth sockets, so we cannot unequivocally exclude the possibility that it represents the anteromedial portion of the splenial (e.g., some phytosaurs, see Heckert et al., 2013), but this is not known to occur in aetosaurs. It is not identified on any figures because it is tucked so deeply into the preserved specimen that it is not visible in any of the views we can provide. The surangular is extended posteriorly into a short retro-


articular process. As best seen on the right side (Fig. 5.3, 5.4), it splits anteriorly into two processes that bound the posterior half of the mandibular fenestra. There is a shallow groove along the dorsal margin of the angular that receives the ventral process of the surangular so that the articulation between the two elements is more of a “tongue and groove” and less a simple butt joint. A small fragment of bone lying immediately above the retroarticular process may represent the articular (Fig. 5.4). Dentition.—All or parts of six teeth are associated with the


specimen. None are in place, having fallen out of their sockets, but all are in the oral cavity in that they are between the mand- ibles and in front of the (now) vertically oriented palate. They are small (millimeter scale), but of a size consistent with that of the specimen. Furthermore, some preserve roots and thus were not shed and therefore are unlikely to be from another animal. The most clearly seen is in the oral cavity when viewed in ventral aspect (Fig. 4.3, 4.4). All are essentially conical, not bulbous, and lack serrations. Some are only slightly recurved, with the curvature restricted to a point near the apex, whereas other teeth are more recurved, in a pattern similar to that of phytosaurs. None are particularly tall, with the most complete crown no more than twice as tall as its basal length. Fragments of additional, similarly-sized, teeth are embedded in the mandibular sockets, but are not preserved sufficiently to describe further.


Axial skeleton.—The largely articulated carapace obscures much of the axial skeleton, as it does in Coahomasuchus kahleorum (Heckert and Lucas, 1999) and other articulated aetosaur specimens. In dorsal aspect (Figs. 2.1, 3.1), two rod- like elements that are probably ribs are visible, as is much of the shaft of the right (?) scapula and a fragmentary neural arch that lies posterior and ventral to the seventh paramedian and is not visible in the figures. In ventral aspect more of the axial skeleton is visible,


including several centra and fragments of ribs and gastralia (Figs. 2.2, 3.2). A disrupted area in the left portion of the body cavity reveals parts of six dorsal centra, all in ventral view. Four are nearly in articulation, and each of these is somewhat shorter (~15mm long) and stouter (up to 6mm across the middle of the centrum) than the more complete of the other two centra, which is significantly longer (≥20mm) and has a more pinched (≤5mm wide) centrum. The more elongate dorsal centrum is unlike the known centra of C. kahleorum in possessing a keel consisting of an extremely narrow ridge along the ventral


surface (Fig. 2.2). Afew nearby fragments appear to be portions of the ribs, as they have ovoid cross-sections and are parallel to one another. All are strongly displaced from the midline of the carapace, and so their anatomical position within the skeleton is unclear.


Near a gap in the posterior ventral carapace along the


midline there are the remnants of three bones we interpret as gastralia as they are rod-like and more gracile than the ribs. None are complete, but the best example preserves a typical 120˚ concave posteriorly chevron-like shape, similar to that documented in Typothorax coccinarum (Heckert et al., 2010). It is not clear if any of the other elements are the more medial gastral elements, but this is the second report of gastralia in aetosaurs. Nesbitt (2011) mistakenly coded aetosaurs as lacking gastralia, but we suspect that this is more likely an artifact of preservation.


Appendicular skeleton.—Only the anterior portions of the appendicular skeleton are preserved, and even these are largely covered by armor. We are able to provide brief descriptions of the scapula and humerus, however. Scapula.—A portion of one scapula, which we interpret as


the right, is visible through the disrupted armor on the right side of the carapace in dorsal aspect (Figs. 2.1, 3.1). The visible portion includes most of the shaft, but no glenoid (which is under a displaced paramedian osteoderm) or distal-most extre- mity of the blade (also under osteoderms), and it lies over parts of the exposed two ribs. The blade expands in both directions from the distal shaft, with the posterior expansion beginning lower on the shaft than the anterior expansion. Humerus.—Much of the left proximal humerus and shaft is


visible in ventral aspect (Figs. 2.2, 3.2). Proximally, the head is convex, with an anterior margin that slopes down to the delto- pectoral crest and a posterior margin that intersects the shaft to form a broad (140°) angle. The deltopectoral crest is large but not particularly prominent or distinct, and is expressed as a wider region on the anterior portion of the bone. The distal humerus is not exposed. Comparison to the right side, which is almost completely encased in armor other than parts of the head and distalmost portion, demonstrates that the humerus was probably ~70mm long. Appendicular osteoderms cover other elements, although a sliver of either the left ulna or radius may be exposed posterior to the humerus on the ventral surface.


Armor.—The armor of the holotype specimen is exposed in both dorsal and ventral aspects, and includes much of both columns of the anterior dorsal paramedian osteoderms, some lateral osteoderms, many ventral osteoderms, and extensive, articulated appendicular armor that obscures most of the forelimbs, as well as a posterior paramedian removed during preparation. There are a few small, poorly preserved osteoderms posterior to the skull in ventral view that may represent gular osteoderms similar to those of Coahomasuchus kahleorum (Fig. 4.3, 4.4). In addition to the articulated specimen, there are a variety of osteoderms represented in the material that we refer to Coahomasuchus, including isolated paramedians, laterals, ventral, and appendicular osteoderms. Of these, three para- medians and a representative lateral osteoderm are illustrated in Figure 6. Most of the paramedians, including one taken from the


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