Heckert et al.—New species of Coahomasuchus from North Carolina
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Figure 6. Dorsal paramedian (1–3) and lateral (4, 5) osteoderms referred to Coahomasuchus chathamensis from NCPALEO 1902. All are from the right side of the body. (1) Anterior dorsal or posterior cervical paramedian (NCSM 21707) in dorsal view. (2) Anterior dorsal (thoracic) paramedian osteoderm (NCSM 16444-1) in dorsal view. (3) Thoracic dorsal paramedian in matrix (NCSM 19675) in dorsal view. (4) Right lateral osteoderm (NCSM 21179) in external (~ dorso-lateral) view. (5) Impression of (4) in matrix from the site. Scale bars represent 2 cm.
coded Coahomasuchus as having a derived state wherein the jugal underlies the quadratojugal, which we interpret as possible based on the posteriorly forked processes of the jugal described previously, but which we cannot determine unambiguously on this specimen. The left quadratojugal is less well preserved and harder to see than the right because of the associated squamosal (?) and quadrate (Fig. 5.1, 5.2), but preserves the distinctive ventral projection. The right squamosal (Figs. 3.1, 5.3, 5.4) is a complexly
shaped bone that is very similar to that ofmost other aetosaurs. It possesses a pronounced posterolateral hook that would have formed the posterodorsal margin of the tympanic fossa. A shorter posteromedial process contributed to the posterolateral margin of the upper temporal fenestra and contacted the parietal. The long anteroventrally directed process is largely covered by the right postorbital, and as a consequence details of the articular facets for the postorbital and quadratojugal are obscured. A possible left squamosal is evident in lateral view (Fig. 5.1, 5.2) but poorly preserved and adds nothing to the discussion here. The quadrates (Figs. 3.2, 4.3, 4.4, 5) are large strut-like
elements that, although displaced downwards below the level of the basipterygoid, are still closely associated with the posterior ends of each mandible. These are some of the largest and most robust elements preserved in the skull. A prominent ridge runs dorso-ventrally along the posterior surface. The robust, approximately circular, articular condyle is best seen on the right side only slightly displaced from the articulation with the mandibular condyle. A deep anteromedial flange best seen on the left side is still in close association with part of the
posterolateral flange of the pterygoid (quadrate process of the pterygoid sensu Desojo and Baez, 2007). Unfortunately, we cannot unambiguously identify the quadrate foramen from the preserved material. Palate.—In ventral view large portions of both pterygoids are
still preserved in broad articulation with each other along the midline (Fig. 4.3, 4.4), although most of these elements are now vertically oriented and only visible in anterior aspect. The con- tacts with the stout basipterygoid processes are damaged on both sides, obliterating details of the nature of this articulation. The quadrate process of the pterygoid (sensu Desojo and Baez, 2007) is evident in posterior view medial to the left quadrate. Braincase.—On its ventral surface, the basisphenoid exhibits
a pronounced fossa, or basisphenoid recess (Figs. 3.2, 4.3, 4.4), that is relatively short and deep. The basipterygoid processes are comparatively long, but only slightly separated from the basal tubera (plesiomorphic condition of Parker, 2016). These tubera are stout and posteriorly directed, but their posterior facets are not well preserved and their relationship with the basioccipital is obscured by a small bone (hyoid?) laying on the ventral surface of the braincase. The metotic fissure may be visible on the lateral surface of the left basisphenoid (Fig. 4.3, 4.4). Comparisons to the holotype of Coahomasuchus kahleorum (Heckert and Lucas, 1999; Desojo and Heckert, 2004; see also Parker, 2014) are difficult due to relatively poor preservation ofNCSM23168. Lower jaw.—The posterior ends of the mandibles are
preserved on both sides with portions of each angular and surangular still in articulation with each other as well as being closely associated with the condyle on the quadrate (Figs. 3–5).
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