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Journal of Paleontology 91(1):162–178
right frontal, but may include part of the left. The portion visible in dorsal view is lightly ornamented with several shallow pits like the nasal(?) and includes smaller, proportionately deeper pits and thus is more ornamented. The visible bone includes a tapering posterolateral margin we interpret as the medial margin of the orbit. The right parietal is present, but mostly obscured by the
anterior-most paramedian osteoderms (Fig. 4.1, 4.2). We interpret one portion, visible behind the displaced nuchal osteoderms, as the anterior margin of the right parietal and its suture with the posterior portion of the right frontal. Posterior to the third right paramedian osteoderm is an elongate process we interpret as the lateral portion of the posterior flange of the parietal (Fig. 5.3, 5.4). This process curves laterally toward the posterior margin of the disarticulated postorbital and squamosal. Only the posterior parts of both jugals (Figs. 3–5) are
preserved, each best seen in lateral view. They are robust elements that formed the anterior margins of the lower temporal fenestrae. Posteriorly this bone splits into well-defined dorsal and ventral processes, as in Stagonolepis, Aetosaurus, and Stenomyti (Walker, 1961; Small and Martz, 2013), but unlike other most aetosaurs for which the jugal is known (e.g., Desojo and Báez, 2007, text-fig. 5; Parker, 2016; Schoch and Desojo, 2016). A thin ridge or keel divides the two posterior processes; the more ventral process is significantly longer and more robust than the dorsally directed postorbital process. The right postorbital (Fig. 5.3, 5.4) is gently arcuate with
the addition of a poorly developed spur on a keel for its articulation with the squamosal on the posterior side. The posterior border of the orbit is slightly raised into a rim, and there is a pronounced facet on the dorsal process where it was presumably overlapped by the postfrontal. Our preferred restoration (Fig. 5.4) is based on all three elements on the right side being essentially complete, but somewhat disarticulated, with the postorbital rotated 90˚ counterclockwise relative to the squamosal. The left postorbital is poorly and incompletely preserved (Fig. 5.1, 5.2), but does show the small, pointed posterior process but otherwise provides no additional resolution. We interpret an “L-shaped” bone best seen in dorsal
(superior) aspect as the right quadratojugal (Figs. 3.1, 4.1, 4.2, 5.3, 5.4). The posterolateral corner is rounded and projects more ventrally than the rest of the bone. The dorsal process is clearly faceted, with an anterior facet that the postorbital overlapped and another that articulated with the squamosal dorsally and posteriorly. As preserved, it is not as tall as the postorbital, but taller than the squamosal. Anterior to the quadratojugal is a sliver of bone of uncertain affiliation that we tentatively interpret as a portion of the right dentary. Parker (2016, character 17)
Figure 5. Photographs (1, 3) and interpretive sketches (2, 4) of the holotype skull of Coahomasuchus chathamensis n. sp. (NCSM 23618) in (1, 2) left lateral and (3, 4) right lateral aspects. All elements are from the side of view unless otherwise noted. a = angular; ar = articular; dpm = dorsal paramedian osteoderm; f = frontal; j = jugal; lat = lateral osteoderm; n = nasal; nu = nuchal (first paramedian) osteoderm; p = parietal; pfl = parietal flange; po = postorbital; q = quadrate; qf = quadrate foramen; qj = quadratojugal; sa = suragular; sq = squamosal; numbers refer to rows of osteoderms; ? indicates uncertainty. (l) and (r) refer to left and right sides, respectively. Scale bars represent 2 cm.
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