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Journal of Paleontology 91(1):162–178


Parker, 2016), approximately two-thirds of the presacral skeleton is preserved. Dorsal and ventral osteoderms are largely in articu- lation and some of the appendicular osteoderms covering the forelimbs are preserved (Figs. 2, 3). A few postcranial elements, including parts of both humeri and a scapula are exposed, as are several vertebrae (Figs. 2, 3). However, because much of the carapace is articulated it almost certainly includes additional postcranial elements that are concealed between the dorsal and ventral armor. Parts of the left and right forelimbs are also present, but largely obscured by appendicular osteoderms. The carapace over the right shoulder region has been compromised so that a large part of a right (?) scapula can be seen (Fig. 3.1). The ventral surfaces confirm that the specimen has been


greatly compressed, and posteriorly much of it is missing (Figs. 2.2, 3.2). The overwhelmingmajority of the bones exposed in ventral view are osteoderms, principally of the ventral armor but including appendicular osteoderms associated with both forelimbs. From this perspective portions of both forelimbs are visible, and a few vertebrae and even the ventral surface of some paramedian osteoderms are visible where the carapace has been compromised on the animal’s left side (Fig. 3.2), and a paramedian from this area was completely removed and cleared of matrix to expose its dorsal surface. The articulation between the osteoderms disintegrates about half way down the length of the body at a point anterior to the sacrum. There is no indication of any sacral or more posterior material.


Cranial elements.—We describe the preserved portions of the skull (Figs. 4, 5), which is somewhat damaged and dis- articulated, and therefore difficult to interpret, in general terms before describing each of the preserved elements in more detail. For the most part, only the posterior part of the skull, from a point close to the orbits, is preserved in NCSM 23618. It is somewhat crushed, and the mandibles have rotated forward


relative to the suspensorium. As a result, the quadrates are lying flat (ventral portions facing anteriorly, see Fig. 4.3, 4.4) and even below the level of the palate, and the palate has been pushed posteriorly and dorsally through the skull roof, so that it is now oriented vertically. Although there is significant dis- articulation of many cranial elements, some clear associations of individual bones remain. None of the skull openings (nares, orbits, fenestrae) are intact, and we cannot say anything at all about the nares or antorbital fenestra. In general, the elements comprising the temporal region are more completely preserved, but disarticulated from one another. Because of crushing it is difficult to distinguish between fractures and true articulation margins or sutures, but it does not appear that much, if any, of the skull sutures were completely fused, so the individual was almost surely not fully grown. Thus, in spite of crushing and disarticulation, many


Figure 3. Interpretive sketches of the holotype specimen of Coahomasuchus chathamensis n. sp. (NCSM 23618) in (1)dorsal and (2) ventral aspects. ang = angular; app = appendicular osteoderms; bc = braincase; dpm = dorsal paramedian osteoderm; g = gastralia; h = humerus; j = jugal; lat = lateral osteoderm; n = nasal; p = parietal; po = postorbital; q = quadrate; qj = quadratojugal; r = ribs; sa = surangular; sc = scapula; sq = squamosal; v = vertebral centrum. ? indicates uncertainty. Numbers in (1) refer to rows of dorsal paramedian osteoderms; r1/l1, r2/l2, r3/l3, r4/l4 in (2) refer to right and left, respectively, columns of ventral osteoderms. Shading indicates matrix from the block containing the skeleton. Scale bars represent 5 cm.


individual skull elements can be positively identified. These include all or parts of the right nasal, frontal, parietal, and squamosal, possibly part of the left frontal and squamosal, and all or parts of both jugals, postorbitals, quadratojugals, quadrates, and pterygoids, together with the basisphenoid (Figs. 3–5). Lower jaw elements that are discernable include portions of both angulars and surangulars (Figs. 4, 5). The descriptions of skull and jaw elements in subsequent paragraphs


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