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Journal of Paleontology 90(1):154–169
the back of the tooth alveoli, the transverse ventral profile of the rostrum is convex ventrally.
Premaxilla.—That portion of the left premaxilla that preserves the premaxillary sac fossa, the posteroexternal plate and the posterointernal process are all that remain. In dorsal view (Fig. 3.1, 3.3), the medial and lateral margins of the bone are nearly parallel on either side of the sac fossa. Contralateral premaxillae, at least in the area that is preserved, did not cover over the mesorostral canal giving the impression that it was open throughout its length. The premaxillary foramen is not preserved, however the posterolateral sulcus is, and it closely parallels the lateral margin of the bone through much of its length but disappears within the area of the posteroexternal plate. Medial to the posterior moiety of the sulcus is the pre- maxillary cleft that cuts a trough up to 5mm deep as it courses posteromedially toward the posteroexternal plate (Fig. 3.1, 3.3). A sigmoid-shaped suture is formed between the posterior margin of the premaxilla and maxilla that separates the posteroexternal plate from the posterointernal process.
Maxilla.—In dorsal view lateral to the premaxilla, two maxillary foramina (i.e., dorsal infraorbital foramina; the ante- riormost one is 2mm in diameter, the other 3.5mm) occupy the space immediately anterior to the antorbital notch (Fig. 3.1, 3.3). Much of the overlapping supraorbital portion of the maxilla was not preserved. However, posterior to the sigmoid-shaped suture, some of the posteriormost part of the maxilla that overlapped the frontal remains.
Frontal.—The skull is broken through the frontals where they suture with the maxillae and nasals (the latter of which are not preserved). In dorsal view (Fig. 3.3, 3.4), the lateral margin of the supraorbital margin of the frontal forms a straight border. The surface of the supraorbital region is coarsely textured having been covered by the maxilla in life. The postorbital processes were not preserved. On the anterior part of the cranial half of the skull, contralateral parts of the frontals abut/suture along their shared midline. On either side of the suture are clusters of tiny supraorbital foramina; between 0.5-1mm in diameter. Lateral to these are the linear furrows that held the posteriormost extremity of the maxilla. The transverse coronal (i.e., frontoparietal) suture zigzags across the tabular inter- temporal region of the skull. In ventral view (Fig. 4.2), a tight cluster of at least six
frontal foramina open in the roof of the orbit just anterior to the postorbital ridge. The optic infundibulum (and orbital fissure) lies immediately medial to these foramina (Fig. 4.1, 4.2).
Parietal.—The tabular intertemporal face of the parietals preserves four posterolateral foramina at the level of the anterodorsal reach of the supraoccipital (Fig. 3.2, 3.4). There is no suggestion of a sagittal crest along the midline of the parietals. Below the concave dorsolateral margin of the parietal, the bone sweeps ventrolaterally to suture to the squamosal along an antero-ventrolaterally trending trough. At the point where the suture approaches the posterior margin of the intertemporal fossa, the parietal is bound ventrolaterally by a 10-mm-wide strip of the alisphenoid (as preserved), which in turn forms the
subtemporal crest. Above this sutural contact, the concave lateral face of the parietals exhibit several shallow vascular furrows (Fig. 3.4).
Squamosal.—The squamosal seems to contribute little to the lateral wall of the braincase. In dorsal view the suture between the parietal and squamosal lies along the floor of the temporal fossa. This fossa separates the lateral wall of the braincase from the zygomatic process of the squamosal. In dorsal view (Fig. 3), the zygomatic process is convex laterally and pointed anteriorly. It appears to have formed the widest part of the skull. In lateral view, it is convex dorsally and concave ventrally. For the most part, the surface of the bone is featureless. Ventrally, the external auditory meatus lies immediately
posterior to the postglenoid process (Figs. 4.3, 6). Medially, the wedge-shaped spiny process is formed by the converging anterior and posterior meatal crests. The long axis of the auditory meatus points directly toward the fenestra ovalis in the periotic (Figs. 4.3, 6). Anterior to the spiny process is the space occupied by the middle sinus (as seen in Simocetus; Fordyce 2002, fig. 15). Medially, this second wedge-shaped area opens directly into the fossa incudis on the periotic. From this point forward, the falciform process takes shape. Unfortunately, neither process is complete. In SC 2015.51.1 (Figs. 4.3, 6), the complete left periotic lies immediately medial to the spiny process, the middle sinus, and the falciform process.
Supraoccipital.—The supraoccipital figures prominently on the dorsal and posterior sides of the skull in SC 2015.51.1a (Figs. 3.2, 3.4, 4.4). Its anterodorsal margins (i.e., its apex) form a right-angle wedge separating the posterolateral foramina on the parietals. Here the thickness of the supraoccipital is barely raised above the level of the parietals. The apex lies to the left of the center of the tabular parietals, suggesting a slight degree of cranial asymmetry. Posterolaterally, the nuchal/lambdoid crest overhangs the parietal, squamosal, and exoccipital. Ventrally, the crest takes a sharp turn anterolaterally onto the zygomatic process of the squamosal where it soon disappears into the body of that bone. In general, the posterior surface of the supraocci- pital is concave. However, a number of obvious protuberances rise from its surface and presumably mark the site of origin of epaxial musculature (including m. semispinalis). The external occipital crest is more accurately described as a midline protu- berance within the anterodorsal third of the bone. Posteroventral to this protuberance the supraoccipital exhibits its most conspicuous concavity. Ventrally, the supraoccipital is inextricably fused to the exoccipital.
Exoccipital.—The occipital condyles are twice as wide as they are high (Fig. 4.4). The condyles stand out on pedicles that nearly form a continuous concave trough around the perimeter of the condyles. A cluster of at least four foramina, approxi- mately 1mm in diameter, occupy the posterior face of the left exoccipital opening immediately lateral to the condyle (Figs. 3.2, 3.4, 4.3–4.5).
Periotic.—Both periotics are preserved in situ contacting the squamosal (laterally), alisphenoid (anteriorly), parietal (dorso- medially), and paroccipital process posterodorsally (Figs. 6, 7).
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