zalambdalestes - American Museum of Natural History

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44 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 281 Fig. 19. Stereophotograph of the skull of Zalambdalestes lechei PSS-MAE 130 in dorsal view, with accompanying line drawing. Gray pattern represents matrix. Abbreviations: ch, cerebral hemisphere; fr, frontal; ju, jugal; lac, lacrimal; mx, maxilla; na, nasal; naf, nasal facet on frontal; ob, olafactory bulb; pa, parietal; pal, palatine; pmx, premaxilla; sq, squamosal; ssf, subsquamosal foramen; sss, superior sagittal sinus; ts, transverse sinus; ver, vermis of cerebellum. ilar orientation to those in PSS-MAE 108 and 130. The palatal processes of the maxillae are nearly complete in PSS-MAE 130, the major damage being an artifactual hole immediately anterior to the palatine bone (figs. 8A, 35. The maxillae form two elongate, shallow, concave surfaces on either side of the midline. Anteriorly, they taper to a narrow pointed end at the level of the I2 alveolus that is inserted into a V-shaped notch between the two premaxillae. As evidenced by PSS-MAE 108 and AMNH 21708 (fig. 32), there is a low, raised ridge on the anterior part of the
2004 WIBLE ET AL.: ZALAMBDALESTES 45 Fig. 19. Continued. intermaxillary suture that ends at the level of the canine. Only the rostralmost part of the intermaxillary suture in PSS-MAE 130 shows this ridge; behind that the left and right maxillae have been separated postmortally to a slight extent (figs. 7, 8A). Based on ZPAL MgM-I/14 and 16, Kielan-Jaworowska (1984a) reported a major palatine foramen (her greater palatine foramen) in the maxilla opposite the protocone of P3 with a very short groove extending forward from it (fig. 4D). The major palatine foramen in PSS-MAE 130 differs in two regards (figs. 8A, 35). First, it is slightly more posterior, more so on the left than on the right, opposite the posterior part of the P3. Second, it is double, with a smaller posterolateral opening separated by a narrow bridge from a larger anteromedial opening, which has a short, faint groove extending forward from it. There is a major palatine foramen on the right side of AMNH 21708 (fig. 32). As preserved, it is a single large opening and is even more posterior than in PSS-MAE 130, opposite the protocone of P4 (figs. 4C, 32). A second smaller opening appears to lie opposite the protocone of M1 (not figured by Van Valen). The nature of this second aperture is unclear (a second major palatine foramen, an accessory palatine foramen, or artifact); PSS-MAE 130 shows no such opening, but its palate is damaged in this region (figs. 8A, 35). The horizontal portion of the palatine bone has been poorly known for Zalambdalestes, but most of it is well preserved in PSS-MAE 130; the exception is the anterior portion, which is missing as is the posteromedial portion of the maxillae (figs. 8A, 35). As reconstructed here, the palatal processes of the palatines are proportionally very small (fig. 43), smaller than the elements reconstructed by Kielan-Jaworowska (fig. 4D; 1984a: fig. 1) for Zalambdalestes based on Barunlestes. It also does not appear to contain any accessory palatine foramen (lesser palatine foramen of Kielan-Jaworowska) near its anterior margin or a more central location, such as those included in the reconstructions in Van Valen (fig. 4C; 1964: fig. 2) and Kielan-Jaworowska (fig. 4D; 1984a: fig. 1). The lateral suture with the maxilla can be discerned on the left side of PSS-MAE 130 (figs. 8A, 35). It runs longitudinally medial to the molars. Only the posterior portion of the suture itself, between the minor palatine foramen (posterior palatine foramen of Kielan-Jaworowska, 1984a) and the M2, is preserved. Anterior to this to the level of the M1 protocone, there is a ridge on the maxilla that indicates where the palatine abutted, but that bone is missing in this interval. We were unable to identify the palatines’ anterior suture with the maxillae, at least in part because of damage that resulted in a gaping hole. We tentatively reconstruct that suture near the anteriormost preserved limit of the palatine, at the level of the mesial edge of M1 (fig. 43). A raised ridge runs the length of the preserved inter-
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