zalambdalestes - American Museum of Natural History

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48 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 281 Fig. 21. Stereophotograph of the skull of cf. Zalambdalestes sp. PSS-MAE 129 in dorsal view, with accompanying line drawing. Part of the endocranial surface of the petrosal is exposed. Gray pattern represents matrix; parallel lines are damaged surfaces. Abbreviations: fr, frontal; mx, maxilla; na, nasal; pe, petrosal; pmx, premaxilla. The meaning of this canal through the lacrimal is uncertain, as no such structure exists among other mammals (Gregory, 1920; Muller, 1934; personal obs.). Some elephant shrews (e.g., Macroscelides proboscidens CM 40789) have a small foramen into the facial process of the lacrimal that must serve a nutritive function, because it has no orbital aperture. In extant placentals, a variety of nerves and vessels cross the orbital rim to reach the face (Sisson, 1910; Greene, 1963; Evans, 1993). The only ones to be enclosed in bone in some forms are the frontal nerves and vessels, but this is invariably in the frontal bone (Sisson, 1910; Williams et al., 1989). Rather than the frontal bone, these nerves and vessels may have been enclosed in the lacrimal in Zalambdalestes. Interestingly, the frontal bone and postorbital process (see below) are situated fairly close to the facial aperture of this canal in PSS-MAE 108 (fig. 18) and 135 (fig. 20). For descriptive purposes, we coin the term ‘‘translacrimal canal’’ for the structure in Zalambdalestes. After our discovery of the translacrimal canal in Zalambdalestes, Archibald and Averianov (2003) reported a very similar structure for Kulbeckia (fig. 51C). The only significant difference between the two is that the passageway in Kulbeckia is much nearer the
2004 WIBLE ET AL.: ZALAMBDALESTES 49 Fig. 21. Continued. probable suture with the jugal and is therefore farther removed from the postorbital process of the frontal. The maxilla in PSS-MAE 108 (fig. 24), 130 (fig. 27), and 135 is limited to the anteroventral part of the orbit and shows appreciable inflation over the crypt that houses the cheekteeth. In PSS-MAE 130, the tips of the left molar roots are exposed and project into the orbit dorsal to the maxilla (fig. 27); the specimen’s right side has not been cleared of matrix in this area. It is likely that the molar roots were visible during life in PSS-MAE 130, with the apertures transmitting alveolar nerves, but the current exposure is chiefly the result of postmortem dorsoventral crushing. Kielan-Jaworowska (1984a: 113) noted ‘‘numerous foramina alveolaria posteriora, in which fragments of molar roots are visible’’ in Zalambdalestes. A few such small foramina are present in the maxilla of PSS-MAE 135, but the molar roots are not exposed. At the anterior apex of the orbit, as stated above, the maxilla forms the floor and the lacrimal the roof of the maxillary foramen, the large posterior opening into the infraorbital canal. Based on the left side of PSS-MAE 108, the medial aspect of this aperture is formed by a third element, which in fact appears to form the bulk of the anterior and medial wall of the orbit (fig. 24). We identify this element as the frontal (see below). Extending posteriorly from the maxillary foramen is an elongate trough in the orbital wall, preserved on the left side of PSS- MAE 108 (fig. 24) and on the right side of PSS-MAE 135. The swollen maxilla forms the ventral aspect of this trough, but the bulk of this feature is within the element described above as the frontal. Kielan-Jaworowska (1984a) identified this element as palatine based on ZPAL MgM-I/14, but PSS-MAE 108 (fig. 24) and 135 have no preserved sutures that delimit this from what is clearly frontal more dorsally in the orbit. At the posterior terminus of this trough is a large aperture in PSS-MAE 108 (fig. 24), in the same position as the small opening in ZPAL MgM-I/14 that Kielan-Jaworowska (1984a) identified as the sphenopalatine foramen. We agree, but note that the aperture in PSS-MAE 108 differs in that it is elongated (fig. 24) and partially divided into a smaller, more anteriorly directed anteroventral foramen and a larger, more medially directed posterodorsal foramen, which we think transmitted the major palatine nerves and vessels to the palate and the caudal nasal nerves and vessels to the nasal cavity, respectively. The dog, for example, has two separate foramina, which are termed the caudal palatine and sphenopalatine foramina (Evans, 1993). Forming the anteroventral border of the foramen transmitting the major palatine nerves and vessels in PSS-MAE 108 is the maxilla (fig. 24). The palatine completes the ventral border of that foramen as well as that for the caudal nasal nerves and vessels. The frontal appears to be the only other element contributing to the borders of the two foramina (see
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zalambdalestes - American Museum of Natural History

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