Geogale aurita, Milne-Edwards & A. Grandidier, 1872

ASHER, ROBERT J., 2001, Cranial Anatomy in Tenrecid Insectivorans: Character Evolution Across Competing Phylogenies, American Museum Novitates 3352, pp. 1-55 : 33-35

Geogale aurita (MCZ 45499; fig. 28)

The vomeronasal organ of Geogale is small compared to that of Potamogale . Its anteriormost point is directly over the posterior margin of the palatine papilla. Instead of traversing a large portion of the nasal floor as in Potamogale , the vomeronasal organ tapers to a posterior terminus at about the same transverse plane as the third upper incisor— roughly 1 mm posterior to its starting point. In the postnatal MCZ 45499, it comprises about 10% of nasal capsule length (about 10 mm) and 8% of head length (14 mm). Proportions are similar in the larger ZIUT individual (SVL 43 mm): the 1.2­mm vomeronasal organ comprises 9% of nasal capsule length (14.3 mm) and 6% of head length (21 mm).

The vomeronasal organ itself is kidneyshaped and laterally concave. Blood vessels are conspicuous dorsolateral and ventromedial to the vomeronasal organ. The paraseptal cartilages are most evident ventral to the vomeronasal organ along its length and are reduced medially. Relative to other animals examined here, there is very little space between the vomeronasal organ on each side of the septum. In other taxa, a dorsally extending flange of the paraseptal cartilage contributes to the space separating each half of the paired vomeronasal organ, whereas in Geogale bony elements of the nasal septum are evident medial to the vomeronasal organ (compare figs. 24 and 29 or slices 14.2.4 of Potamogale and 8.5.5 of Geogale ). This may be due to the advanced ontogenetic stage and consequent resorption of cartilage in the available Geogale specimens.

At the anterior margin of the vomeronasal organ of Geogale , just dorsal to the nasopal­ atine duct, a small outer bar connects the ventrolateral and ventromedial components of the paraseptal cartilage, lying dorsal to the vomeronasal duct (e.g., slice 8.1.5; figs. 28, 29).

Posterior to the anterior margin of the first upper incisors and continuing through the length of the premaxilla, the cartilaginous nasal septum consists of a single anteroposteriorly running cylinder, surrounded by ossifications of the premaxilla (slice 11.2.3). In this region the septum lacks a connection to the nasal roof. This condition may simply be a result of resorption of cartilage in a relatively well­ossified postnatal individual, an interpretation supported by the observation that other adult specimens (e.g., IZEA 939 and AIG 1227 Micropotamogale and ZIUT Sorex ) also lack a cartilaginous septum­roof connection in parts of the nasal fossa.

At its anterior margin, the vomeronasal organ gives off a well­defined vomeronasal duct (slice 8.2.3; fig. 29), which enters the nasopalatine canal dorsally as the latter opens into the nasal fossa proper. As in most other taxa described here, the nasopalatine canal is paired, opening on either side of a well­defined palatine papilla (slice 7.5.5). A very small nasopalatine duct cartilage is evident along the lateral margin of the incisive foramina (slice 8.5.1), which shows no connection to other nasal cartilages.

Within the palatine papilla is a cartilaginous body (slice 8.1.4; fig. 29), ending anteriorly in two points. Although ubiquitous among marsupials (Sánchez­Villagra, 2001), this papillary cartilage has been observed in relatively few placental taxa, such as Elephantulus and Tupaia (Wöhrmann­Repenning, 1984, 1987).

Just anterior to the rostral openings of the vomeronasal ducts is the inferior septal ridge, a laterally projecting flap of epithelial tissue, closely associated with the posterior margin of the anterior transverse lamina (slice 7.2.4). This structure extends ventrolaterally out from the posterior tip of the medial arm of the anterior transverse lamina, and supports both glandular and olfactory tissue.

The lack of prominent medial processes of the paraseptal cartilage contributes to the absence of a connection between it and the anterior transverse lamina. That is, the nasal cavity floor anterior to the vomeronasal duct is not broadly continuous with the paraseptal cartilage.

Geogale also displays a complete zona annularis, that is, continuity between the nasal septum, anterior transverse lamina, and nasal sidewall for a short distance immediately an­ terior to the first upper incisor (e.g., slice 4.4.3).

Geogale exhibits relatively large superior alar processes, located just posterior to the external nares, that serve as the site of origin of several facial muscles (e.g., slice 3.4.4). The alar processes are broadly connected to the nasal floor ventrally and show a narrow alicupular commissure anteriorly.