ANTILOPINAE, Gray, 1821

Farke, Andrew A., 2010, Evolution and functional morphology of the frontal sinuses in Bovidae (Mammalia: Artiodactyla), and implications for the evolution of cranial pneumaticity, Zoological Journal of the Linnean Society 159 (4), pp. 988-1014 : 998-999

ANTILOPINAE

The morphology of the sinus is quite variable within this clade, ranging from absent to extensive, so the sinuses are described by species or by groups of species.

Antidorcas marsupialis

This species has the largest and most extensive frontal sinuses of any antilopine, extending into the base of the horncores and to the very edge of the orbital margin ( Fig. 4C, D ). The supraorbital strut displays the typical bovid condition, extending from the caudal edge of the supraorbital canal and then trending caudomedially. It terminates on the wall of the midline strut just rostral to the base of the horn and its associated cornual diverticulum. Other struts are relatively widely spaced. The frontal sinus in this species is contained completely within the frontal bone.

Antilope cervicapra , Eudorcas thomsonii , Gazella subgutturosa , Litocranius walleri , Madoqua kirkii , Nanger granti , and Saiga tatarica

The frontal sinuses in these taxa are relatively small and restricted rostrally, terminating rostral to the supraorbital canal in most cases ( Fig. 3A, B ). In Saiga tatarica , and one specimen of E. thomsonii (YPM 11526), the sinus extended up to the lateral portion of the supraorbital canal, within the supraorbital pits. Regardless, the canal is never surrounded completely by the sinuses, as seen in some other bovids (e.g. Alcelaphus buselaphus ). The sinus on each side is restricted to the lateral portion of the frontal bone and separated from the lacrimal sinus by a thin lamina of bone. In nearly all individuals examined of these species, the sinus was completely unstrutted. The only exceptions were specimens of Antilope cervicapra (AMNH 54486) and Nanger granti (YPM 11526; Fig. 3B ), which displayed a single strut at the middle of each sinus. In one specimen each of L. walleri (AMNH 81170) and Nanger granti (YPM 9480), only one of the two sinuses was strutted. One specimen of M. kirkii (YPM 9600) exhibited strong asymmetry in the shape and extent of the frontal sinuses. The left frontal sinus was quite well developed, extending to the lateral portion of the supraorbital canal, whereas the right frontal sinus was poorly developed, and terminated rostral to its ipsilateral supraorbital canal. Similar, although less extreme, asymmetry in the frontal sinuses was observed in the other M. kirkii specimens, and in two specimens of Nanger granti (YPM 9480 and 9605).

Other antelopines

Ourebia ourebi lacks frontal sinuses as well as a distinct frontal recess on the internal surface of the frontal bone. Gazella dorcas , Procapra gutturosa , and Raphicerus campestris ( Fig. 3E–G ) also lack frontal sinuses, but do have a distinct frontal recess in nearly all cases (although no distinct recess was observed in the Procapra gutturosa specimen AMNH 85235). In some specimens the recess arguably borders on a true sinus in its degree of depression into the ventral surface of the frontal.

Figures

Figure 3. Digital reconstructions and computed tomography (CT) slices of bovid skulls, illustrating the frontal sinuses and related anatomy, in Nanger granti (A–C; YPM 11526), Cephalophus leucogaster (D, F; AMNH 52802), and Raphicerus campestris (E, G; YPM 10276). In C, note the distinct frontal sinus that invades the trabecular bone, is bounded by cortical bone on all sides, and is distinctly separated from the olfactory turbinals below. This contrasts with the condition in E, in which a distinct recess above the olfactory turbinals is pressed into the frontal bone, but does not actually invade the trabecular bone. In D, no recess exists at all, and the space beneath the frontals is entirely occupied by turbinals. The dashed lines in A, F, and G indicate the approximate positions of the coronal CT slices in C, D, and E, respectively. The boxed areas in A and B indicate the region of the skull that has been rendered partially transparent in order to visualize the anatomy of the frontal sinuses. Scale bars: 5 cm.

Figure 4. Digital reconstructions from computed tomography (CT) scan data of the skulls of Damaliscus lunatus (A–B; YPM 9586) and Antidorcas marsupialis (C–D; AMNH 233055), illustrating the frontal sinuses and related anatomy. Skulls are shown in lateral (A, C) and dorsal (B, D) views. The boxed areas indicate the region of the skull that has been rendered partially transparent in order to visualize the anatomy of the frontal sinuses. The horns have been truncated in C and D. Scale bars: 5 cm.