The tympanic region of Otaria byronia (Otariidae, Carnivora), morphology, ontogeny, age classes and dimorphism

LOZA CM; SCARANO AC; GALLIARI FC; SOIBELZON LH; NEGRETE J; CARLINI AA

JOURNAL OF ANATOMY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2017

0021-8782

ABSTRACT23 Here we describe and explore for the first time the ontogeny and sexual24 dimorphism of the auditory region of Otaria byronia. We studied skulls and25 tympanic-basicranial region of 237 specimens of different ages and sexes.26 Geometric morphometric methods were used to analyze the tympanic bulla.27 In addition, 3D reconstructions of the tympanic bulla were performed using28 Computed Tomography Analysis Scans, and a serial wearing technique. We29 provide a description of the external and internal morphology of the tympanic30 bulla in both sexes and across different stages (bioclasses). The average31 shape of the bulla in O. byronia has a subtriangular contour, with variations32 between sexes and ages. Each stage (bioclasses I, II, and III) is33 characterized by the respective mean shape of the tympanic bulla and34 designated as a morphoclass (I, II, and III). In all cases, the ectotympanic35 shows greater surface area than the endotympanic, as in other otariids, and36 contrasting with Phocidae. Along ontogeny the relative size of the37 ectotympanic becomes greater, growing in all directions and covering the38 endotympanic. This pattern is verified to greatest extent in adult males, in39 which the ectotympanic forms an extremely well developed apophysis40 jugulare. No differences in internal morphology were recorded between ages41 and sexes. The bulla does not increase in thickness in successive age42 classes; in fact, the walls are extremely thin in the adult stages, despite the43 great development of its processes. This pattern is opposite to that observed44 in Phocidae. In morphoclass-III, adult males older than seven years undergo45 hypermorphic change that results in a peramorphic condition when compared46 to adult females. These changes probably follow the same pattern shown byJournal of Anatomy Page 2 of 6647 the rest of the skull and contribute to the marked sexual dimorphism of the48 species.