Morphology of the tympanic‐basicranial region in Mirounga leonina (Phocidae, Carnivora), postnatal ontogeny and sexual dimorphism

Abstract

The auditory region of pinnipeds has seldom been described. Here we describe and analyze the ontogenetic trajectory of the tympanic bulla of the southern elephant seal, Mirounga leonina (Phocidae, Mammalia). This species is extremely sexually dimorphic and highly polygynous (organized in harems). We examined 118 specimens, arranged in three age classes (CI, CII, and CIII), ranging from newborn to adults (males and females). To analyze the overall size and shape of the tympanic bulla we performed a geometric morphometric analysis including 87 skulls. Females reach definitive shape and size of the bulla at earlier ontogenetic stages than males, in agreement with their earlier involvement in reproductive activities. The internal anatomy of the tympanic region (e.g. form and extension of the paries) does not show remarkable differences between sexes or age classes. The greatest differences between age classes are related to bone thickness, resulting from the apposition of new annual layers. An examination of possible sex-related external differences among age classes shows significant shape differences between males and females in CIII. The morphology observed in neonates is conserved across all individuals from CI, which included specimens up to 1 year old. Clear morphological differences were observed between CI individuals, on one hand, and CII individuals plus CIII females on the other. During cranial development of both male and females, the glenoid cavity expands and compresses the bulla; this condition reaches its maximum expression in CIII males. CIII males showed the greatest morphological differences, with respect to both CI and CII individuals, and CIII females.

Anatomical study of the auditory region of Arctotherium tarijense (Ursidae, Tremarctinae), an extinct short‐faced bear from the Pleistocene of South America

“…This process contacts the processus postglenoideus and the processus paraoccipitalis (Figs 1A,D,G and 6B). In the anteroventral part of the medial surface of the pars petrosa, the meatus acusticus internus and the fossa subarcuata open (Loza et al 2015). This fossa housed the paraflocculus of the cerebellum (Wible et al 1995), which is responsible for the control of the amplitude and timing of compensatory eye movements and the vestibulocular reflex (De Zeeuw et al 2004).…”

How flat can a horse be? Exploring 2D approximations of 3D crania in equids

“…Research on anatomical and ecomorphological variation of modern and past representatives of the megafauna, whose partial but rapid extinction on land at the end of the Pleistocene still poses an unresolved dilemma (Koch and Barnosky, 2006), attracts great interest. Indeed, large mammals and birds, but also 'reptiles' such as crocodyles and dinosaurs, have been the subject of innumerable morphological studies, including many 2D GMM analyses (e.g., Pierce et al, 2008;Amaral et al, 2009;Brombin et al, 2009;Figueirido et al, 2009;Brusatte et al, 2012;Christiansen, 2012;Loza et al, 2015;Meloro et al, 2017;Page and Cooper, 2017;Angulo-Bedoya et al, 2019).…”

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

“…; Loza et al. ; Loza, ), all within a descriptive and phylogenetic framework. Today the Carnivora are split into three main clades, Arctoidea, Aeluroidea, and Cynoidea, partially on the basis of auditory features such as the presence or absence of the septum bullae (Hough, ; Ivanoff, ).…”