Sensory Anatomy and Sensory Ecology of Vintana Sertichi (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar

Abstract

ABSTRACT—Living mammals are distinguished from other extant tetrapods by adaptations for improved senses of hearing, touch, and smell. These adaptations, and concomitant reductions in visual anatomy, evolved during the Mesozoic in the mammalian and therian stem lineages. Here, we present a comparative study of the sensory anatomy of the Late Cretaceous gondwanatherian mammaliaform Vintana sertichi in order to draw inferences regarding its sensory abilities and sensory ecology. Our analyses demonstrate that Vintana has relatively large orbits that may have accommodated large eyes. Vintana also possessed cochlear primary and secondary osseous laminae and a cochlear canal that was relatively longer than in non-mammaliaform cynodonts but shorter than in extant therians. These features suggest that Vintana had some capacity for high-frequency hearing (i.e., >20 kHz), but that its cochlea may have encoded a more limited range of frequencies than the cochleas of most extant therians. The semicircular canals of Vintana have large radii of curvature and are nearly orthogonal, suggesting high sensitivity to angular head accelerations. These vestibular features may have evolved in order to stabilize large eyes during rapid and/or agile locomotion. Combined with evidence for large olfactory bulbs and a large trigeminal endocast, these data reveal that Vintana possessed a unique suite of sensory adaptations that distinguish it from other Mesozoic mammaliaforms. If these inferences are correct, then Vintana was probably a large-eyed and agile species, with a keen sense of smell and better high-frequency hearing than most other Mesozoic mammaliaforms.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

ACKNOWLEDGMENTS

R. Kay and M. Cartmill are due special thanks from E.C.K. for many years of insightful discussions of sensory anatomy and comparative methods. A. Latimer and R. Simon provided helpful discussions of monotreme anatomy and physiology. M. Muchlinski kindly assisted in preparing her infraorbital canal data for analysis, and M. Stewart assisted with data entry. T. Rowe generously shared μCT scans of monotremes. R. David and M. Silcox provided useful comments for the revision of this paper. This research was supported by grants from the National Geographic Society (8597-09) and the National Science Foundation (EAR-0446488, EAR-1123642).