Predicting ecology and hearing sensitivities in Parapontoporia-An extinct long-snouted dolphin.

Abstract

Analyses of the cetacean (whale and dolphin) inner ear provide glimpses into the ecology and evolution of extinct and extant groups. The paleoecology of the long-snouted odontocete (toothed whale) group, Parapontoporia, is primarily marine with its depositional context also suggesting freshwater tolerance. As an extinct relative of the exclusively riverine Lipotes vexillifer, Parapontoporia provides insight into a transition from marine to freshwater environments. High-resolution X-ray CT scans (~3 microns or less) of three individual specimens from two species, P. sternbergi and P. pacifica, were acquired. Digital endocasts of the inner ear labyrinths were extracted non-destructively. Nine measurements of the inner ear were compared with an existing dataset covering 125 terrestrial and aquatic artiodactyls. These measurements were then subjected to a principal component analysis to interpret hearing sensitivities among other artiodactyls. Based on our analyses, Parapontoporia was likely to have been able to hear within narrow-band high frequency (NBHF) ranges. This finding indicates another convergence of NBHF-style hearing, or, more intriguingly, suggests that it may be an ancestral characteristic present among the longirostrine dolphins that dominated in the Miocene prior to the evolution of more modern lineages.