PREDICTING ECOLOGY AND HEARING SENSITIVITIES IN PARAPONTOPORIA (Invited Presentation)

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 odontocete (toothed whale) group, Parapontoporia, is primarily marine with depositional context also suggesting freshwater tolerance. As an extinct relative of the exclusively riverine Lipotes vexillifer, Parpontoporia 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 using the software VGStudioMax v. 3.5.2. Nine measurements of the cochlea including secondary bony lamina length, semicircular canal length, height, width, and fenestra cochleae surface area were added to an existing dataset covering 103 terrestrial and aquatic artiodactyls. These measurements were then subjected to a Principal Component Analysis (PCA) to interpret hearing sensitivities among other artiodactyls. From an analysis of the specimens, Parapontoporia was not likely to have been a narrow-band high frequency (NBHF) echolocator, and differences in cochlear length demonstrate intraspecific and interspecific variation. The semicircular canals were measured for comparison with previous work, highlighting a longer lateral canal, as expected compared with other odontocetes. Studying the inner ear of Parapontoporia will help inform on the ‘river dolphin’ transitions from marine to riverine environments.