The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


Cochlear Labyrinth Volume and Predicted Hearing Abilities in Adapis, Necrolemur, Homunculus, and Tremacebus

ELISSA M. LUDEMAN1, E. CHRISTOPHER KIRK2, ASHLEY D. GOSSELIN-ILDARI3, AUTUMN BLAYLOCK2, RICHARD F. KAY4 and MARC GODINOT5.

1Department of Anthropology, Center for the Study of Human Origins, New York Consortium in Evolutionary Primatology, New York University, 2Department of Anthropology, The University of Texas at Austin, 3Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, 4Department of Evolutionary Anthropology, Duke University, 5Département Histoire de la Terre, Muséum National d’Histoire Naturelle

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Previous analyses of cochlear labyrinth morphology provide evidence of a functional relationship between hearing abilities, cochlear volume, and basilar membrane length. Among therian mammals, cochlear volume is negatively correlated with both the high and low frequency limits of hearing. These functional relationships make it possible to reconstruct attributes of the hearing abilities of extinct taxa based on the anatomy of the cochlear labyrinth. We analyzed the cochlear labyrinths of four fossil primate crania, including two species from the Eocene of Europe (Adapis parisiensis and Necrolemur antiquus) and two species from the Miocene of Patagonia (Homunculus patagonicus and Tremacebus harringtoni). Fossils were CT scanned at a resolution of 20-40 microns and the cochlear portion of the bony labyrinth was segmented using a variant of the half maximum height method. Cochlear volumes of fossil taxa were compared with data for 27 extant species with known audiograms from 8 mammalian orders. High and low frequency limits of hearing at 60db SPL were estimated using phylogenetic generalized least-squares regressions. These methods yield estimated hearing ranges of: Adapis (100Hz -42.0kHz); Necrolemur (100Hz – 65.0kHz); Homunculus (70Hz – 43.0kHz); Tremacebus (70Hz – 43.0kHz). Necrolemur is thus estimated to have exhibited better high frequency hearing than the other fossil taxa in our analysis. These results suggest that Tremacebus and Homunculus had very similar hearing abilities that were comparable to those of some extant platyrrhines (e.g., Saimiri). Similarly, estimated thresholds for Adapis and Necrolemur are comparable to those of some living strepsirrhines (e.g., Perodicticus and Galago senegalensis, respectively).

This project made possible by NSF Grant 0851272 awarded to Richard F. Kay.

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