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Directional hearing in alligators and other archosaurs (dinosaurs) (free pdf)

From: Ben Creisler

A new paper in open access:

Hilary S. Bierman, Jennifer L. Thornton, Heath G. Jones, Kanthaiah
Koka, Bruce A. Young, Christian Brandt, Jakob Christensen-Dalsgaard,
Catherine E. Carr and Daniel J. Tollin (2014)
Biophysics of directional hearing in the American alligator (Alligator
Journal of Experimental Biology 217: 1094-1107
doi: 10.1242/jeb.092866

Physiological and anatomical studies have suggested that alligators
have unique adaptations for spatial hearing. Sound localization cues
are primarily generated by the filtering of sound waves by the head.
Different vertebrate lineages have evolved external and/or internal
anatomical adaptations to enhance these cues, such as pinnae and
interaural canals. It has been hypothesized that in alligators,
directionality may be enhanced via the acoustic coupling of middle ear
cavities, resulting in a pressure difference receiver (PDR) mechanism.
The experiments reported here support a role for a PDR mechanism in
alligator sound localization by demonstrating that (1) acoustic space
cues generated by the external morphology of the animal are not
sufficient to generate location cues that match physiological
sensitivity, (2) continuous pathways between the middle ears are
present to provide an anatomical basis for coupling, (3) the auditory
brainstem response shows some directionality, and (4) eardrum movement
is directionally sensitive. Together, these data support the role of a
PDR mechanism in crocodilians and further suggest this mechanism is a
shared archosaur trait, most likely found also in the extinct

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