Document Detail

Anatomical evidence for low frequency sensitivity in an archaeocete whale: comparison of the inner ear of Zygorhiza kochii with that of crown Mysticeti.
MedLine Citation:
PMID:  25400023     Owner:  NLM     Status:  Publisher    
The evolution of hearing in cetaceans is a matter of current interest given that odontocetes (toothed whales) are sensitive to high frequency sounds and mysticetes (baleen whales) are sensitive to low and potentially infrasonic noises. Earlier diverging stem cetaceans (archaeocetes) were hypothesized to have had either low or high frequency sensitivity. Through CT scanning, the morphology of the bony labyrinth of the basilosaurid archaeocete Zygorhiza kochii is described and compared to novel information from the inner ears of mysticetes, which are less known than the inner ears of odontocetes. Further comparisons are made with published information for other cetaceans. The anatomy of the cochlea of Zygorhiza is in line with mysticetes and supports the hypothesis that Zygorhiza was sensitive to low frequency noises. Morphological features that support the low frequency hypothesis and are shared by Zygorhiza and mysticetes include a long cochlear canal with a high number of turns, steeply graded curvature of the cochlear spiral in which the apical turn is coiled tighter than the basal turn, thin walls separating successive turns that overlap in vestibular view, and reduction of the secondary bony lamina. Additional morphology of the vestibular system indicates that Zygorhiza was more sensitive to head rotations than extant mysticetes are, which likely indicates higher agility in the ancestral taxon.
Eric G Ekdale; Rachel A Racicot
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2014-11-14
Journal Detail:
Title:  Journal of anatomy     Volume:  -     ISSN:  1469-7580     ISO Abbreviation:  J. Anat.     Publication Date:  2014 Nov 
Date Detail:
Created Date:  2014-11-17     Completed Date:  -     Revised Date:  2014-11-18    
Medline Journal Info:
Nlm Unique ID:  0137162     Medline TA:  J Anat     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
© 2014 Anatomical Society.
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