Document Detail

Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water.
MedLine Citation:
PMID:  21873217     Owner:  NLM     Status:  MEDLINE    
Eocene archaeocete whales gave rise to all modern toothed and baleen whales (Odontoceti and Mysticeti) during or near the Eocene-Oligocene transition. Odontocetes have asymmetrical skulls, with asymmetry linked to high-frequency sound production and echolocation. Mysticetes are generally assumed to have symmetrical skulls and lack high-frequency hearing. Here we show that protocetid and basilosaurid archaeocete skulls are distinctly and directionally asymmetrical. Archaeocete asymmetry involves curvature and axial torsion of the cranium, but no telescoping. Cranial asymmetry evolved in Eocene archaeocetes as part of a complex of traits linked to directional hearing (such as pan-bone thinning of the lower jaws, mandibular fat pads, and isolation of the ear region), probably enabling them to hear the higher sonic frequencies of sound-producing fish on which they preyed. Ultrasonic echolocation evolved in Oligocene odontocetes, enabling them to find silent prey. Asymmetry and much of the sonic-frequency range of directional hearing were lost in Oligocene mysticetes during the shift to low-frequency hearing and bulk-straining predation.
Julia M Fahlke; Philip D Gingerich; Robert C Welsh; Aaron R Wood
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2011-08-22
Journal Detail:
Title:  Proceedings of the National Academy of Sciences of the United States of America     Volume:  108     ISSN:  1091-6490     ISO Abbreviation:  Proc. Natl. Acad. Sci. U.S.A.     Publication Date:  2011 Aug 
Date Detail:
Created Date:  2011-08-31     Completed Date:  2011-11-08     Revised Date:  2013-06-27    
Medline Journal Info:
Nlm Unique ID:  7505876     Medline TA:  Proc Natl Acad Sci U S A     Country:  United States    
Other Details:
Languages:  eng     Pagination:  14545-8     Citation Subset:  IM    
Museum of Paleontology, Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
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MeSH Terms
Biological Evolution*
Hearing / physiology*
Skull / anatomy & histology*
Whales / anatomy & histology*,  physiology*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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