Document Detail

Evolutionary paths to mammalian cochleae.
MedLine Citation:
PMID:  22983571     Owner:  NLM     Status:  MEDLINE    
Evolution of the cochlea and high-frequency hearing (>20 kHz; ultrasonic to humans) in mammals has been a subject of research for many years. Recent advances in paleontological techniques, especially the use of micro-CT scans, now provide important new insights that are here reviewed. True mammals arose more than 200 million years (Ma) ago. Of these, three lineages survived into recent geological times. These animals uniquely developed three middle ear ossicles, but these ossicles were not initially freely suspended as in modern mammals. The earliest mammalian cochleae were only about 2 mm long and contained a lagena macula. In the multituberculate and monotreme mammalian lineages, the cochlea remained relatively short and did not coil, even in modern representatives. In the lineage leading to modern therians (placental and marsupial mammals), cochlear coiling did develop, but only after a period of at least 60 Ma. Even Late Jurassic mammals show only a 270 ° cochlear coil and a cochlear canal length of merely 3 mm. Comparisons of modern organisms, mammalian ancestors, and the state of the middle ear strongly suggest that high-frequency hearing (>20 kHz) was not realized until the early Cretaceous (~125 Ma). At that time, therian mammals arose and possessed a fully coiled cochlea. The evolution of modern features of the middle ear and cochlea in the many later lineages of therians was, however, a mosaic and different features arose at different times. In parallel with cochlear structural evolution, prestins in therian mammals evolved into effective components of a new motor system. Ultrasonic hearing developed quite late-the earliest bat cochleae (~60 Ma) did not show features characteristic of those of modern bats that are sensitive to high ultrasonic frequencies.
Geoffrey A Manley
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Review     Date:  2012-09-15
Journal Detail:
Title:  Journal of the Association for Research in Otolaryngology : JARO     Volume:  13     ISSN:  1438-7573     ISO Abbreviation:  J. Assoc. Res. Otolaryngol.     Publication Date:  2012 Dec 
Date Detail:
Created Date:  2012-11-26     Completed Date:  2013-07-22     Revised Date:  2013-12-04    
Medline Journal Info:
Nlm Unique ID:  100892857     Medline TA:  J Assoc Res Otolaryngol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  733-43     Citation Subset:  IM    
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MeSH Terms
Anion Transport Proteins / physiology
Biological Evolution*
Cochlea / anatomy & histology*,  physiology
Reg. No./Substance:
0/Anion Transport Proteins; 0/SLC26A5 protein, human

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