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Evaluation of Planar-Cell-Polarity Phenotypes in Ciliopathy Mouse Mutant Cochlea

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Evolutionary paths to mammalian cochleae.

Geoffrey A Manley¹

¹Cochlear and Auditory Brainstem Physiology, IBU, Faculty V, Carl von Ossietzky University Oldenburg, Carl von Ossietzky Strasse 9-11, 26129 Oldenburg, Germany. geoffrey.manley@uni-oldenburg.de

Journal of the Association for Research in Otolaryngology : JARO

|September 18, 2012

Summary

This summary is machine-generated.

Mammalian high-frequency hearing evolved gradually, with a fully coiled cochlea appearing around 125 million years ago. Ultrasonic hearing developed even later, with modern bat cochleae showing specialized features much more recently.

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Area of Science:

Paleontology
Evolutionary Biology
Auditory Neuroscience

Background:

Mammalian evolution traces back over 200 million years, with distinct lineages developing unique auditory structures.
Early mammals possessed three middle ear ossicles, but these were not initially freely suspended as in modern mammals.
Cochlear length and coiling varied significantly across mammalian lineages and geological time.

Purpose of the Study:

To review recent paleontological insights into mammalian cochlear and middle ear evolution.
To determine the evolutionary timeline of high-frequency hearing (>20 kHz) in mammals.
To understand the development of ultrasonic hearing capabilities.

Main Methods:

Review of paleontological data, particularly from micro-CT scans of fossil mammals.
Comparative analysis of cochlear structures across mammalian ancestors and modern species.
Examination of evolutionary timelines for key auditory structures and hearing capabilities.

Main Results:

Early mammalian cochleae were short (approx. 2 mm) and lacked significant coiling, persisting in multituberculates and monotremes.
Cochlear coiling in the therian lineage (placental and marsupial mammals) developed gradually, with a full coil appearing by the Early Cretaceous (~125 Ma).
High-frequency hearing (>20 kHz) likely emerged around the Early Cretaceous, coinciding with the evolution of the fully coiled cochlea in therians. Ultrasonic hearing in bats evolved much later.

Conclusions:

The evolution of the mammalian cochlea and high-frequency hearing was a protracted process, not a single event.
Cochlear coiling and high-frequency sensitivity evolved independently and at different rates across mammalian lineages.
Modern auditory specializations, such as ultrasonic hearing in bats, represent late-stage evolutionary developments built upon earlier foundational structures.