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Dissection of the Auditory Bulla in Postnatal Mice: Isolation of the Middle Ear Bones and Histological Analysis
Published on: January 4, 2017
Middle ear cavity morphology is consistent with an aquatic origin for testudines.
Katie L Willis1, Jakob Christensen-Dalsgaard, Darlene R Ketten
1Department of Biology, University of Maryland, College Park, Maryland, United States of America. kwillis@umd.edu
Plos One
|January 24, 2013
Summary
Turtles evolved to hear underwater, with their middle ear cavities resonating in aquatic sound fields. This finding supports an aquatic origin for testudines and their underwater sound detection capabilities.
Area of Science:
- Vertebrate Phylogeny
- Paleontology
- Bioacoustics
Background:
- Phylogenetic placement of turtles (testudines) is debated due to conflicting morphological and molecular data.
- The ecological niche of early turtles remains unclear, impacting our understanding of their evolutionary adaptations.
- Investigating turtle hearing adaptations can shed light on their evolutionary history and environmental interactions.
Purpose of the Study:
- To examine middle ear morphology and scaling in turtles to understand hearing evolution in different environments.
- To test the hypothesis of an aquatic origin for turtles using middle ear cavity analysis.
- To determine the functional role of the middle ear cavity in underwater sound detection.
Main Methods:
- Utilized 3D reconstructions from micro magnetic resonance (MR) and submillimeter computed tomography (CT) scans.
- Analyzed middle ear morphology and scaling across extant and extinct turtle families.
- Modeled middle ear cavities as air-filled spheres to calculate underwater sound resonance.
Main Results:
- All turtle families share a similar bony middle ear cavity shape, with the tympanic disk on the rostrolateral edge.
- Sea turtles exhibit varying degrees of soft tissue filling the middle ear cavity.
- Calculated resonances for middle ear cavity volumes largely fell within known turtle hearing ranges for underwater sound.
- No significant differences in middle ear cavity volume scaling with head size were found across phylogenetic and ecological groups.
Conclusions:
- The middle ear cavity's predicted underwater resonance supports an aquatic origin for turtles.
- The middle ear morphology is functionally adapted for underwater sound detection.
- This study provides evidence for the role of hearing in turtle evolutionary history and adaptation to aquatic environments.
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