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Processing Embryo, Eggshell, and Fungal Culture for Scanning Electron Microscopy
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Published on: August 16, 2019

Evolutionary origin of the turtle shell.

Tyler R Lyson1, Gabe S Bever, Torsten M Scheyer

  • 1Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT 06511, USA. tyler.lyson@gmail.com

Current Biology : CB
|June 4, 2013
PubMed
Summary
This summary is machine-generated.

The origin of the turtle shell is clarified by studying the Permian reptile Eunotosaurus africanus. Its unique features support a model of early turtle evolution, placing its divergence in the Middle Permian.

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Area of Science:

  • Paleontology
  • Evolutionary Biology
  • Herpetology

Background:

  • The evolutionary origin of the turtle shell has been a long-standing biological puzzle.
  • Previous models synthesized fossil and developmental data, particularly after the discovery of Odontochelys semitestacea.
  • The history of the turtle stem group remains incompletely understood.

Purpose of the Study:

  • To integrate novel data from Eunotosaurus africanus into existing models of turtle shell evolution.
  • To investigate the phylogenetic position of Eunotosaurus africanus as an early stem turtle.
  • To refine the understanding of early turtle evolutionary transformations.

Main Methods:

  • Comparative anatomical analysis of Eunotosaurus africanus fossils.
  • Integration of fossil data with existing phylogenetic and developmental models of turtle evolution.
  • Comparison of Eunotosaurus africanus characters with predicted traits for early turtle ancestors.

Main Results:

  • Eunotosaurus africanus exhibits key features aligning with predicted early turtle evolution, including nine elongate trunk vertebrae and T-shaped ribs.
  • Inferred loss of intercostal muscles and ventral reorganization of respiratory muscles were observed.
  • Subdermal bone outgrowth from rib perichondral collars and simplified paired gastralia were identified.

Conclusions:

  • Eunotosaurus africanus provides strong support for its placement as an early stem turtle.
  • The findings support a model of successive divergences from the turtle stem lineage, including E. africanus, O. semitestacea, and Proganochelys quenstedti.
  • Early turtle evolutionary transformations occurred by the Middle Permian, consistent with molecular divergence estimates and independent of turtle origin within or outside crown Diapsida.