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Fossorial Origin of the Turtle Shell.

Tyler R Lyson1, Bruce S Rubidge2, Torsten M Scheyer3

  • 1Department of Earth Sciences, Denver Museum of Nature and Science, Denver, CO 80205, USA; Evolutionary Studies Institute, University of the Witwatersrand, PO Box Wits, 2050 Johannesburg, South Africa.

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The evolution of the turtle shell began with broadened ribs, initially for digging (fossoriality), not protection. This adaptation in early turtles like Eunotosaurus influenced their body plan and survival.

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Area of Science:

  • Paleontology
  • Evolutionary Biology
  • Comparative Anatomy

Background:

  • The turtle shell, a defining feature, evolved from broadened ribs, which initially incurred locomotion and respiratory costs.
  • Fossil and developmental data suggest rib broadening preceded the complete shell structure.

Purpose of the Study:

  • To investigate the initial evolutionary drivers behind rib broadening in turtles.
  • To analyze fossil evidence of early turtle ancestors and their ecological adaptations.

Main Methods:

  • Analysis of new fossil material of Eunotosaurus africanus.
  • Comparative skeletal analysis of Eunotosaurus with extant and fossil turtles.
  • Identification of fossorial (digging) adaptations within the Eunotosaurus skeleton.

Main Results:

  • Eunotosaurus africanus fossils indicate rib broadening was an adaptation for fossoriality, providing a stable base for digging.
  • Numerous fossorial features in Eunotosaurus suggest a digging-influenced body plan in the common ancestor of turtles.
  • These adaptations may have aided early turtles in moving to aquatic environments and surviving the Permian/Triassic extinction.

Conclusions:

  • The turtle shell's origin is linked to fossorial adaptations, not initially for defense.
  • Early turtle evolution was significantly shaped by digging behaviors.
  • Fossoriality may have been crucial for turtle survival during major extinction events.