National History Museum
 
 

Why did the turtle shell evolve?

Reconstruction of burrowing Eunotosaurus africanus, in the Karoo Basin

It is common knowledge that the modern turtle shell is largely used for protection. No other living vertebrate has so drastically altered its body to form such an impenetrable protective structure as the turtle. However, a new study published in Current Biology on the earliest partially shelled fossil turtles suggests the broad ribbed proto shell was initially an adaptation, not for protection, but rather for burrowing underground.

The early evolution of the turtle shell has long puzzled scientists. “We knew from both the fossil record and observing how the turtle shell develops in modern turtles that one of the first major changes towards a shell was the broadening of the ribs,” says lead author Dr. Lyson of the Denver Museum of Nature and Science.

“From the bone microstructure, we found additional evidence of increased muscle power in the forelimbs, a strong indication that this animal was a regular digger” says co-author Dr Jennifer Botha-Brink from the National Museum, Bloemfontein who was involved in the bone microstructure analysis.

A big breakthrough came with the discovery of several specimens of the oldest (260 million years old) partially shelled proto turtle, Eunotosaurus africanus, from the Karoo Basin of South Africa. Several of these specimens were discovered by two of the studies’ co-authors, Drs. Roger Smith and Bruce Rubidge from the University of the Witwatersrand in Johannesburg, but the most important specimen in the study was found by a then eight year old South African boy, Kobus Snyman, on his father’s farm in the Western Cape of South Africa.

“As is the case with many evolutionary innovations, the turtle shell developed for entirely different reasons from its function today. In this instance, the broadened ribs, originally adapted for keeping the body stable during digging and providing a foundation for the insertion of powerful shoulder and arm muscles, only became involved in protection millions of years later”, says Dr. Jennifer Botha-Brink.

The study includes authors from the United States, South Africa, and Switzerland.

 

Contact:

Dr Jennifer Botha-Brink

National Museum, Bloemfontein

Email: jbotha [at] nasmus [dot] co [dot] za

Phone: +27 51 447 9609

 

Author Institutions’ Media Contacts:

University of Witswatersrand

Erna van Wyk: erna [dot] vanwyk [at] wits [dot] ac [dot] za

Shirona Patel: Shirona [dot] Patel [at] wits [dot] ac [dot] za