Show Details

Turtle Shell Evolution

June 10, 2013

A 260 million-year-old fossil could be the ancestor of turtles.



Filling a gap in turtle evolution. I’m Bob Hirshon and this is Science Update.

There’s no mistaking a turtle for anything else in the animal kingdom. Scientists have long puzzled over the origins of their unique shell. Now, a detailed analysis has revealed that a 260 million-year-old fossil creature called eunotosaurus may be a missing link in turtle evolution. Smithsonian Institution paleontologist Tyler Lyson led the study.

TYLER LYSON (Smithsonian Institution):

So it kind of bridges the morphological gap between a generalized animal, think of like a lizard or something like that, to the highly modified body plan of a turtle. It had part of a shell, but it didn’t have the fully formed shell that we see today.


Lyson says turtle shells are formed from broadened rib bones that fuse with the spine. Eunotosaurus had the same number of broadened ribs, which may have provided them some measure of protection from predators. I’m Bob Hirshon, for AAAS, the science society.

Watch an animated video of turtle evolution

An Eunotosaurus fossil, showing broadened rib bones. (Tyler Lyson)

Read more about this study here: