Turtle Ancestors -- Fossil Discovery Leads to a New Theory

[Recusant]

An eight year old boy found a turtle fossil that has resulted in a new theory about the evolution of turtle's shells.

"Real reason turtles have shells: Burrowing tool" | ScienceDaily

An artist's rendering of the proto-turtle Eunotosaurus (foreground) digging into the ground as a herd of Bradysaurus wander across the south African landscape nearby. Image credit: Audrey Atuchin

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 by an international group of paleontologists suggests that the broad ribbed proto shell on the earliest partially shelled fossil turtles was initially an adaptation, for burrowing underground, not for protection. Paleontologist Tyler Lyson from the Denver Museum of Nature & Science is among the scientists that helped make this discovery.

"Why the turtle shell evolved is a very Dr. Seuss-like question and the answer seems pretty obvious -- it was for protection," said Dr. Lyson, lead author of Fossorial Origin of the Turtle Shell, which was released today by Current Biology. But just like the bird feather did not initially evolve for flight, the earliest beginnings of the turtle shell was not for protection but rather for digging underground to escape the harsh South African environment where these early proto turtles lived."

[Continues . . .]

There's a pop-science article about this that gives more details about why Lyson et al. came up with this idea.

"Turtles Evolved Shells To Help Them Dig, Not For Protection" | IFLScience

The Karoo Basin of South Africa was a harsh, arid place back in the Permian, bathed in heat and full of fearsome predators, including the large, carnivorous Gorgonopsia. Quickly digging into the ground was one way to avoid the hazardous world at the surface, and ancestral turtles like E. africanus began to evolve adaptations to this over a relatively short space of time.

Not only did their legs gradually reposition themselves, but their rib cages significantly broadened to make them flatter overall. Ultimately, this gave them a more mechanically stable platform from which to operate their digging forelimbs, even if it restricted their breathing efficiency and slowed their pace down. Better diggers produced more survivors compared to their surface-dwelling counterparts.

[Continues . . .]