For years, the oldest turtle fossils we could find had fully formed shells. Now, more primitive fossils are revealing the strange tale of how turtle shells evolved
29 April 2020
CONSIDER the floating fortress that is a sea turtle. It seems to fly gracefully through the water even though it is encased in heavy armour. This combination of poise and protection evolved like any wonder of the animal kingdom, yet until recently the fossils we had found made it seem as if they emerged fully formed hundreds of millions of years ago. In fact, scientists who study the evolution of these animals have a running joke: turtles might as well have come from space.
In the past few years, however, truly ancient fossils have been discovered and they are helping to unravel this real-life just-so story. As we uncover fresh clues, we are learning that the tale of how the turtle got its shell reads nothing like we had previously guessed.
In the UK, the word “turtle” usually refers to the reptiles that swim in the sea, but these are just one branch of a larger group that includes species that burrow in desert sand and slog through swamps. Whether we are talking about a Galapagos tortoise, green sea turtle or red-eared terrapin at the pet shop, they all belong to an order called Testudines – which zoologists tend to call the turtles or chelonians.
All living animals in this order are united by their shell and the modifications required to live inside this box of bone. Their upper ribs are fused to the inside of their shell and their shoulder joints are set inside their ribs. This anatomical form is …