How The Turtle Got Its Shell
A 240-million-year-old fossil was an early proto-turtle
Dr. Hans Sues, the Curator of Vertebrate Paleontology at the Smithsonian's National Museum of Natural History in Washington, studied the fossils and described evidence of shell formation. The trunk ribs are expanded and have started to fuse together into one bone mass. This would eventually become the top shell. Similarly, the bones of a rib-like structure on the underside - or belly shell - are also starting to join together.
The fossils also support the idea that turtles are more closely related to lizards than to dinosaurs and birds.