It’s a question so obvious a schoolchild can ask it, but for more than a century, consensus has eluded the paleontologists and evolutionary biologists who study the reptiles and their bony carapaces. Now, a group of scientists at Yale University and the Smithsonian Institution argue that a reptile fossil that’s been gathering dust in museum collections is actually a turtle ancestor, and that its reduced number of ribs, distribution of muscles, and T-shaped ribs could help settle the question once and for all.

In a new paper published Thursday in the journal Current Biology, they unveil the argument that a 260 million-year-old creature called Eunotosaurus africanus was a turtle ancestor, hoping to help resolve a debate that has split the scientific community for decades.