Scientists say a 260-million-year-old fossil from Africa is that of the earliest-known turtle, despite not having a shell, and marks the first branch of the turtle tree of life.
Although it lacked the iconic shell of modern turtles, the creature, dubbed Eunotosaurus africanus, had very wide ribs and a distinctive circular torso that has scientists calling it a prime candidate to help solve the murky history of the origins of turtles.
"Eunotosaurus is a critical link connecting modern turtles to their evolutionary past," says Gaberiel Bever, an assistant professor of anatomy at the New York Institute of Technology. "This is the fossil for which science has been searching for more than 150 years. You can think of it as a turtle, before turtles had a shell."
The creature, around a foot long, was a mixture of features from its own lizard-like ancestors and some early turtle-like qualities that, over many millions of years, would evolve to those seen in turtles today, the researchers report in the journal Nature.
"Think of your neighborhood box turtle, but much more flattened and with scaly skin and a long tail," says Bever in describing the ancient animal. "And teeth, it had a mouthful of them."
Eunotosaurus fossils have been found around South Africa since the 19th century, igniting long-standing debates about whether they were part of turtles' evolutionary lineage.
Bever and his research colleagues utilized advanced scanning techniques to analyze skull anatomy to help confirm Eunotosaurus as the oldest-known representative of the turtle group.
That debate over the evolution of turtles and the way they are related to the other kinds of living reptiles, such as snakes, lizards and crocodiles, has been around since the theory of evolution has first proposed, Bever notes.
"Turtles have been missing their Archaeopteryx, their missing link to the rest of the vertebrate tree, since Darwin told us that we should be looking for one," says Bever, referring to the fossil discovery of the world's oldest-known bird.
In Eunotosaurus, science now has a creature representing a transitional form taking us "from an almost lizard-like creature to the modern turtle body plan that is so interesting and bizarre," he says.
Eunotosaurus lived during the Permian Period 30 million years before the first dinosaurs, and 50 million years before the earliest-known turtle with a fully-formed shell, the researchers say.
