The discovery of Pappochelys, a Triassic-era reptile with a set of emerging turtle-like features, is helping scientists fill in an important evolutionary gap.
Creationists have a tendency to declare any gap in the fossil record as evidence that Darwinian evolution is flawed. The dearth of transitional species, they argue, poses a huge problem for evolutionary biologists as they attempt to explain the shifts from, say, fish to amphibian, amphibian to reptile, reptile to mammal, and the emergence of such dramatic features as feathers, wings, shells, and mammalian milk.
Paleontologists and evolutionary biologists, on the other hand, are driven by the Darwinian paradigm as they painstakingly work to uncover these missing links. The latest development in this regard is the discovery of a 240-million-year-old reptile in Germany that lived during the Triassic Period. Named Pappochelys—meaning “grandfather turtle”—the creature was a blend of lizard- and turtle-like traits. The details of the discovery now appear at the science journal Nature.
“Pappochelys indeed forms a missing link for two reasons,” noted paleontologist and study lead author Rainer Schoch of Germany’s State Museum of Natural History Stuttgart in a Reuters article. “It is far older than all so far known turtles. And its anatomy is more primitive in many features, showing the ancestral condition of various body regions.”
Image: (a) Restoration of the skeleton of Pappochelys in lateral view (as yet unknown elements in white; preserved bones in grey; trunk ribs and gastralia highlighted in black); (b) successive appearance of key features of the turtle body plan; (c) plastron of Odontochelys and reconstructed ventral bones of the shoulder girdle and gastralia set in Pappochelys (elements of the shoulder girdle and their homologues are indicated in a darker shade of grey).
Pappochelys, a stem-turtle, is 20-million-years older than the previous earliest-known turtle, Odontochelys from China. As the researchers write in their study:
The ~220-million-year-old stem-turtle Odontochelys from China has a partly formed shell and many turtle-like features in its postcranial skeleton. Unlike the 214-million-year-old Proganochelys from Germany and Thailand, it retains marginal teeth and lacks a carapace [the hard upper shell of a turtle]. Odontochelys is separated by a large temporal gap from the ~260-million-year-old Eunotosaurus from South Africa, which has been hypothesized as the earliest stem-turtle. Here we report a new reptile, Pappochelys, that is structurally and chronologically intermediate between Eunotosaurus and Odontochelys and dates from the Middle Triassic period (~240 million years ago).
Known from 18 fossil skeletons, Pappochelys had a long tail, a broad trunk, and a lizard-like skull. But it also featured belly armor composed of thick, rib-like bones that were starting to fuse to each other in many places. The paleontologists say it’s an important stage in the evolution of the turtle shell.
“Transitional creatures are the most important contribution that paleontology can make to the study of evolution. They are often unexpected and show surprising features,” added Schoch. “They show how complicated structures like the skull or turtle shell formed step by step, and also give evidence on the sequence of evolutionary steps.”
Read the entire study at Nature: “A Middle Triassic stem-turtle and the evolution of the turtle body plan”.