Turtles are ponderous reptiles with shells and beaks. They also have short tails. Now, though, paleontologists have found a missing link in turtle evolution, which turns out to be a 6-foot-long (nearly 2 meter) monster from the Triassic Period with a tail longer than its body and a formidable beak – but no shell, they report in Nature this week.
Confusingly, earlier and contemporary turtles had no beak but had at least the precursor of shells. The other proto-turtles also had teeth, which Eorhynchochelys sinensis does not.
Scientists admit that the discovery of Eorhynchochelys, which translates into “dawn beak turtle from China” and which lived some 230 million years ago, muddies the waters as much as it sheds blessed light on turtle evolution.
The shallow-sea-faring giant was found in Guangling District, Guizhou, southwestern China, by the study’s lead author, Li Chun, of China’s Institute of Vertebrate Paleontology and Paleoanthropology.
“This creature was over 6 feet long, it had a strange disc-like body and a long tail, and the anterior part of its jaws developed into this strange beak,” says Olivier Rieppel, co-author and a paleontologist at Chicago’s Field Museum. “It probably lived in shallow water and dug in the mud for food.” It had the claws to do so, as today’s turtles do as well. By the way, the biggest turtles today can max out at 8-feet-plus in length.
So what came first, the shell or the beak? Maybe both, if not in the same pre-turtle, according to a newish theory called “mosaic evolution.”
Put one way, Eorhynchochelys shares some characteristics with a pre-turtle that lived 240 million years ago, Pappochelys (“grandfather turtle” in Greek), which paleontologists think was a step on the road to true turtlehood. It also shares other traits with another pre-turtle, Odontochelys.
Pappochelys was found in a quarry in Baden-Württemberg, Germany. It was a tiny thing, only 20 centimeters long. Though maybe it was juvenile. Who knows after 240 million years?
Pappochelys had what paleontologists call “emerging turtle features”: disc-shaped body, small skull, long tail and apparently the precursor of a shell. No beak. It did have teeth. Pappochelys was a sort of a transition between ancestral lizards and future turtles.
Odontochelys lived contemporaneously with Eorhynchochelys in the Triassic Period. Like Pappochelys, it had no beak either and did have teeth. It also had a bottom shell (called a plastron), but no top shell (carapace).
Now we have the slightly later Eorhynchochelys with the earliest known turtle beak, but no teeth or shell. In some things it resembles Pappochelys, in others it resembles Odontochelys.
This mess of traits is the stuff of paleo-nightmares – and more research grants. These turtles are starting to feel like the hominins running all over Eurasia and Africa with mixes and matches of characteristics. Who mixed and matched, resulting in hybrids with new collections of characteristics.
Not every ancestral group has the same combination of traits, explain the scientists. But traits can come together, including by inter-species mating: Just this week scientists announced finding a first-generation Neanderthal-Denisovan hybrid.Mosaic evolution is when traits evolve independently in different ancestral populations, but wind up being demonstrated in a given species.
Some primordial turtles had partial shells, some had beaks and, eventually, these traits occurred in the same animal. The rest is turtle history.
Nick Fraser, an author of the study from National Museums Scotland, noted that early turtle evolution was evidently not a straightforward, step-by-step linear accumulation of unique traits. It was, he thinks, “a much more complex series of events.”
Finally, close examination of Eorhynchochelys’ skull solved another turtle evolution conundrum. Yes, they are related to advanced squamates – snakes and lizards, and not to the more primitive lizards called anapsids. The end.