The long-necked marine reptiles known as plesiosaurs are one of the icons of the dinosaur age. But all the fossil skeletons found so far come from the Jurassic period. Now we’ve found a nearly complete fossil from the earlier Triassic period. It is the oldest plesiosaur ever found.
The fossil shows that, as predicted, plesiosaurs evolved in the late Triassic and survived the mass extinction that ushered in the Jurassic era 200 million years ago. All other marine reptiles, apart from the dolphin-like ichthyosaurs, died out.
The 2-metre-long fossil is thought to be a juvenile. It was found in 2013 in a clay pit in Germany and acquired by a private collector, who notified authorities. Now Martin Sander of the University in Bonn and colleagues have published a full description of the find.
There is no doubt that the fossil is a plesiosaur, says Sander. It has all the group’s key traits.
Crucially, the team confirmed that it dates to the Triassic period. “We went to the pit and convinced ourselves that we are looking at the Triassic,” Sander says.
The great diversity of plesiosaurs found in the early Jurassic suggests at least six lineages survived the end-Triassic extinction. But until now only a few bone fragments, tentatively identified as plesiosaur remains, have been found.
“Very early in the Jurassic there are lots and lots of plesiosaurs, as if they appeared from nowhere. So everyone was expecting to find a plesiosaur from the Triassic,” says Roger Benson of the University of Oxford. “But until you actually find it you can’t know what it’s going to look like.”
At the beginning of the Triassic, a wide range of reptiles colonised the seas. Some evolved long, flexible necks with up to 70 vertebrae – more than any other vertebrates. These “snake-necked” marine reptiles gave rise to plesiosaurs late in the Triassic, the new find confirms.
But contrary to many early depictions, plesiosaurs had stiff necks that could not bend much, which is puzzling. “If you have a long neck and you stiffen it, what is it good for?” asks Sander. He thinks they were ambush predators: their long necks and small heads may have let them sneak up to unsuspecting fish in murky waters.