For nearly two centuries, fossil hunters have mused that the improbably long necks of some ancient marine reptiles made them tempting targets for hungry predators.
Now, researchers have uncovered grisly evidence that sticking one’s neck out really was a deadly weakness: the remains of two creatures whose heads were snapped off in acts of Triassic violence.
“We think they were grabbed by the neck and killed that way, and because the neck doesn’t have much muscle, the predator left them and focused on the much more meaty body,” said Dr Stephan Spiekman, a palaeontologist at the State Museum of Natural History in Stuttgart, Germany.
Spiekman and his colleague Dr Eudald Mujal, an expert in prehistoric bite marks, made the gruesome discovery while examining a pair of 240m-year-old fossils of tanystropheus, a marine reptile recovered from Monte San Giorgio on the Swiss-Italian border.
At the time, before the emergence of the dinosaurs, the mountain was home to a tropical lagoon. Fossils from the rocks preserve such a spectacular diversity of prehistoric fish, reptiles, crustaceans and other species that it was designated a Unesco world heritage site.
The fossils studied belong to two different species of tanystropheus, one smaller animal about 1.5m long, and another much larger creature about 6m long. In both cases, only the small head and part of the long, slender neck remain. The bodies, ominously, are missing.
Close inspection of the larger fossil revealed two tooth-shaped holes in the vertebrae at the precise point where the neck was cleanly broken. “The whole neck is broken in exactly one plane,” said Spiekman. “The neck was broken in one go, and having the tooth marks there is pretty conclusive evidence that some animal bit its neck off.”
The smaller reptile seems to have suffered the same fate. Again, the neck and slender supporting neck ribs which run parallel along the vertebrae to provide stiffness, were broken at a single point. This time, a small tooth-shaped hole was found further up the neck, away from the fracture point. Scavenging looks highly unlikely, the scientists say,because bite marks look different in dead animals, and scavengers tend to cause far more damage when they tuck in to a carcass.
The evidence suggests that while many marine reptiles reaped clear benefits from exceptionally long necks – the larger tanystropheus had a neck comfortably over 2m – the advantages came with a cost. As depicted in Henry De la Bèche’s 1830 watercolour, Duria Antiquior, a long neck was a great way to lose one’s head.
Based on the size of the teeth marks, Spiekman and Mujal suspect the beheadings were performed by other marine reptiles, perhaps a distant ancestor of the plesiosaur called a nothosaur, an early ichthyosaur, or the stocky helveticosaurus. Details are published in Current Biology.
“These are some of the most macabre fossils I’ve ever seen,” said Steve Brusatte, a professor of vertebrate palaeontology at Edinburgh University, who was not involved in the study. “You can sense the violence of the reptile-eat-reptile world of the Mesozoic when you look at these fossils.”
“It seems like these long necks were a type of superpower, which allowed these reptiles to ambush their prey by darting their heads like a spearfisherman,” he added. “But all superheroes have a weakness, and these long necks would have been kryptonite to these animals, as they left them vulnerable to attack from other reptiles.
“Still, long necks persisted in so many reptile groups, for so long, right up to the asteroid that knocked many of them out, alongside their dinosaur cousins. The value of a long neck must have generally outweighed the costs.”