Ancient reptiles' long necks made them vulnerable to decapitation

Fossils of two Triassic reptiles show severed heads and necks with bite marks, highlighting a drawback of the extremely long necks common to many ancient sea creatures.

“We provide the first tangible proof that this body plan was, at least in some animals, a weak spot,” says Eudald Mujal at the Stuttgart State Museum of Natural History in Germany.

Tanystropheus, a genus of reptiles that lived in the Triassic Period, had stiff necks up to 2 metres long that may have allowed them to capture fish and other animals with their crocodile-like heads while keeping their bodies less visible on the sea floor.

Mujal and his colleague Stephan Spiekman, also at the Stuttgart museum, used high-resolution photography and 3D modelling to assess the fossils of two species, Tanystropheus hydroides and Tanystropheus longobardicus, on display at the University of Zurich, Switzerland.

The 242-million-year-old specimens included two complete, well-preserved skulls and two equally well-preserved, but abruptly shortened spines – with one animal having only 10 of its 13 neck vertebrae, and the other only seven. Both necks had multiple bite marks, including one that showed the telltale signs of a break caused by a violent impact, the researchers say.

Traces of teeth in both specimens reveal that a predator attacked from behind and above, crushing and completely severing the neck. In one specimen, a predator appeared to have bitten into the bone and then pulled back. The bites were so far below the head that the animals probably didn’t see their attackers coming, says Mujal.

Combining clues from the animals’ marine habitats near what is now the Swiss-Italian border and the kinds of tooth marks on their bones, the researchers concluded that the long-necked reptiles were likely to have been decapitated by other species of marine reptile, probably Nothosaurus giganteus, Cymbospondylus buchseri or Helveticosaurus zollingeri.

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While the purpose of Tanystropheus’s elongated neck is still unclear, Spiekman says it may have lifted the reptile’s head high above its body, giving it access to unsuspecting fish and other marine animals. “We think it just sat there and waited for its prey to come to it – which is something modern crocodilians do as well,” he says. It was unlikely to help the animals breathe surface air while staying deep underwater, as pressure differences would make the breathing inefficient, he adds.

The findings suggest that the evolutionary advantage of the long neck came, ironically, with the risk of the animals losing their own heads through predator attacks, the researchers say. Even so, that risk didn’t outweigh the benefits, as the long-necked body plan was “very, very successful” – lasting 175 million years and occurring throughout the ancient world, says Mujal.