Fossils show how long-necked reptiles lost their heads

In 1830, Henry de la Beche, an English paleontologist, composed a painting called “Duria Antiquior”, a view of the Mesozoic oceans. By imagining a long-necked marine reptile, he pictured its throat trapped between the jaws of a monstrous ichthyosaur.

Nearly two centuries passed without direct evidence of the neck bite that De la Beche envisioned. But research published Monday in the journal Current Biology provided bloody — and extremely rare — evidence that predators viewed the long, outstretched necks of reptiles swimming in prehistoric seas as irresistible targets.

The victim was Tanystropheus, whose neck is “completely unique” in the fossil record, said Stephan Spiekman, a paleontologist at the State Museum of Natural History in Stuttgart, Germany, and one of the study’s authors. The structure — which made up half of the animal’s body — was formed from 13 bizarrely elongated vertebrae intertwined together, creating a neck as rigid as a fishing rod.

“It’s very important to get an idea of ​​how these extreme structures worked, with possible weaknesses and strengths,” said Spiekman.

Spiekman’s doctoral research revealed that two different species of Tanystropheus — one small and the other nearly 20 feet long — lived in the shallow lagoons of the Triassic Alps, likely hunting fish perched on ledges on the sea floor. In the course of this research, Spiekman studied a pair of the two species, each consisting only of a head and neck.

In both animals, “the neck is broken in half at the back,” Spiekman said. “It’s like breaking a broomstick.”

Spiekman shared the specimens with his colleague Eudald Mujal, a paleontologist who specializes in analyzing predator-prey interactions in fossils, particularly bite marks on bones. After an afternoon with the fossils at their resting place in Zurich, they concluded that the necks had been bitten.

“The broken part of the bones looks like when you break a chicken bone,” Mujal said. “The bone was broken when it was still fresh and probably while the animal was still alive.”

The team measured the distance between bite marks on the larger Tanystropheus and compared them to the jaws of several predators that share the habitat. The likely culprit was either a large notosaur—ancestors of seal-like plesiosaurs—or one of two large predatory ichthyosaurs, Mujal said. The smaller Tanystropheus may have been attacked by a smaller marine reptile or a large fish.

Both animals were likely hit from above, the team concluded, possibly by a predator interested more in their fleshy bodies than their slender necks or tiny heads. “They are possibly preferentially targeting the same region of the neck,” said Mujal, “far enough from the head to make it difficult for the animal to defend itself.”

Tanystropheus is the only marine reptile known to undergo such an unceremonious decapitation. The long necks of plesiosaurs — reptiles that emerged after the extinction of Tanystropheus and remained until the end of the Mesozoic period — are composed of many bulky vertebrae, covered in muscle and fat, Mujal said. While they could also have this on their necks, “a very thick layer of meat and skin around it means that predators might not have left marks on the vertebrae.”

But even if the long neck was a weak point for attracting predators, the researchers note, it was clearly a very successful evolutionary strategy. Several different groups of fish-eating marine reptiles independently evolved elongated necks over 175 million years. Even the Tanystropheus family proved to be a success story, spreading along the Triassic coasts from modern Europe to China and lasting 10 million years.

“Evolution is a trade-off game,” Spiekman said. “In the long run, the risk of having a long neck was worth it for this animal.”

In other words, sticking your neck out might be worth it for the species—even if you personally get your head ripped off.

^{Translated by Luiz Roberto M. Gonçalves}