Fossils Show How Long-Necked Reptiles Lost Their Heads

In 1830, Henry De la Beche, an English paleontologist, composed a painting of “Duria Antiquior,” a vision of Mesozoic oceans. When picturing a long-necked marine reptile, he depicted its throat clamped between the jaws of a monstrous Ichthyosaurus.

Almost two centuries have passed without direct evidence of the neck biting De la Beche imagined. But research published Monday in the journal Current Biology has provided gory — and extremely rare — evidence that predators saw the lengthy, outstretched necks of reptiles swimming around prehistoric seas as an irresistible target.

The victim was Tanystropheus, whose neck is “completely unique” in the fossil record, said Stephan Spiekman, a paleontologist with the State Museum of Natural History in Stuttgart, Germany, and an author on the study. The structure — which made up half the animal’s body — was constructed from 13 bizarrely elongated and interlocking vertebrae, creating a neck as stiff as a fishing rod.

“Getting any insight into how these extreme structures functioned with potential weakness and strengths is very important,” Dr. Spiekman said.

Dr. Spiekman’s doctoral research revealed that two separate species of Tanystropheus — one small, another almost 20 feet long — lived in the shallow lagoons of the Triassic Alps, most likely hunting fish from perches on the seafloor. In the course of that research, Dr. Spiekman studied a pair of specimens from both species, each composed solely of a head and neck.

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

Dr. Spiekman shared the specimens with his office mate, 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 apart.

“The broken portion of the bones look like if you break a chicken bone,” Dr. Mujal said. “The bone was broken when it was still fresh, and most likely while the animal was still alive.”

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

Both animals had most likely been struck from above, the team concluded, possibly by a predator interested more in their meaty bodies than their spindly necks or tiny heads. “They’re possibly preferentially targeting the same region of the neck,” Dr. Mujal said, “far enough away from the head to make it hard for the animal to defend itself.”

Tanystropheus is the only marine reptile known to suffer such unceremonious decapitation. The long necks of plesiosaurs — reptiles that emerged after Tanystropheus went extinct and lingered until the end of the Mesozoic period — are made up of many bulky vertebrae, all buried in muscle and blubber, Dr. Mujal said. While they may also have gotten it in the neck, “a very thick layer of flesh and skin around the neck means that predators might not have left any marks on the vertebrae.”

But even if the long neck was a weak spot for predators, the researchers note, it was clearly a remarkably successful evolutionary strategy. Many different groups of fish-eating marine reptiles independently evolved elongated necks over 175 million years. Even Tanystropheus’s family proved a success story, spreading across Triassic shorelines from modern Europe to China and lasting for 10 million years.

“Evolution is a game of trade-offs,” Dr. 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 can be worth it for the species — even if you personally get your head bitten off.

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