Fossils show how long-necked reptiles lost their heads

In 1830 Henry De la Beche, an English paleontologist, made a painting of “Duria Antiquior” a vision of the Mesozoic oceans. In depicting a long-necked marine reptile, he depicted his throat clamped between the jaws of a monstrous ichthyosaur.

Nearly two centuries have passed without direct evidence of the neck-biting that De la Beche imagined. But research published Monday in the journal Current Biology has provided gory—and extremely rare—evidence that predators saw the long, 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 at the State Museum of Natural History in Stuttgart, Germany, and an author on the study. The structure – which made up half of the animal’s body – was made up of 13 bizarrely elongated and interlocking vertebrae, creating a neck as stiff as a fishing rod.

“It’s very important to get some insight into how these extreme structures functioned with potential weaknesses and strengths,” said Dr. Spiekman.

The doctoral research of Dr. Spiekman revealed that two separate species of Tanystropheus — one small, another nearly 20 feet long — lived in the shallow lagoons of the Triassic Alps, most likely hunting fish from seafloor perches. In the course of that research, Dr. Spiekman collected a few specimens of both species, each consisting only of a head and a neck.

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

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

“The broken part of the bones looks like you’re breaking a chicken bone,” said Dr. Mujal. “The bone was broken when it was fresh, and most likely when the animal was 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 nothosaur — seal-like ancestors of plesiosaurs — or one of two large, predatory ichthyosaurs, said Dr. Mujal. The smaller Tanystropheus may have been attacked by a smaller marine reptile or a large fish.

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

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

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

“Evolution is a game of compromise,” said Dr. Spiekman. “In the long run, the risk of 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.