Nearly 250 million years ago, a very odd reptile patrolled the shorelines and coves of the Triassic Alps. Called Tanystropheus, it had a toothy head and a body echoing that of modern monitor lizards. But between them stretched a horizontal, giraffelike neck.

The question of how this 20-foot creature used that 9-foot neck has bedeviled paleontologists for more than 100 years, and it is seen as “one of the most baffling animals that ever lived,” said Stephan Spiekman, a paleontologist at the University of Zurich, in Switzerland. “How could this animal even breathe or swallow? And then there is the evolutionary question: Why on earth did this animal evolve this ridiculously long neck?”

But research published last week in Current Biology, including a new reconstruction of its skull, shows evidence that its body was primed for an aquatic hunting strategy and that the creature came in two varieties: regular and miniature-size.

Tanystropheus was initially described in the 1850s, based on a few tubelike bones. Only in the 1930s, when more complete fossils emerged from the Monte San Giorgio in Switzerland, did scientists realize they were looking at neck vertebrae from a strange reptile whose way of life they couldn’t figure out.

It took decades until paleontologist Karl Tschanz showed in 1988 that ribs underneath the neck vertebrae interlocked, forming a horizontal and extremely stiff neck. That suggested an aquatic lifestyle, Spiekman said, because such an unbending neck would have made life on land inconvenient. But paleontologists continued to argue whether Tanystropheus actively pursued underwater prey or perched onshore, using its long neck like a fishing pole.

To make matters more confounding, digs had found multiple skeletons of smaller Tanystropheus on Monte San Giorgio. If they belonged to juveniles, as some suggested, why did they have different teeth?

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Spiekman’s team sought answers first by CT-scanning a specimen of Tanystropheus’ head from a Zurich museum and reconstructing it, which proved difficult because “all the bones were jumbled together and because the skull of Tanystropheus is very different from other reptiles in many respects.”

“I very clearly remember the day the model was finished and I was the first to see the face of this animal after 242 million years,” he said.

The reconstructed skull revealed several aquatic adaptations: nostrils positioned on the top of the snout, like a crocodile, and long, curved fangs. Instead of pursuing prey actively, Spiekman said, it probably ambushed prey in murky water, lunging forward with its long neck to snap up fish.

To test whether the bones of the smaller Tanystropheus belonged to juveniles or a separate species, the team studied thin sections of bone prepared by Spiekman’s supervisor and co-author, Torsten Scheyer. A close look at the little bones’ interior revealed clear signs of a fully grown adult. That meant that two distinct species of Tanystropheus were coexisting in the same waters: one large, one mini.

The two closely related animals seem to have gone after different types of prey, the team reports, in an example of the phenomenon known as niche partitioning. The larger animal — newly named Tanystropheus hydroides — used its spiked teeth for hunting fish and squid; the smaller species’ teeth point toward a diet of marine invertebrates such as shrimp.

With two mysteries solved, Spiekman and his team hope to take a fresh look at the biomechanics of the jaws and that long, strange neck.

“People always thought that Tanystropheus was an evolutionary dead end,” he said. “But the fact that Tanystropheus evolved into different species with very different lifestyles indicates that Tanystropheus and its neck were quite successful in evolutionary terms.”