YUNNAN province, in China, is home to the Luoping formation, a trove of spectacularly preserved fossils of creatures that roamed the seas 240m years ago, during the Triassic period. The latest—and arguably most spectacular yet—is Atopodentatus unicus, described this week in Naturwissenschaften by Long Cheng, of the Wuhan Institute of Geology and Mineral Resources, and his team.

People have been digging up and classifying prehistoric reptiles for more than two centuries, so it might be reasonable to suppose that all the main groups would by now have been identified. Atopodentatus unicus suggests this is not true, for it resembles no other known fossil. Its limbs seem to have evolved into paddles, suggesting it was indeed aquatic, but its toe bones look adapted for walking, as they resemble those in hoofed animals. Also, its pelvis is unusually solid and well-structured for a creature which could rely on the water’s buoyancy to counterbalance the force of gravity. Then there is its head, which is tiny, shovel-shaped and armed with more than 175 teeth, outwardly needlelike and inwardly bladelike, arranged in a way reminiscent of a comb.

And a comb is just what Dr Long thinks they were. But not a comb for grooming. He believes Atopodentatus unicus combed the seabed, and probably also beaches and mudflats exposed at low tide, for buried creatures such as worms. It would have taken in mouthfuls of sand or mud and squeezed them back out through its teeth, trapping its prey in the comb as it did so in the way that a baleen whale traps krill.

The creature’s shovel-shaped head supports this idea, for it would have been easy to push through the sediment. Its need to walk along the bottom while doing so explains the toe bones. And emergence from the water for a bit of beachcombing explains the strong pelvis. Where Atopodentatus unicus fits into the tree of life, then, is a mystery—and a reminder of how little-understood the history of life still is.