May 11, 2016

By Sid Perkins

Some strange creatures cropped up in the wake of one of Earth’s biggest mass extinctions. That includes a plant-eating marine reptile that had a hammerhead skull—a shape previously unknown in the reptilian fossil record. The unusual animal, dubbed Atopodentatus unicus (a blend of Greek and Latin for “unique and strange-toothed”), was first described 2 years ago based on fragmentary fossils. At the time, paleontologists thought the 2- to 3-meter-long reptile had a downturned, flamingolike snout that it used to stir up seafloor sediments as it foraged for mud-dwelling prey. But new, better-preserved fossils suggest that the creature, which lived in what is now south-central China between 243 million and 244 million years ago, actually had different dietary preferences. The front of its broad, T-shaped snout was filled with stubby, chisellike teeth, and the sides of its jaws were lined with closely spaced, needle-shaped teeth, the researchers report today in Science Advances. That arrangement wouldn’t have been too useful for chewing prey. It’s more likely, the team says, that Atopodentatus used its front teeth to nip algae or other plants from rocky surfaces and then, with its mouth closed, forced mouthfuls of water through its side teeth, which acted as a filter. Atopodentatus is thus the oldest known vegetarian among marine reptiles. Overall, the creature is so unusual that it’s difficult to tell where it fits on the reptile family tree, the researchers say. Because its fossils are relatively complete, paleontologists will probably need to unearth fossils of yet-to-be-discovered relatives to better figure this out. In the meantime, Atopodentatus seems to be most closely related to the plesiosaurs, the typically long-necked marine reptiles that often were top predators in dinosaur-era oceans.

http://www.sciencemag.org/news/2016/05/ancient-hammerhead-creature-may-have-been-world-s-first-vegetarian-sea-reptile