Dimetrodon’s diet redetermined

DALLAS — Dimetrodon chowed down on sharks and amphibians like a prehistoric Pac-Man.

Rather than dining on plant eaters, the reptilian carnivore ate mainly aquatic animals, chomping big bites out of amphibians’ heads as they peeped up out of their burrows, paleontologist Robert Bakker reported October 14 at the Society for Vertebrate Paleontology annual meeting.

“It’s cool and exciting because it’s completely different from what people thought,” said Stephen Hobe, a paleontologist at Carthage College in Kenosha, Wis.

Dimetrodon, one of the first big land predators on Earth, was roughly the size of a small crocodile, with a snub nose, sharp teeth and a towering fin on its back. The creature lived about 280 million years ago — some 50 million years before dinosaurs appeared. For years, scientists thought Dimetrodon fed mainly on herbivorous land critters. “But that turns out to be wrong,” said Bakker, of the Houston Museum of Natural Science.

He and colleagues have spent 11 years cataloging all the bones and teeth in a Dimetrodon-laden fossil pit near Seymour, Texas. The pit is nearly the size of two football fields and includes ancient ponds and floodplains. Bakker’s team has dug up 39 Dimetrodons, but only one each of Edaphosaurus and Diadectes — large herbivores thought to be prime Dimetrodon cuisine.

That’s not nearly enough food to sustain such a large population of predators, said Christopher Flis, a paleontologist at the Whiteside Museum of Natural History in Seymour, who works with Bakker on the project. Other kinds of animals must have made up the difference, Flis said. He and Bakker think those animals were aquatic.

The team unearthed the remains of 134 small sharks (they weren’t as long as Dimetrodon, but carried a wicked-looking head spike) and the dismembered skulls of 88 Diplocaulus, an amphibian with a bulky, boomerang-shaped head. Buried amid the chewed-up bones, researchers found loads of Dimetrodon teeth.

The predator used its teeth to pull amphibians out of the ground — like a gardener yanking up carrots. Diplocaulus’ heavy heads probably popped right off, Flis said. And since “the heads didn’t have that much meat to chew on,” he said, Dimetrodon probably ate the amphibians’ bodies and left the mangled remains behind.