75 mn yr oldest tooth-marks reveal mammals feasted on dino-bones

Washington, June 17 (ANI): Palaeontologists have discovered tooth marks gouged in the rib bone of a large dinosaur by a mammal that lived 75 million years ago.

Researchers Nicholas Longrich of Yale University and Michael J. Ryan of the Cleveland Museum of Natural History think the tooth marks were made by an archaic order of extinct mammals resembling rodents, with each groove corresponding to a single incisor.

The pair discovered tooth marks on a femur bone from a Champsosaurus, an aquatic reptile that grew up to five feet long; the rib of a dinosaur, most likely a hadrosaurid or ceratopsid; the femur of another large dinosaur that was likely an ornithischian; and a lower jaw bone from a small marsupial.

The researchers concluded the marks being from a mammal since they were created by opposing pairs of teeth-a trait seen only in mammals from that time. The mammals are most likely multituberculates, an extinct order of archaic mammals that resemble rodents and had paired upper and lower incisors - which they used to gnaw at the bones for minerals rather than for meat.

"The bones were kind of a nutritional supplement for these animals," said Longrich.

"The marks stood out for me because I remember seeing the gnaw marks on the antlers of a deer my father brought home when I was young," he said.

"So when I saw it in the fossils, it was something I paid attention to."

The findings were published online on June 16 in the journal Paleontology. (ANI)