Paleontologists Discover Oldest Mammalian Tooth Marks

Posted on June 17, 2010

Ancient Mammalian Tooth Marks

Paleontologists discovered the oldest mammalian tooth marks on the bones of ancient animals, including several large dinosaurs. The findings were reported in a paper published online in the journal Paleontology on June 16. The image above is a close-up of the tooth marks gouged into the rib bone of a large dinosaur by a small mammal that lived 75 million years ago.

Nicholas Longrich of Yale University and Michael J. Ryan of the Cleveland Museum of Natural History came across several of the bones while studying the collections of the University of Alberta Laboratory for Vertebrate Palaeontology and the Royal Tyrrell Museum of Palaeontology. They also found additional bones displaying tooth marks during fieldwork in Alberta, Canada. The bones are all from the Late Cretaceous epoch and date back about 75 million years.

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

The researchers believe the marks were made by mammals because they were created by opposing pairs of teeth. This is a trait seen only in mammals from that time period. They think they were most likely made by multituberculates, an extinct branch of mammals that resemble rodents and had paired upper and lower incisors. The paleontologists 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 animals that made the marks were about the size of a squirrel. Longrich says, "The bones were kind of a nutritional supplement for these animals."

Photo: Nicholas Longrich/Yale University

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