Ancient Mammal Tooth Marks in Prehistoric Animal Bones

Scientists have identified the tiny and faint scratch marks made by the teeth of ancient, primitive mammals as they gnawed on the remains of dinosaurs and other prehistoric animals.  In a paper published in the scientific journal “Paleontology”, the researchers from Yale University and the Cleveland Museum of Natural History report on the mammalian tooth marks left on the bones of several fossil bones, including the bones of dinosaurs.

Whilst studying the fossil collections at the University of Alberta Laboratory for Vertebrate Palaeontology at the Royal Tyrrell Museum (Drumheller, Alberta, Canada), Nicholas Longrich of Yale University and Michael J. Ryan of the Cleveland Museum discovered several of the bones showed signs of tooth marks.  Additional bones that seemed to have been gnawed upon were found during fieldwork in Alberta.  All the bones studied date from 75 million years ago (Campanian faunal stage of the Late Cretaceous).

The team discovered tooth marks on a femur bone (thigh bone) from a Champsosaurus, a crocodile-like, aquatic reptile that grew up to 1.5 metres long, the rib of a dinosaur, most likely a herbivorous Hadrosaurid or Ceratopsid; the femur of another large dinosaur that was likely another Ornithischian and a lower jaw bone from a small marsupial.

The researchers believe the marks were made by mammals because they were created by opposing pairs of teeth—a trait seen only in mammals from that time.  They think they were most likely made by Multituberculates, an extinct order of archaic mammals that resemble rodents and had paired upper and lower incisors.  Several of the bones display multiple, overlapping bites made along the curve of the bone, revealing a pattern similar to the way people eat corn on the cob.

Ancient Mammalian Tooth Marks in Fossilised Bone

Picture Credit: Nicholas Longrich (Yale University)

The picture above shows parallel groves cut into the rib bone of a dinosaur, evidence of a mammal gnawing on bones preserved for 75 million years.

The Multituberculates are a mammalian subclass that first appeared in the Middle Jurassic and went extinct in the Eocene.  These mammals were relatively abundant in the northern hemisphere during the Late Cretaceous, probably herbivorous; many scientists believe that these creatures were mainly nocturnal.  Many Multituberculates resembled rodents although they were not closely related to modern placental mammals.

A Diagram Showing a Typical Multituberculate Skull

Tooth Marks

Picture Credit: Nicholas Longrich (Yale University)

The diagram shows the typical skull of a Multituberculate mammal, showing that the tell-tale tooth marks found in the bone were probably made by the incisors as the grawed on the bone, not to strip meat but perhaps to gain important minerals and vitamins.  It was these unobtrusive animals that were to outlast the dinosaurs, as the Multituberculates survived into the Cenozoic.

Commenting on the tooth marks, the team conclude that the animals that left evidence of gnawed bones in the mega faunal fossil record of Alberta were probably no bigger than a squirrel.

Nicholas Longrich stated:

“The bones were kind of a nutritional supplement for these animals.”

He went onto add that there were probably a lot more fossils in museum collections and awating discovery that would show this behavioural evidence of primitive mammals.

“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.”

But he points out that the Late Cretaceous creatures that chewed on these bones were not nearly as adept at gnawing as today’s rodents, which developed that ability long after dinosaurs went extinct.

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