Dinosaur bones made a handy food supplement

In life, dinosaurs struck terror into the mammals they lived alongside. In death, they provided them with a handy source of calcium.

That's the conclusion of palaeontologists who have reinvestigated tooth marks found on dinosaur bones.

It was previously thought that these marks were made solely by other dinosaurs. The distinctive bites of tyrannosaurs, including Tyrannosaurus rex and its smaller relatives, are common on late Cretaceous fossils from Alberta in Canada, says Nick Longrich of Yale University. "If you go through fossil collections at random, you'll see a fair percentage with bite marks from tyrannosaurs."

But two bones dating back 75 million years at the Royal Tyrrell Musuem in Drumheller, Alberta, have different markings, Longrich discovered. These suggested that animals with pairs of closely spaced incisors in their upper and lower jaws had dug into the bones in the same way a person's teeth dig into corn on the cob.

The size and separation of the scratches indicated the animals were mammals similar in size to a modern chipmunk or squirrel.