Now we have found what appears to be real dinosaur blood inside a bog-standard fossil bone.

"We stumbled on these things completely by chance," says Susannah Maidment of Imperial College London, whose team was trying to study bone fossilisation by cutting out tiny fragments of fossils.

Instead, they found blood-like cells and collagen from 75-million-year-old dinosaur fossils – 10 million years before T. rex appeared.

 Although the cells are unlikely to contain DNA, those extracted from better preserved fossils using the same technique may do so, she says.

And even without DNA, soft tissue cells and molecules could help us learn much more about dinosaur physiology and behaviour, the team says. For example, the physical size of blood cells can reveal insights into metabolism, and the possible transition from a cold to warm-blooded existence.