Dinosaurs are ancestors of animals that we see now
Today this group is represented by birds and crocodiles (some scientists also include turtles in this group). In the past it was much more diverse as it also included all extinct dinosaurs, pterosaurs and many ancestors of the crocodiles.
'There are a number of different features that define a dinosaur, but perhaps the clearest things are to do with modifications to their hips and to their legs,' explains Paul.
'In particular, they make a much stronger connection between the hips and their backbone, and they do that by converting some of their vertebrae into a special modified structure called the sacrum that creates these additional connections to their hips.'
Reptiles have up to two vertebrae fused together into a sacrum, but to be a dinosaur an animal needs at least three. Some modern birds have up to 12 sacra.
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