New fossil discoveries from China are yet again turning evolutionary history on its head. This time they've discovered large (~ 1 meter long) mammals living in the Jurassic that were actually preying on dinosaurs. The dating pushes back the time large mammals were thought to exist by a full 65 million years. The two types, Repenomamus giganticus and Repenomamus robustus, were members of a poorly understood group of mammals, the tricodonts, which may have died out even before the dinosaurs. Quite a step up from squeaking mouse-things scrabbling in the bush, eh?