The endothermy might have evolved gradually in these small mammal-ancestors, at the beginning by performing muscle-movements or shivering in the early dark hours after sunset to maintain the optimal peeks of their ambient temperature, and they must be active at lower temperature, they have a problem, especially if they are small animals. Bulky animals might "storage" the high body-temperature to save it for For the first many years after their discovery it was generally held that the dinosaurs were reptiles. They were extraordinary large reptiles and in many respects very different from recent reptiles, lizards, crocodiles,