What evidence suggests that dinosaurs were endothermic?

Answer 1

As far as the largest ones are concerned, their size implies need for great amounds of energy, which means they had to eat a lot. Ectothermic animals don't need enough food, because they produce their energy utilizing the heat of the sun. This way, however, the bigger an animal gets, the more time it takes to generate heat and this may cost its own life, because in the meanwhile other smaller predatory animals have become active and threatening. The largest dinosars had to be endothermic, in order to, at least, stay alive. Some smaller dinosaurs, like Leaellynasaura, have been discovered to have lived in low latitudes near the Antarctic circle, which means they had to be endothermic to stand the climatic conditions. Even more, some small theropods present skeletal characteristics, like V-shaped bone of the chest (Velociraptor), which connects them with birds. Their 3-digit forelimbs, 4-digit long and erect hindlimbs (built for speed) , the structure of metacarpal and their respiratory system are also signs which imply connection with birds and some theropods from China (Sinosauropteryx, Sinornithosaurus etc) even present signs of feathers or proto-feathers. Since feathers imply ability of thermoregulation and, thus, high metabolic rate, scientists believe that some dinosaurs, if not all, eventually became endothermic, even if they had evolved from ectothermic ancestors. The evolutionary connection between dinosaur and endothermic birds is also implied by the discovery that early birds had a snout filled with teeth, long bony tale and digits on front limbs (wings), as well as scaly theropod legs.