Thermoregulation
Thirdly, almost all endotherms are insulated to reduce heat loss. Obviously that is true of birds (which have feathers) and land mammals (which have fur). Marine mammals have thick layers of fat under their skin, which is better insulation than wet fur. The exceptions are some very large mammals such as elephants, which have almost no fur. Their problem is how to get rid of heat, and that is a problem for all really large land animals. The African elephant's solution is to have large ears, which are well supplied with blood vessels, and to wallow in water if that is available. It is very likely that the same problem affected large dinosaurs. After all, the largest titanosaurs were far larger than any land animal alive today.