Birds evolved from dinosaurs, and some dinosaurs were warm-blooded. Mammals existed at the same time as dinosaurs, and most dinosaurs were vegetarian. Many dinosaurs had some form of intelligence as well.
Modern species of birds evolved from a common feathered ancestor, the theropod, starting around the end of the Jurassic and Cretaceous periods. Even though modern reptiles are cold-blooded, which means that their body temperature fluctuates with the surrounding climate, most carnivorous dinosaurs were more likely to be warm-blooded because of their predatory lifestyle, which is why birds are also warm-blooded. Meat-eating predators like the Tyrannosaurus rex and Giganotosaurus are rare compared to the amount of dinosaurs that had a vegetarian diet. Paleontologists speculate that herbivorous dinosaurs like the hadrosaurs, ornithopods and sauropods grazed on vegetation in herds like modern cattle graze in pastures.
The mammals that lived during the same time period as dinosaurs lived in treetops far away from predators during most of the Mesozoic Era. These mammals were small and furry and looked like mice. Other mammals, such as the 50-pound Repenomamus, hunted dinosaurs. Hunters such as T. rex and Troodon had more grey matter than herbivores like the stegosaurus. These predators had more thinking power than their prey and had a keen sense of coordination and heightened senses.