Robert T. Bakker - Theories

Theories

In his 1986 work The Dinosaur Heresies, Bakker puts forth the theory that dinosaurs were warm-blooded, his evidence for which includes:

• Almost all animals that walk upright today are warm-blooded, and dinosaurs walked upright.
• The hearts of warm-blooded animals can pump much more effectively than the hearts of cold-blooded animals. Therefore, the giant Brachiosaurus must have had the type of hearts associated with warm-blooded animals, in order to pump blood all the way up to its head.
• Dinosaurs such as Deinonychus led a very active life, which is much more compatible with a warm-blooded animal.
• Some dinosaurs lived in northern latitudes where it would be impossible for cold-blooded dinosaurs to keep warm.
• The rapid rate of speciation and evolution found in dinosaurs is typical of warm blooded animals and atypical of cold blooded animals.
• The predator/prey ratio of predatory dinosaurs to their prey is a signature trait of warm-blooded predators rather than cold-blooded ones.
• Birds are warm-blooded. Birds evolved from dinosaurs, therefore a change to a warm-blooded metabolism must have taken place at some point; there is far more change between dinosaurs and their ancestors, the archosaurs, than between dinosaurs and birds.
• Warm-blooded metabolisms are evolutionary advantages for top predators and large herbivores; if the dinosaurs had not been warm-blooded there should be fossil evidence showing mammals evolving to fill these ecological niches. No such evidence exists; in fact mammals by the end of the Cretaceous had become smaller and smaller from their mammal-like-reptile ancestors.
• Dinosaurs grew rapidly, evidence for which can be found by observing cross-sections of their bones. Warm-blooded animals grow at a similar rate.