In the past, paleontologists assumed that all dinosaurs were cold-blooded like today's reptiles. But beginning in the 1960s, some scientists began raising the possibility that some dinosaurs were warm-blooded.

In warm-blooded mammals, cross-sections of their bones show many channels for the internal passage of blood. In contrast, cold-blooded reptile bones have far fewer blood channels. Significantly, bones from some types of dinosaurs show a combination of both patterns, with lots of blood channels in the bones of juveniles, and fewer in adults. Dinosaur bones found on the North Slope and studied thus far exhibit the juvenile pattern, but the debate about this matter is far from settled. It may be that dinosaurs had a unique type of metabolism unlike any living animals today.