The team found that both mammals and plesiosaurs – long-necked marine reptiles – independently evolved elevated metabolisms. Pterosaurs and dinosaurs, which together form a group called Ornithodira, appear to have descended from warm-blooded ancestors — a condition that persisted in long-necked sauropods, predatory theropods such as on theJanosaurus rexAnd their surviving feathered descendants, like chickens.
The presence of highly metabolized sauropods is unexpected, says Stephen Brusatte, a paleontologist at the University of Edinburgh who was not involved in the study. Researchers have suggested in the past that if any dinosaurs had a lower metabolism, they would have been gigantic, lumbering herbivores.
“Just imagine hundreds or thousands of pounds of plants that they would have to eat every day to fuel such a rapid metabolism,” Dr. Brusatte said.
Still, the team’s findings on another group of dinosaurs – the large, diverse family of herbivores called ornithischians – are still more surprising. While the ancestors of ornithischians participated in the metabolism of other warm-blooded dinosaurs, Dr. Weiman said, their greater descendants such as Stegosaurus and Triceratops actually reduced their metabolisms over time, ending up at metabolic rates closer to those of modern reptiles. And like modern reptiles, they may have needed to maintain their core temperature through behavior — basking in the sun or migrating seasonally to warmer climates.
Jingmay O’Connor, associate curator of fossil reptiles at Chicago’s Field Museum, who was also not involved in the study, said. “This work will fundamentally change how we interpret the lifestyles and behaviors of these animals.”