John Grady, a biologist from the University of New Mexico, and his team have determined that dinosaurs were neither warm blooded, nor cold blooded, but somewhere in the middle.

Dinosaurs: In Between Cold And Warm Blooded

Grady and his team developed a way to determine and analyze a dinosaur’s metabolic rate based on research done on growth rates and energy use of dinosaurs.

“We found that growth rate is a good indicator of energy use in living animals. Warm-blooded (endothermic) mammals grow up 10 times faster than cold-blooded (ectothermic) reptiles, and metabolise 10 times faster; in general doubling one’s metabolic rate leads to a doubling in growth rate,” Grady explained.

When turning their focus to dinosaurs, Grady found that their metabolic rates did not match those of a mammal or those of a reptile, instead, “they occupied the middle energetic ground.”

“They had growth rates and matabolisms intermediate to warm-blooded and cold-blooded organisms of today. In short, they had physiologies that are not common in today’s world,” said University of Arizona biologist Brian Enquist.

Grady hypothesizes that mesothermic animals, such as dinosaurs, kept their edge over reptiles and mamals by maintaining their in between metabolism. The higher metabolism made them faster, but their lower metabolism made them need less fuel to grow.

“A higher metabolic rate gave them other competitive advantages as well: they could grow faster and reproduce faster. But being completely warm-blooded like a mammal limits the maximum size an animal can reach – it is doubtful that a lion the size of a T. rex would be able to eat enough wildebeasts (or elephants) without starving to death. With their lower food demands, however, the real T. rex was able to get really big while still maintaining their advantage over their competition,” Grady said.