Dinosaurs were Mesotherms, neither warm nor cold blooded
Posted by Clinton Hesler on 14th June 2014

Due to lack of solid evidence, it’s debated since long by paleontologists whether dinosaurs were warm-blooded like birds and mammals known as ‘endotherms’ or cold- blooded like reptiles, fish and amphibians known as ‘ectotherms’. But now this age long question has an answer. Scientists from the University of New Mexico (UNM), published a study in this week’s issue of the journal Science which says that the dinosaur blood was neither warm nor cold but had the in-between, ‘Goldilocks’ nature.

Researchers say that Dinosaurs who roamed the Earth for 135 million years who became extinct in a cataclysmic event had a blood that ran neither hot nor cold, but was a kind of in-between that’s rare in the present age. Modern day animals are either warm-blooded endotherms, like humans, dogs and birds who are able to keep a near-constant level of heat, or cold-blooded ectotherms, such as snakes and turtles who constantly move in and out of sunlight, trying to maintain their body temperature.

During the study 21 species of dinosaurs, including the predators Tyrannosaurus and Allosaurus, the long-necked Apatosaurus, the duck-billed Tenontosaurus and the birdlike Troodon as well as a range of mammals, birds, bony fish, sharks, lizards, snakes and crocodiles were assessed. Scientists evaluated the metabolism of numerous dinosaurs using a formula based on their body mass, as revealed by the bulk of their thigh bones and also by using a method that’s akin to studying growth rings in trees estimated they their growth rates as reflected by the rings seen in fossilized bones.

According to lead researcher and graduate student John Grady, most dinosaurs followed an intermediate metabolic path between being warm-blooded or cold-blooded and hence they were mesothermic or goldilocks. A mesotherm body system is believed to have allowed the dinosaurs to move quickly, due to which they didn’t require to constantly eat to maintain body temperature.

“Most dinosaurs were probably mesothermic, a thermally intermediate strategy that only a few species – such as egg laying echidnas or great white sharks – use today”, said John Grady. Evolving a mesothermic metabolism may have helped dinosaurs to grow much larger than was possible for any mammal. Warm-blooded animals have to spend a lot of their time eating to maintain their high metabolic rate. This makes it “doubtful that a lion the size of T. Rex could eat enough to survive,” Grady told Reuters. These findings could help shed light on how warm-blooded animals such as humans evolved.