Were Dinosaurs Warm-Blooded or Cold-Blooded?

Wednesday, December 7, 2016

Growth rates across an evolutionary tree. Dinosaurs growth rates fall in between warm blooded mammals and birds ('endotherms') in red, and cold-blooded fish and reptiles ('ectotherms') in blue. They are closest to living mesotherms. Credit: John Grady.


Because dinosaurs are classified as reptiles, one might assume that they are cold blooded, but some scientists suggest that dinosaurs may have been somewhere between cold and warm blooded. Though most animals fall into either category, there have been some intermediary species known to science, with dinosaurs potentially being one of this number.

Dinosaurs as mesotherms by John Grady


The lack of certainty and the assertion that dinosaurs may have been neither warm nor cold blooded stems from the fact that birds, which may be the dinosaurs’ closest living relatives, are warm blooded, unlike modern reptiles, which are cold blooded. There is also evidence to suggest that dinosaurs had faster metabolisms than cold-blooded animals typically have.

Dinosaurs were neither warm nor cold blooded

Depending on the source of an organism’s body warmth, it may be classified as either an ectotherm or an endotherm. An ectotherm is an animal that warms itself primarily by obtaining heat from the environment, perhaps by sunning itself. Ectothermic animals include most fish, amphibians, and reptiles as well as most invertebrates. An endotherm is an animal that produces most of its own heat and maintains a constant body temperature even when environmental temperatures fluctuate. All birds and mammals are endotherms.

Paleontologists have struggled for years to determine whether dinosaurs were cold-blooded like today’s reptiles or warm-blooded like most modern mammals and birds.

It turns out the answer is neither. Scientists have found evidence for “mesothermy” in dinosaurs. The “mesothermy” found in dinosaurs likely allowed them to move quickly, given that they would not need to constantly eat in order to maintain their body temperature (as do endotherms). As well, the dinosaur’s mesothermic metabolic rate would have decreased the vulnerability of these species to extreme fluctuations in external temperature, allowing them to exert some control of body temperature via internal mechanisms.

Source: SciNews.com