Were Dinosaurs Warm or Cold Blooded?


While dinosaurs have long captured the imagination of people everywhere – so much about their origins remains a mystery. Long has it been argued whether they were warm-blooded or cold-blooded. While plenty of evidence has appeared to support the former, perhaps the question is the wrong one to ask.  We now know that these types are not neat divisions – with some animals such as modern crocodiles being able to routinely switch between being warm and cold-blooded, while enjoying the advantages of both.

Last year, the University of New Mexico biologist John Grady and his colleagues published their new in-depth analysis of dinosaur physiology by studying the growth rates from fossil records. The study concluded that dinosaurs may have been a type of animal known as a mesotherm – which means that they were capable of regulating their bodies at a higher temperature than their habitat, but that there was no set point to it, meaning that there was no calorie limit set for them to maintain a set temperature.

Not everyone bought it. In the new issue of Science, both Stony Brook University paleontologist Mike D’Emic and Nathan Myhrvold refuted the idea in two separate stories.

Myhrvold’s maintains that when working, Grady and colleagues “deviated from accepted statistical practice” as they estimated the growth rate, therefore formulating an “illusion” of mesothermic dinosaurs. Myhrvold concludes “growth rate does not predict metabolism.”

D’Emic found another critical flaw in the study – while dinosaur lifespans were determined by rating yearly growth spans of bone, it is likely that they grew at different rates during different seasons, while the study also fails to account for time differences in days and years in the Mesozoic Era.

What D’Emic found when he doubled the rates, to account for longer periods of growth, was rates indicative of endothermic metabolisms – similar to placental mammals. However, this does not necessarily indicate that all of them were hot-blooded, just that this would be a more accurate calculation based on Grady’s accumulation of data. The findings of the Dinosaur Renaissance still remain as invaluable to paleontology as ever – whether dinosaurs were agile and intelligent is no longer in dispute, but the debate over what physiology allowed them to thrive continues to be a strongly debated mystery.

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About the author

Kristin covers health, science and internet news.