Dinosaurs were endothermic (warm-blooded) like mammals, says paleontologist Dr Michael D’Emic of Stony Brook University.

In a 2014 study, a team of scientists led by Dr John Grady of the University of New Mexico suggested that non-avian dinosaur metabolism was neither endothermic nor ectothermic (cold-blooded) but an intermediate physiology termed ‘mesothermic.’

Based on his knowledge of how dinosaurs grew, Dr D’Emic re-analyzed that study, which led him to the strikingly different conclusion that dinosaurs were more like mammals than reptiles in their growth and metabolism.

“The study that I re-analyzed was remarkable for its breadth – the authors compiled an unprecedented dataset on growth and metabolism from studies of hundreds of living animals. Upon re-analysis, it was apparent that dinosaurs weren’t just somewhat like living mammals in their physiology – they fit right within our understanding of what it means to be a ‘warm-blooded’ mammal,” Dr D’Emic said.

He re-analyzed the 2014 study from two aspects. First, the study had scaled yearly growth rates to daily ones in order to standardize comparisons.

“This is problematic, because many animals do not grow continuously throughout the year, generally slowing or pausing growth during colder, drier, or otherwise more stressful seasons,” said Dr D’Emic, author on the paper published in the journal Science.

“Therefore, the previous study underestimated dinosaur growth rates by failing to account for their uneven growth. Like most animals, dinosaurs slowed or paused their growth annually, as shown by rings in their bones analogous to tree rings.”

“The growth rates were especially underestimated for larger animals and animals that live in very stressful or seasonal environments – both of which characterize dinosaurs.”

The second aspect of the re-analysis with the original study takes into account that dinosaurs should be statistically analyzed within the same group as living birds, which are also warm-blooded, because birds are descendants of Mesozoic dinosaurs.

“Separating what we commonly think of as ‘dinosaurs’ from birds in a statistical analysis is generally inappropriate, because birds are dinosaurs – they’re just the dinosaurs that haven’t gone extinct.”

“Re-analyzing the data with birds as dinosaurs lends more support that dinosaurs were warm-blooded, not occupants of a special, intermediate metabolic category.”

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M. D. D’Emic. 2015. Comment on “Evidence for mesothermy in dinosaurs.” Science, vol. 348, no. 6238, p. 982; doi: 10.1126/science.1260061