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Dinosaurs Were Warm-Blooded?

May 28, 2015 11:30 PM EDT

Dinosaurs are often viewed as cold-blooded prehistoric predators, however, new research shows that they were likely warm-blooded.

This is a very different conclusion than a widely publicized study published in 2014, which concluded that dinosaurs couldn't make up their minds. Meaning, they were neither ectothermic nor endothermic - terms popularly simplified as "cold-blooded" and "warm-blooded," respectively - but rather they occupied an intermediate category.

But now, according to paleontologist Michael D'Emic from Stony Brook University, who re-analyzed this popular study, dinosaur blood was indeed one-sided.

"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," D'Emic said in a statement. "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," he added.

D'Emic specializes in bone microanatomy, or the study of the structure of bone on scales that are just a fraction of the width of a human hair. Based on this background, he reached a strikingly different conclusion that dinosaurs were more like mammals than reptiles in their growth and metabolism.

During his re-analysis, D'Emic approached the study from two aspects. First, the original study had scaled yearly growth rates to daily ones in order to standardize comparisons, which he deemed problematic because "many animals do not grow continuously throughout the year, generally slowing or pausing growth during colder, drier, or otherwise more stressful seasons."

"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," he explained.

The growth rates were especially underestimated, according to his study, 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 took into account the fact 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," D'Emic said.

By re-analyzing the data with birds as dinosaurs, his findings indicate that dinosaurs were most likely warm-blooded creatures, and did not belong to a special, in-between category.

The results were published in the journal Science.

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