In the long debate over whether dinosaurs were warm or cold blooded, a study published last year in Science was thought to have put the issue to rest. Dinosaurs were neither, according to the paper. Instead, they occupied an intermediate category. But a reanalysis of the same data has drawn new conclusions. And the verdict this time? Warm blooded.
In a new paper published today in Science, Michael D'Emic, a paleontologist at Stony Brook University, revisited the age-old question of dinosaur 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, evidence for mesothermy in dinosaurs" D'Emic says, in reference to the previous paper.
"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."
D'Emic based his study on something he knows all too well: dinosaur bones. D'Emic specializes in bone microanatomy - the minute structures that make up skeletal tissue. He focused on growth rates among dinosaurs, which he believes were underestimated in the previous study.
The earlier research scaled yearly growth rates down to daily rates, in order to standardize their comparisons. And this is where D'Emic believes the scientists went wrong.
"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" D'Emic says.
"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."
D'Emic also claims the dinosaurs in the previous studies should have been analyzed within the same group as living birds, since birds are directly descended from dinosaurs and are also warm blooded.
"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."
And how do the authors of the previous paper feel about D'Emic's reanalysis?
"We disagree with his central criticisms, and we emphasize that all of our original conclusions stand," University of New Mexico biologist coauthor of the previous study, John Grady says.
"Comparing dinosaur growth with the observed growth rate of living vertebrates clearly shows that non-avian dinosaurs were mesotherms," says Grady.
Other scientists are emphasizing the bigger picture. Holly Woodward, an assistant professor in the Center for Health Sciences at Oklahoma State University, believes that, theories aside, the ability to question and reanalyze primary data is critical to any scientific endeavor.
"D'Emic's study reveals how important access to the data behind published results is for hypothesis testing and advancing our understanding of dinosaur growth dynamics," says Woodward.