Going through the widely-reported 2014 Science paper that suggested non-avian dinosaurs were neither ectothermic nor endothermic (popularly simplified as “cold-blooded” and “warm-blooded”), but occupied a category in-between the two, Stony Brook University, New York, palaeontologist Dr. Michael D’Emic, PhD, concluded that these pre-historic creatures were actually mammals after all.
“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.
By closely examining the methodology used in the paper, he found that the scaling of dinosaurs’ yearly growth rates to daily ones (done in order to standardise comparisons) resulted in widely inaccurate estimations.
“Like most animals, dinosaurs slowed or paused their growth annually, as shown by rings in their bones analogous to tree rings,” which is especially evident in larger animals and those who inhabited very stressful or seasonal environments – both of which characterise dinosaurs.
Another point of criticism D’Emic offered in his paper, published May 29 in Science, is that dinosaurs were analysed apart from living birds (which are warm-blooded animals), even though they all descended from Mosozoic 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.”
After correcting for this statistical error, the idea that dinosaurs were warm-blooded, rather than occupying an intermediate “mesotherm” category, gains a great deal of additional support.
“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,” said Holly Woodward, an Assistant Professor in the Centre for Health Sciences at Oklahoma State University.
Regardless of being in disagreement with the paper’s conclusions, D’Emic said the collected data was of excellent quality and proved indispensable for the formation of his own alternative view.
While Professor Felisa Smith, the lead researcher of the 2014 paper, stands by her team’s conclusions, D’Emic hopes his re-analysis will spur more work on when, why, and how pauses or slowdowns in growth are recorded in bones, which may have implications in the development of other species and in the study of bone diseases such as osteoporosis.