Paleontologist Michael D’Emic of Stony Brook University has re-examined a 2014 study which claimed that dinosaurs were neither warm, nor cold blooded but instead occupied a middle ground. D’Emic’s research, published in the journal Science, is just the latest chapter in an argument which may never be fully resolved.
When scientists study dinosaurs, all they really have to work with is bone. Because soft tissue doesn’t fossilize well, there is none to analyze and all trace of DNA degraded millions of years ago. Despite what the film Jurassic Park tells you, DNA will not last more than about six million years even if it is inside a mosquito, trapped in amber. So it is difficult to say much for sure about dinosaur physiology.
Dinosaur means “terrible lizard”. For a long time people thought that they were lizards and that, like lizards, they were cold blooded. Through the first half of the 20th century, this was the generally accepted wisdom. Over the last several decades however the majority of research has suggested that dinosaurs were not the slow, sluggish creatures envisioned earlier but were in fact fast moving, warm blooded creatures like mammals.
Last year, a group of researchers led by University of New Mexico biologist John Grady concluded that dinosaurs were likely mesotherms. Mesotherms are rare in the modern world however, common examples include lamnid sharks, leatherback turtles and tuna.
A mezotherm maintains a body temperature higher than its surrounding environment but not at a fixed point. Humans, for example, maintain an average body temperature of 98.6 degrees Fahrenheit. A mezotherm combines internally produced heat with environmentally produced heat and reaches an equilibrium which fluctuates.
D’Emic re-analyzed the data produced by Grady’s team and came to a very different conclusion.
“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,” said Dr. D’Emic.
D’Emic specializes in the study of bone structures on the microscopic level or “bone microanatomy”. He re-analyzed the study based on the prior researchers assumptions about the growth rate of dinosaur bones. The researchers on the previous study scaled annual growth patters into daily patters for standardization.
“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. Therefore, the previous study underestimated dinosaur growth rates by failing to account for their uneven growth,” said D’Emic.
Additionally, he states that dinosaurs should be analyzed within the same grouping as modern, warm-blooded birds.
“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,” he concludes.
While the new study certainly adds to the body of evidence suggesting that dinosaurs were warm blooded, it is a question that will remain difficult to answer with certainty until someone invents a time machine.
