Stony Brook professor challenges dinosaur study, growth rates

Perhaps the makers of the Jurassic Park movies should have consulted Stony Brook University paleontologist Michael D'Emic.

A scientific clash over the temperature of dinosaur blood might reveal how long it would take a dinosaur to grow big enough and mean enough to hunt large prey.

For decades, scientists have debated whether dinosaurs were warm-blooded like mammals or cold-blooded like reptiles.

D'Emic analyzed a 2014 study published in Science magazine, a peer-reviewed journal, which found dinosaurs occupied a midpoint between mammals and reptiles.

Instead, D'Emic concluded that they were warm-blooded. Science published his comments as part of its review process.

"I reanalyzed the data and found that dinosaurs seemed to be indistinguishable from mammals in how they grew and what their metabolism was," he said.

The original researchers from the universities of Arizona and New Mexico have stood by their finding that dinosaurs were "mesotherms," which have more control over their temperature than reptiles, but not as much as mammals.

To calculate a dinosaur's body temperature, those researchers examined how fast it grew, which shed light on its metabolic rate. The slower a dinosaur's metabolism, the cooler its temperature, and thus the more reptilelike.

Like trees, cross-sections of dinosaur bones reveal growth rings, a feature also shared by many mammals.

"Did they grow quickly, like a mammal, or even faster, like a bird, or even slower, like a crocodile?" asked D'Emic, noting that a 2-year-old ostrich can top 100 pounds.

The study he re-examined analyzed hundreds of mammals and reptiles and nearly two dozen dinosaurs. But D'Emic said the research did not factor in the way growth rates vary in a year, pausing when food might be scarce, as in winter.

"The previous study underestimated dinosaur growth rates by failing to account for their uneven growth," he said.

When he essentially doubled the dinosaur growth rates, he found they resembled mammals.

D'Emic reached the same conclusion when he compared dinosaurs with birds, instead of the study's wide range of animals, because birds are "just the dinosaurs that haven't gone extinct."

But Brian Enquist, a University of Arizona evolutionary biology professor and one of the authors of the initial study, cited problems with D'Emic's analysis, including the bird comparison.

"Dinosaurs were not as metabolically turbocharged as their living feathered relatives," he said. "Their closest metabolic analogues are living mesotherms -- tunas, echidnas and the like."

Found in Australia, echidnas, which look like a porcupine-anteater cross, are among the few mammals that lay eggs.

Another of the original researchers, Felisa Smith, a University of New Mexico professor, also said D'Emic's methodology was flawed. He should, for example, also have doubled the growth rates for the other animals. That would, however, have produced "no change in the overall results," she said.

The controversy might take quite a lot of work to resolve. D'Emic estimated scientists have yet to sample the bones of another 600 to 700 dinosaurs.Mary Schweitzer, curator of Vertebrate Paleontology at the North Carolina Museum of Natural Sciences, agreed more research was warranted and that failing to weigh likely seasonal variations in growth rates perhaps might have biased the original study's results.

Additionally, examining the entire skeleton of a dinosaur might reveal some surprises, as all of its bones might not grow at the same rate.

That certainly is the case in humans, Schweitzer said, estimating that at birth, an infant's head is about one-third of its entire length. But by adulthood, that ratio shrinks to around one-eighth. "Evidence suggests that 'growth rates' of bones within a single animal differ."