Dinosaurs may have been warm-blooded, after all

You may not know this, but the warm and/or cold nature of dinosaurs is … hotly contested. A study last year put dinosaurs solidly in-between cold-blooded reptiles and warm-blooded modern mammals, metabolically speaking. But by analyzing the same data, Stony Brook University Professor Michael D’Emic came to a different conclusion: Dinosaurs weren’t wishy-washy when it came to body temperature regulation, they were just plain warm-blooded. His findings will be published Friday in Science.

“The 2014 paper is still really important,” D’Emic said, even if his analysis is the correct conclusion. “It’s the largest study of its kind so far, and they compiled tons of data from living animals to compare them to the dinosaur species that have been analyzed.”

Of the hundreds of known dino species, just a couple dozen have been studied in this way — looking at microscopic signs of growth on their bones.

The 2014 study suggested that dinosaurs probably warmed themselves up to some degree — enough to make their nerves and muscles quicker, turning them into speedy predators — but not enough to regulate body temperature all the time. The compromise would allow them to make quick sprints but live slow lives. Based on their analysis, the researchers estimated that a T. rex with a warm-blooded metabolism as we know it would have to eat 24/7 in order to survive.

In his analysis of the same data, D’Emic argues that the varied growth rate of dinosaurs needs to be taken into account.

“We looked at growth lines in bones,” he said, comparing them to tree lines. “They’re laid down incrementally. During the summer, when there’s lots of food, the animal would lay down bone. That would slow or even pause in the winter. So you can see how they grew from year to year.”

Based on the speed of growth he sees, he suggests that a mammalian metabolism is the most likely culprit.

But D’Emic knows the suggestion is far from an end to the debate.

“We know so little about how dinosaurs grew overall, because we’ve studied so few of them this way,” he said. “My study argues that the dinosaurs I’m looking at had mammal-like metabolisms and growth rates. But that certainly doesn’t mean they all did.”