Dinosaurs Had Middling Metabolisms: T. Rex and Kin Straddled Line between Cold- and Warm-Blooded

By Rosen, Meghan | Science News, July 12, 2014 | Go to article overview

Dinosaurs Had Middling Metabolisms: T. Rex and Kin Straddled Line between Cold- and Warm-Blooded


Rosen, Meghan, Science News


Dinosaurs weren't quite like cold-blooded reptiles, but they weren't like warm-blooded birds either. Instead, they fell smack-dab in the middle. Comparisons with modern animals reveal that dinosaurs' metabolisms probably resembled those of great white sharks, researchers report in the June 13 Science.

The findings offer new clues into how the animals lived and also rekindle a long-standing debate. "This paper will make us go back to the drawing board," says paleobiologist Martin Sander of the University of Bonn in Germany.

For years, paleontologists assumed that dinosaurs most resembled modern reptiles and other cold-blooded creatures, or ectotherms: slow-growing, low-energy sluggards that bask in sunlight for heat and don't need much food. "When I was a kid, dinosaurs were just scaled-up, tail-dragging reptilian brutes," says Gregory Erickson, a paleobiologist at Florida State University in Tallahassee.

The field took a U-turn in the 1960s, he says, when researchers started to find similarities between dinosaurs and modern birds. Over the next few decades, most paleontologists came to think of dinosaurs as more birdlike: warm-blooded animals, or endotherms, that grew quickly, expended lots of energy and regulated their body heat internally. That thinking inspired popular depictions such as the speedy beasts of Jurassic Park.

But trying to shoehorn dinosaurs into one of two camps might be too simplistic, says John Grady, a paleoecologist at the University of New Mexico in Albuquerque.

Previous work had hinted that the animals might not sort so cleanly into either group. So Grady and colleagues designed a massive study to pinpoint dinosaurs' place on the spectrum of cold- and warm-blooded life.

His team tabulated the growth rates and energy use, or metabolism, of 353 modern animal species. The census ran the gamut from slow-growing, low-metabolism crocodiles to fast-growing, high-metabolism ostriches. Then the researchers capitalized on other paleontologists' careful analyses of dinosaur bones to collect the growth rates of 21 dinosaurs, including Tyrannosaurus and Apatosaurus. …

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