Dinosaurs Warm-Blooded: Cold-Blooded Dinosaurs Wouldn't Have Been Muscular Enough To Survive, Suggests Study

By iScienceTimes Staff on July 18, 2013 3:29 PM EDT

dinosaur rex
Dinosaurs were warm-blooded, suggests new research. Cold-blooded dinosaurs would not have been muscular enough to prey on mammals, the research says. (Photo: Reuters)

There's good reason to believe that dinosaurs were warm-blooded, according to a new paper by Roger Seymour of the University of Adelaide, in Australia.  

Seymour's argument hinges on the idea that if dinosaurs were cold-blooded, they wouldn't have enough muscle power to prey on other animals and to dominate the food chain.

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"Much can be learned about dinosaurs from fossils but the question of whether dinosaurs were warm-blooded or cold-blooded is still hotly debated among scientists," said Seymour.

Seymour says that the example of cold-blooded animals, like the saltwater crocodile, show that a cold-blooded dinosaur wouldn't have enough strength to take on warm-blooded mammals.

"Some point out that a large saltwater crocodile can achieve a body temperature above [86 degrees Fahrenheit] by basking in the sun, and it can maintain the high temperature overnight simply by being large and slow to change temperature," said Seymour.

Those same people, said Seymour, point out that old-blooded dinosaurs could have done the same, soaking up sun without the need to generate heat in their own cells.

But by analyzing crocodile blood and muscle lactate measurements, Seymour concluded that crocodiles, which are 50% muscle, only have about 14 percent of the muscle power of a mammal at peak exercise.  

Scale that up to the size of a dinosaur, Seymour says, and the loss of muscle power only gets larger.

"Dinosaurs dominated over mammals in terrestrial ecosystems throughout the Mesozoic. To do that they must have had more muscular power and greater endurance than a crocodile-like physiology would have allowed," he said.

Last year, a study published in Nature claimed that one of the biggest arguments for dinosaurs being cold-blooded was highly questionable. The argument revolves around the bones of dinosaurs, which show lines of arrested growth, or LAGs. LAGs were thought to be almost exclusively found in cold-blooded animals, as the lines indicate cold seasons, when a cold-blooded animal's body temperature changes--unlike warm-blooded mammals, whose temperatures remain more consistent, and thus don't have bones with LAGs.

But the Nature study claimed that it wasn't true at all that only cold-blooded animals had LAGs. The researchers found a number of warm-blooded animals that did too, and that "LAGs cannot be used as an argument that dinosaurs could not have been [warm-blooded]."

The debate over dinosaurs being warm- or cold-blooded is, of course, far from over. Seymour's findings can be found in the journal PLOS One.

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