Dinosaurs were Warm-Blooded: Study

Dinosaurs are generally thought of as cold-blooded animals like reptiles. However, a new study from Australia provides evidence that dinosaurs were warm blood animals just like mammals and birds.

The main argument of the latest study is that had dinosaurs been cold-blooded, they wouldn't have the muscle power to catch other animals and dominate over mammals during the Mesozoic period.

The idea that dinosaurs could have been warm-blooded was proposed by Robert Bakker and John Ostrom in 1960s. A study supporting this hypothesis was published last year, where a team of researchers had studied growth lines on the dinosaurs' bones and found that dinosaurs had high metabolism rates and high growth rates, which meant they were warm-blooded.

The present study was conducted by Professor Roger Seymour of the University of Adelaide School of Earth and Environmental Sciences and colleagues from Monash University, University of California and Wildlife Management International in the Northern Territory.

"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 Professor Seymour. "Some point out that a large saltwater crocodile can achieve a body temperature above 30°C by basking in the sun, and it can maintain the high temperature overnight simply by being large and slow to change temperature.

The assumption is that dinosaurs might have done the same thing without spending energy to keep themselves warm, Seymor added, according to a news release.

"But how much power could a crocodile-like dinosaur produce compared with a dinosaur that has warm blood, when they both are of equal size?," is what the researchers wanted to know in the present study.

Crocodiles are big, especially the saltwater ones that can reach up to a ton, and being about 50 percent muscle, can generate enough power to rip off its warm blooded prey.

However, there is a catch here; the larger the cold blooded creature gets, the lower its muscle power gets. For example, a 400 pound crocodile can generate about 14 percent of the power generated by a mammal of the same size during peak exercise. The study was based on blood and muscle lactate measurements of warm and cold-blooded animals.

Seymor added that cold-blooded animals the size of a dinosaur wouldn't even have the endurance to compete with mammals of the Mesozoic period.

"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.

The study is published in the journal PLOS One.