Dinosaurs were warm-blooded like mammals, not cold-blooded like reptiles as previously thought, says a biologist from the University of Adelaide, Australia.
This image shows different dinosaur species, left to right: Chasmosaurus belli, Lambeosaurus lambei, Styracosaurus albertensis, Euoplocephalus tutus, Prosaurolophus maximus, Panoplosaurus mirus and a herd of S. albertensis in the background (© J.T. Csotonyi)
Prof Roger Seymour argues that cold-blooded dinosaurs would not have had the required muscular power to prey on other animals and dominate over mammals as they did throughout the Mesozoic period.
The biologist says that 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. Some point out that a large saltwater crocodile can achieve a body temperature above 30 degrees Celsius by basking in the sun, and it can maintain the high temperature overnight simply by being large and slow to change temperature.
“They say that large, cold-blooded dinosaurs could have done the same and enjoyed a warm body temperature without the need to generate the heat in their own cells through burning food energy like warm-blooded animals.”
The scientist asks how much muscular power could be produced by a crocodile-like dinosaur compared to a mammal-like dinosaur of the same size. Saltwater crocodiles reach over a tone in weight and, being about 50 per cent muscle, have a reputation for being extremely powerful animals. But drawing from blood and muscle lactate measurements, Prof Seymour shows that a 200 kg crocodile can produce only about 14 per cent of the muscular power of a mammal at peak exercise, and this fraction seems to decrease at larger body sizes.
“The results further show that cold-blooded crocodiles lack not only the absolute power for exercise, but also the endurance, that are evident in warm-blooded mammals. So, despite the impression that saltwater crocodiles are extremely powerful animals, a crocodile-like dinosaur could not compete well against a mammal-like dinosaur of the same size.”
“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,” concludes Prof Seymour, who presented his findings in the open-access journal PLoS ONE.
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Bibliographic information: Seymour RS. 2013. Maximal Aerobic and Anaerobic Power Generation in Large Crocodiles versus Mammals: Implications for Dinosaur Gigantothermy. PLoS ONE 8 (7): e69361; doi: 10.1371/journal.pone.0069361
