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Dinosaur blood temperature debate resolved

A debate has raged about the metabolism and blood temperatures of dinosaurs since the first dinosaur remains were discovered. Some scientists claim dinosaurs were cold-blooded like reptiles and some researchers claim dinosaurs were warm-blooded based on more recent feathered dinosaur discoveries. John Grady, a biologist at the University of New Mexico in Albuquerque, and colleagues reported research that may settle the debate in the June 12, 2014, edition of the journal Science.

A costumed dinosaur, Baby T, from 'Walking with Dinosaurs' throws out the first pitch before a baseball game between the Kansas City Royals and the San Diego Padres at Petco Park May 7, 2014, in San Diego, California.
Photo by Denis Poroy/Getty Images

Grady concludes that dinosaurs were neither exclusively cold-blooded like reptiles nor completely warm-blooded like birds and mammals. The fact that dinosaurs lived on Earth for 200 million years and no evidence of hibernation or estivation like reptiles has ever been discovered is one telling point from the fossil record. The fact that dinosaurs changed location as a result of changing climates also argues for a middle of the road metabolism in dinosaurs.

Grady compared the growth rate of 381 living animal species and 21 dinosaurs. The most telling measure of comparison was counting the growth rings in dinosaur bones. The size of dinosaur bones was also a factor in the analysis. The researchers found that mammals grow about 10 times as fast as dinosaurs because mammal metabolism is 10 times as fast as dinosaurs. Mammals offer a broad range of metabolism that varies with life on land or in the water as well as climate and food sources.

Blood temperature and metabolic rate in dinosaurs were a function of size and climate. The larger dinosaurs required a higher blood temperature in order to support their mass and the rate of growth seen in the fossil record. Predatory dinosaurs needed a higher blood temperature and higher rate of metabolism to supply the energy necessary for high-speed hunting.

The researchers conclude that blood temperature in dinosaurs was species dependent and time dependent. The last living dinosaurs probably had higher blood temperatures because the Earth’s climate had changed and the animal’s had evolved. This study is proposed as a resolution of a long argument about blood temperature and metabolism in dinosaurs.