Scientists Say Most Dinosaurs Were Mesothermic

Posted on June 13, 2014

Scientists at the University of New Mexico (UNM) say most dinosaurs were mesothermic, a middle path between warm-blooded and cold-blooded. Some of the few mesothermic creatures today include great white sharks, tuna, leatherback sea turtles and echidnas. The chart above shows growth rates across an evolutionary tree, with dinosaur growth ratings being closest to living mesotherms.

The researchers analyzed a database of animal growth and energy use developed by John Grady, a graduate student at UNM and lead author of the research. The researchers found that animals that grow faster, not only require more energy, but have higher body temperatures. Using growth estimates made by paleontologists for extinct dinosaurs, the researchers calculated dinosaur metabolic rates. The researchers found that dinosaurs intermediate between modern mammals and reptiles. They found that feathered dinosaurs and primitive birds grew distinctly slower than their descendants, modern birds.

Grady says in a statement, "Archaeopteryx, the first bird, took two years to reach maturity. But, a red-tailed hawk, which is about the same size, only takes 6 weeks. While dinosaurs didn't grow as fast as modern birds or mammals, they did grow significantly faster than modern reptiles. This higher energy use probably increased speed and performance. Mesothermic dinsoaurs were likely faster predators or better able to flee from danger than the large reptiles found earlier in during the Mesozoic."

The researchers say mesothermy likely helped dinosaurs become both ecologically dominant and enormous.

UNM Professor Felisa Smith says, "A lion the size of a T-Rex, while a frightening thought, would quickly starve to death because it would be so hard to find enough food."

A research paper on the study was published here in the journal, Science.

DINOSAURS