It has been a long-standing question whether dinosaurs were warm-blooded like mammals (‘endotherms’) or cold- blooded like reptiles (‘ectotherms’)—and there was scant evidence to prove one or the other. Now, scientists from the University of New Mexico (UNM) say they may have solved the puzzle: dinosaurs were somewhere in-between. The study is published in this week’s issue of the journal Science.
Dinosaurs dominated the world of land animals for millenia before becoming extinct 65 million years ago in a cataclysmic event, most likely a massive asteroid strike.
According to lead researcher and graduate student John Grady, most dinosaurs followed an intermediate metabolic path between being warm-blooded or cold-blooded.
“Most dinosaurs were probably mesotherms,” Grady said in a UNM statement. “A thermally intermediate strategy that only a few species—such as egg laying echidnas or great white sharks—use today.”
The research team explained on Thursday that they determined the metabolism of 21 species of dinosaurs by relying on one basic fact: warm-blooded creatures grow faster than cold-blooded ones. They used a formula based on their body mass as revealed by the size of their thigh bones and determined the dinosaurs’ growth rates by looking at growth rings in the fossilized bones—similar to telling the age of a tree by looking at tree rings.
Among the dinosaurs that Grady and his colleagues evaluated were the fierce predators T-rex and Allosaurus, long-necked Apatosaurus, duckbilled Tenontosaurus along with a range of mammals, birds, bony fish, sharks, lizards, snakes and crocodiles, according to a report by Reuters.
The ancient bones revealed that dinosaurs grew faster than reptiles and slower than mammals—pointing to a metabolism that was neither warm-blooded or cold-blooded. And, as Grady observed, an intermediate metabolism “seemed to work out very well for them.”
Evolving a mesothermic metabolism may have helped dinosaurs to grow much larger than was possible for any mammal. Warm-blooded animals have to spend a lot of their time eating to maintain their high metabolic rate. This makes it “doubtful that a lion the size of T. Rex could eat enough to survive,” Grady told Reuters.
Read more: http://www.sciencerecorder.com/news/scientists-uncover-the-in-between-goldilocks-nature-of-dinosaur-blood/#ixzz34Te579W4