Dinosaurs were warm-blooded, new paper reports PALEONTOLOGY

This June 15, 2012, photo, shows a repaired Tyrannosaurus Rex skull at the Orton Geological Museum in Columbus, Ohio. Months after an Ohio State University student trashed the Orton Geological Museum, an artist, a curator and elementary schoolchildren are helping to piece history back together. About 175 second- and third-grade gifted students from Hilliard elementary schools did chores, held bake sales and even sold "doughnuts for dinosaurs" to raise money to help repair the museum's exhibits. (AP Photo/The Columbus Dispatch, Tom Dodge) less This June 15, 2012, photo, shows a repaired Tyrannosaurus Rex skull at the Orton Geological Museum in Columbus, Ohio. Months after an Ohio State University student trashed the Orton Geological Museum, an ... more Photo: Tom Dodge, Associated Press Photo: Tom Dodge, Associated Press Image 1 of / 1 Caption Close Dinosaurs were warm-blooded, new paper reports 1 / 1 Back to Gallery

Scientists studying the bones of living animals have found new evidence that dinosaurs were warm-blooded like modern mammals and birds - not cold-blooded reptiles, according to a Berkeley expert on the ancient creatures.

For more than 40 years, some paleontologists have argued that the dinosaurs were cold-blooded, like modern reptiles - the technical term is ectotherms - while most fossil hunters have agreed that, whether they were as large as Tyrannosaurus rex or as small as chicken-sized Velociraptor, the dinosaurs were warm-blooded - the term is endotherms.

The finding that dinosaurs could regulate their own body temperatures comes from a massive study of bones that Spanish scientists sampled in more than 100 modern ruminant animals living in 36 different climate regions of the world. They include the furry musk oxen of the High Arctic to the giraffes and antelopes of Africa, all of them living in varied climates, wet or dry, cold or hot, and all of them endothermic.

The Spanish scientists, led by Meike Köhler of the Autonomous University of Barcelona, published a detailed report on their research Wednesday in the journal Nature.

The key to the group's study are bone structures in modern animals called lines of arrested growth, or LAGs. Lines of arrested growth are formed during periods when active animals slow their growth rates - much as tree rings are formed each year.

Paleontologists have seen those LAGs in dinosaurs of all kinds. They are also in modern lizards and crocodiles that are unrelated to dinosaurs, and evolved along a line far separate from them, but are known to be cold-blooded, or ectotherms.

In the past some controversial paleontologists have cited the same arrested growth lines to argue that they proved dinosaurs were cold-blooded and had to use the environment to regulate their internal body temperature, the way cold-blooded lizards do when they bask in the sunshine to warm up.

But in his conclusive argument in Nature that accompanied the report, titled "A bone for all seasons," Kevin Padian of the UC Berkeley Museum of Paleontology noted that microscopic features of dinosaur bones show precisely the same lines of arrested development as the bones that Köhler and her colleagues studied in modern animals, which live in all the world's climates.

"The bone growth patterns of dinosaurs establishes that they grew just like large mammals do, and at comparable rates," Padian said in an e-mail Wednesday. "So their physiology could not have been like lizards and crocodiles, which grow much more slowly and whose bones look very different inside."

Padian has long argued that warm-blooded and cold-blooded animals have formed a "continuum" in evolution.

"Actually there never was any evidence that dinosaurs were ectotherms," he said Wednesday. "It was just sort of like, well, dinosaurs are reptiles, and living reptiles are cold-blooded, so dinosaurs were cold-blooded too."