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Dinosaurs Not Cold-Blooded in Theory That Flips Old View

Dinosaurs Weren’t Cold-Blooded in Theory That Flips Old Beliefs
Three Utahraptors hunt as a pack in a scene from "Walking With Dinosaurs- the Arena Spectacular" in Omaha, Nebraska. Photographer: Joan Marcus/Walking With Dinosaurs- the Arena Spectacular via Bloomberg

A closer look at modern-day mammals has led scientists to conclude that dinosaurs were warm-blooded, in a serendipitous finding that demolishes the main argument that the creatures were giant cold-blooded reptiles.

In a study that started as a way of learning more about the bones of mammals, researchers found that the same skeletal markings seen on dinosaurs also appeared on large ruminant animals, such as deer. Called lines of arrested growth or LAGs, the markers indicate rain and supply of food and water, rather than external temperature, according to the research published today in the journal Nature.

Some scientists theorized that dinosaurs didn’t generate their own internal heat and pointed to LAGs in bones as evidence, according to the study’s background information. This latest research adds evidence that the giant creatures roaming the earth millions of years ago weren’t cold-blooded, but rather warm-blooded like birds or mammals.

“There’s never been any evidence at all that dinosaurs were cold-blooded,” said Kevin Padian, a professor of integrative biology at the University of California, Berkeley, and author of an accompanying article, in a telephone interview. “Birds evolved from reptiles and so at some point along the way, warm-bloodedness evolved.”

Warm-bloodedness and cold-bloodedness are inexact ways of thinking about body heat, said Padian, who is also the curator of paleontology at the University of California Museum of Paleontology. Endothermic animals like birds and mammals generate their own heat while ectothermic animals like current reptiles rely on the environment to generate heat, he said. What’s more, some animals are better at maintaining a constant internal body temperature, while others aren’t.

Previous Research

A study published in the journal Science last year suggested that a nearly intact heart from a small plant-eating dinosaur had a structure more similar to that of a mammal or bird.

Once the researchers discovered the LAGs in mammals, they published today’s paper because they realized it could have important implications for dinosaurs, said study author Meike Kohler, a researcher at the Institut Catala de Paleontologia Miquel Crusafont at the Autonomous University of Barcelona, Spain.

Now that LAGs are known in mammals, scientists will be able to use them the same way as tree rings or growth markers to study the conditions under which the animals grew, Kohler said in a telephone interview. Looking at how animals were influenced by climate and extension events will help future research. What’s more, they now provide a way to tell the longevity and age of sexual maturity in samples, she said.

“This is an important set of demographic data,” Kohler said in a telephone interview. “It will likely be valuable in conservation biology.”

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