Animals

Dinosaurs May Have Been Warm-Blooded

Dinosaurs might have been more like us than previously thought, claims a new study.

Dinosaurs were warm-blooded animals that had many traits in common with mammals, finds controversial new research.

The study, published in the journal Science, counters other popular theories, which say that dinosaurs were either cold-blooded and reptile-like, or occupied a unique intermediate category of animals that were neither fully cold nor warm-blooded.

"Upon re-analysis, it was apparent that dinosaurs weren't just somewhat like living mammals in their physiology - they fit right within our understanding of what it means to be a ‘warm-blooded' mammal," author Michael D'Emic, a Stony Brook University paleontologist, said in a press release.

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The "re-analysis" refers to D'Emic's work revisiting yet another Science paper, published last year, which compiled a huge dataset on growth and metabolism of hundreds of living animals. D'Emic admits that this dataset was "remarkable" and "unprecedented."

Yet, that earlier study found that dinosaurs would have fit into the intermediate category between ectothermic (cold-blooded, with body temperature controlled largely by the surrounding environment) and endothermic (warm-blooded, like us).

D'Emic looked at that study again, focusing on two primary aspects.

First, the original study had scaled yearly growth rates to daily ones in order to standardize comparisons.

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"This is problematic," D'Emic said, "because many animals do not grow continuously throughout the year, generally slowing or pausing growth during colder, drier, or otherwise more stressful seasons. Therefore, the previous study underestimated dinosaur growth rates by failing to account for their uneven growth. Like most animals, dinosaurs slowed or paused their growth annually, as shown by rings in their bones analogous to tree rings."

He added that very stressful or seasonal environments can also impact growth, and would have really affected dinosaurs. He believes that these factors were underestimated in the earlier study.

The second aspect of his re-analysis took into account the widely held view that all dinosaurs did not become extinct: some evolved to become birds. Today's birds are warm-blooded, so he argues that dinosaurs must have been this way too.

"Separating what we commonly think of as 'dinosaurs' from birds in a statistical analysis is generally inappropriate, because birds are dinosaurs–they're just the dinosaurs that haven't gone extinct," he explained.

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If D'Emic's theory about warm-blooded dinosaurs holds, then this would lead to still more re-evaluation of other data on things like the big sails and head ornaments on some dinosaurs. Certain past studies have linked these to body temperature regulation. If they didn't serve that function, then perhaps they were used more for flashy mating displays or other types of visual communication.

Holly Woodward, an assistant professor in the Center for Health Sciences at Oklahoma State University, supports re-examining prior studies, even those that appear seamless.

As she said, "D'Emic's study reveals how important access to the data behind published results is for hypothesis testing and advancing our understanding of dinosaur growth dynamics."

For now, though, the debate rages on among paleontologists as to whether or not dinosaurs (before the emergence of birds) were warm blooded or not.

There's a surprising human benefit to such research, D'Emic shared. His research on when why, and how pauses or slowdowns in growth are recorded in bones could have implications for treating human bone diseases, such as osteoporosis.

Recreation of Velociraptor at Dinosaur Adventure Park.

Paleontologists have just assembled the most comprehensive family tree of meat-eating dinosaurs. Published in the journal Current Biology, the family tree reveals how diverse carnivorous dinosaurs were and how birds eventually evolved from them. Tyrannosaurs, including

Tyrannosaurus rex

, are one key group on the meat-loving dino family tree. Lead author Steve Brusatte of the University of Edinburgh's School of GeoSciences told Discovery News, "The most iconic dinosaurs of all, tyrannosaurs were more than just the 13-meter-long (nearly 43 feet long), 5-ton monster predator

T. rex

." "Tyrannosaurs were an ancient group that originated more than 100 million years before

T. rex

, and for almost all of their evolutionary history they were small carnivores not much bigger than a human in size."

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"Some of the rarest theropods (two-legged carnivorous dinos) of all, compsognathids are represented by about half a dozen species," Brusatte said. "They were small, sleek meat-eaters which ate small prey like lizards." One of the more recent finds, Juravenator from Germany, is known from a nearly complete fossil.

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Ornithomimosaurs were theropods called "ostrich mimic" dinosaurs -- for a reason. "Like living ostriches, they could run fast on their long legs and used their sharp, toothless beaks to eat a varied diet of small prey, plants, and perhaps even small shrimps in the water just like living flamingos," Brusatte explained. "A recent find in Canada showed that not only were ornithomimosaurs feathered, but they also had complex feathers on their arms that would have formed something of a wing, although they couldn't fly."

Brusatte describes therizinosaurs as "perhaps the weirdest theropods of all." "These were big, bulky, cumbersome dinosaurs that ate plants. They had fat barrel-shaped chests, stocky legs, and big claws on their arms," Brusatte said. For many years paleontologists argued about which group this dinosaur belonged to, only recently settling on theropods. This means they were fairly closely related to birds, despite their weird anatomy.

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Alvarezsaurs were among the smallest dinosaurs of all, measuring just a few feet long and weighing less than 5 kilograms (10 pounds). "Some of them had only a single functional finger on their hand, which they probably used to prod deep into the nests of bugs, which were one of their main food sources," Brusatte said.

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Oviraptorosaurs, were a group of small omnivores that were lightweight, lacked teeth and had tall, hollow crests on their skulls. The recently discovered Anzu -- the so-called "

chicken from hell

" -- came by its nickname honestly. It towered more than five feet tall, weighed more than 400 pounds, and was covered in a coat of feathers.

"Troodontids were probably the smartest dinosaurs of all, as they had the largest brains relative to their body size of any dinosaur group," Brusatte said. "Most troodontids were small, fast-running dinosaurs that probably ate both meat and plants." Among the most recently discovered of this group are the small, feathered Anchiornis and Xiaotingia, which lived in China about 160 million years ago. "They look eerily similar to birds, so much so that some researchers think they could be primitive birds rather than troodontids with wings and feathers," Brusatte said.

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Dromaeosaurids were "raptor dinosaurs" that include Velociraptor from "Jurassic Park" fame. These dinosaurs were pack hunters who wielded a sharp, hyper-extendable "killer claw" on their second toe. "One of the most recently discovered dromaeosaurids is Balaur, a poodle-sized terror from Romania which had not one, but two 'killer claws' on each foot."

Velociraptor Inspires Fast Running Robot

"The oldest birds, like Archaeopteryx that lived 150 million years ago in Germany, are very hard to distinguish from their closest dinosaurian relatives," Brusatte said. "Unlike living birds, they had teeth, sharp claws on their wings, and long tails." "Over the past two decades," he continued, "over 50 new species of Mesozoic birds have been discovered in northeastern China, in the same rock units as the famous 'feathered dinosaurs.' So many birds are preserved here because entire ecosystems were buried by volcanic eruptions, turning animals to stone like a dinosaur version of Pompeii."

Tiny Feathered Dinosaur Found

"The 10,000 species of birds that live today -- from hummingbirds to ostriches -- are modern dinosaurs," Brusatte said. "They are dinosaurs in the same way that humans are mammals. The classic body plan of living birds -- feathers, wings, wishbones, air sacs extending into hollow bones -- did not evolve suddenly but was gradually assembled over tens of millions of years of evolution. But, when this body plan finally came together completely, it unlocked great evolutionary potential that allowed birds to evolve at a super-charged rate." "They underwent a burst of evolution early in their history, which eventually led to the 10,000 species alive today -- more than twice the number of mammals."

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