Just One Animal Today Has Teeth Like T. rex

T. rex and other big dinosaurs had teeth that were specialized for tearing through flesh and bone -- only one living animal has similar tooth structure. Can you guess which?

Tyrannosaurus rex and other large meat-loving dinosaurs had deeply serrated teeth that let them tear through the flesh and bone of victims.

Only one animal living today has this same tooth structure, according to new research, published in the journal Scientific Reports. The Komodo dragon, which is the world's largest lizard, holds that distinction.

"What is so fascinating to me is that all animal teeth are made from the same building blocks, but the way the blocks fit together to form the structure of the tooth greatly affects how that animal processes food," project leader Kirstin Brink of the University of Toronto Mississauga's Department of Biology, said in a press release.

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Brink and her colleagues used both a scanning electron microscope and a synchrotron, which can identify a substance's chemical composition, to analyze tooth slices from eight meat-eating dinosaurs, such as T. rex, Allosaurus, Coelophysis and Gorgosaurus.

The investigations revealed that the serrations on the teeth of these bloodthirsty predators were supported by tissues inside of each tooth. The arrangement of these tissues reinforced the serrations all the more, making the teeth more efficient at biting through bones and ripping flesh.

As a result, it was a dinosaur-eat-dinosaur world, since the strong teeth and other adaptations allowed these now-extinct animals to take down very large prey. Before carnivorous dinos died out (dinosaurs that were not birds, that is), they prospered for about 165 million years as the planet's top terrestrial predators.

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Komodo dragons, which are native to Indonesia, can kill large prey too, including humans and 1,200-pound water buffalos. Komodo dragons also produce a venom that can prevent their victim's blood from clotting. Before the venom was discovered by scientists, animal experts used to think that bacteria harbored in the mouths of Komodo dragons helped to kill prey.

Brink and her team determined that, in the dinosaur teeth, the unique arrangement of interior tooth tissues did not develop in response to the carnivores chewing hard materials. They came to that conclusion after examining samples of dinosaur teeth that had not yet broken through the gums when the animals died. They also looked at samples from mature dinosaur teeth.

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"What is startling and amazing about this work is that Kirstin was able to take teeth with these steak knife-like serrations and find a way to make cuts to obtain sections along the cutting edge of these teeth," said co-author Robert Reisz. "If you don't cut them right, you don't get the information.

He added, "This brought about a developmental explanation for the tooth formation; the serrations are even more spectacular and permanent."

A recreation of Gorgosaurus feeding on a young Corythosaurus in Alberta, Canada, 75 million years ago.

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."

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"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."

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"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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