, king of the dinosaur age, wasn't a North American native as many experts had previously thought, a new study suggests.
Instead, the giant tyrannosaur was likely an invasive species from Asia that dispersed into western North America once the opportunity presented itself, paleontologists said.
"It's possible that T. rex was an immigrant species from Asia," said study co-researcher Steve Brusatte, a paleontologist at the University of Edinburgh in Scotland. But he cautioned that the finding isn't necessarily a "slam dunk," and that more research is needed to say for sure. [Gory Guts: See Photos of a T. Rex Autopsy]
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T. rex is one of the biggest meat eaters ever to live on land, but relatively little is known about its family tree. In a study published earlier this month, Brusatte and Thomas Carr, an associate professor of biology at Carthage College in Wisconsin, analyzed 28 different tyrannosaur species and constructed a family tree, noting approximately when and where each species lived.
Fossil evidence is lacking, but researchers suspect that the predecessors of tyrannosaurs lived on the supercontinent Pangaea, which began to break up about 200 million years ago, during the Triassic period. This would explain why tyrannosaurs fossils have been found on different continents, including Asia, western North America (called Laramidia at the time), eastern North America (Appalachia) and Europe, Carr said.
As time went on, the tyrannosaurs evolved in their respective places, meaning that the tyrannosaurs in Asia grew to look different than the ones in North America. But, around 67 million years ago, the seaway between Asia and North America went down, leaving a land bridge between the two continents, Carr said.
Perhaps T. rex crossed this route into North America, Carr said. Researchers have uncovered countless T. rex fossils in western North America, but a careful analysis of T. rex‘s skeletal features suggests that it is Asian in origin, the paleontologists found.
In fact, T. rex is closely related to two Asian tyrannosaurs, Tarbosaurus and Zhuchengtyrannus, the researchers found.
"Tarbosaurus is the Asian version of T. rex," Brusatte told Live Science in an email. "Or, you could say that T. rex is the North American version of Tarbosaurus. They are so similar in terms of their monstrous size, their proportions, their massive jaw muscles and thick teeth and even many minutiae of their skull bones."
Zhuchengtyrannus is also similar to T. rex, though it's more distantly related, Brusatte and Carr said.
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Asian invasion T. rex lived from about 67 million to 65 million years ago, going extinct when a 6-mile-long (10 kilometers) asteroid slammed into Earth and killed the nonavian dinosaurs.
During that time, the 7-ton (6.3 metric tons) T. rex monster spread from modern-day Alberta to Texas. (A giant seaway in the middle of North America prevented T. rex from reaching the East Coast, the researchers said.) Before T. rex invaded North America, presumably from Asia, other tyrannosaurs lived in western North America, but they disappeared shortly after T. rex came onto the scene.
It's unclear why these large tyrannosaurs went extinct, but T. rex may have played a role in their demise, the researchers said. [Photos: The Near-Complete Wankel T. Rex]
"Regardless of where T. rex comes from, when it enters the fossil record, it seems to take over immediately, like an invasive species," Brusette said. "It rose to the top of the food chain and elbowed out all competitors - or perhaps I should say outmuscled them, as their pathetic little arms didn't have very big elbows."
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The new finding contradicts earlier studies, some of which say that T. rex is the culmination of tens of millions of years of dinosaur evolution within North America, Brusatte said.
"This also is a good example of how different family trees can imply different things about evolution," Brusatte said. "This is why we spend so much time building family trees for fossil groups: They tell us how different species are related to each other, which then allows us to tease out their evolutionary stories, the same way constructing genealogies for our own families tells us how our ancestors led to us."
The study was published online Feb. 2 in the journal Scientific Reports.
Original article on Live Science.
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T. rex may have roamed beyond its native land.
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."
"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.
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.
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.
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 "
" -- 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.
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."
"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."
"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."