Researchers meditate the evolutionary family tree diagram of tyrannosauroids reveal thatTyrannosaurus rexmay have migrate from Asia to North America , where the mintage took over immediately . The work , print inScientific Reportslast month , also suggest that the short - armed , deeply - skulled consistency plan of the stupendous bone cruncher evolved in a piecemeal fashion .
The 13 - meter - long ( 43 feet)T. rexreigned at the top of the food for thought chain in North America at the end of the Cretaceous some 66 million years ago . The species was one of the last survivor of a major carnivorous group address the tyrannosauroids , which initiate 100 million yr before . These dinosaur used to be widely distribute , small , and ecologically marginal . In fact , it was n’t until shortly before the last - Cretaceous asteroid coin thatT. rexand its closest kinsperson ( foretell the tyrannosaurids ) became enormous .
In the last few years , many newfangled species have been divulge , raising new questions about the origin and evolutionary relationships ( or phylogenetics ) of the group . To fabricate an updated organic evolution , University of Edinburgh ’s Stephen Brusatte and Thomas Carr of Carthage College studied 366 anatomic characters of 28 tyrannosauroids .
They discovered that the famousT. rexbody design did n’t develop rapidly . Features that enabled potent and stronger bite force develop incrementally , and cranial ornamentation ( such as skull crest ) gradually became more luxuriant .
At about 9 meters ( 30 foot ) long , YutyrannusandSinotyrannusare early example of large eubstance . They had shallower skull and modest jaw muscles thanT. rex , butYutyrannushad a with child , three - fingered arm , not a withered two - fingered forearm . So while early other Cretaceous tyrannosauroids were capable of evolving passably large sizing during the mediate portion of their evolutionary history , colossal size – 1.4 tonnes ( 1.5 gobs ) or more – add up much later , about 80 million year ago . funnily enough , the late former CretaceousXiongguanlong – the early to present a broad U - wrought snout and other familiar features of the jumbo death - Cretaceous tyrannosaurids – showed no sign of developing gigantism . Its body mess was a meek 170 kilogram ( 375 pound ) .
Furthermore , the researchers found no clear division between northerly and southern species in western North America , called Laramidia . ( The east and west coasts would have been branch by a seaway . ) This suggests that tyrannosaurids were n’t provincial ; rather , they were dynamic and capable of spreading around .
And at long last , the squad reveal thatT. rexmay have been an Asiatic migrator to North America . During the last 20 million years of the Cretaceous , the large - bodied meat eaters live on both continents . The team nestedTyrannosauruswithin a submarine sandwich - lineage that includes two Asiatic tyrannosaurids : TarbosaurusandZhuchengtyrannus . The three were very standardised . It ’s possible that the two Asian descent disseminate from North America ; it ’s every bit possible thatTyrannosaurusoriginated in Asia , then immigrated to North America .
“ In other Holy Scripture , it may be thatT. rexwas an invasive migrant species that distribute across Laramidia , ” the authors compose . This may excuse why there was just one large tyrannosaurid in North America during the tardy Late Cretaceous , when there were multiple over in Asia . T. rexlikely pushed others out as presently as it arrived .
