An artist's impression of the carnivorous dinosaur, Tawa hallae, described in this week's edition of the journal Science Fossil hunters have unearthed one of the earliest known relatives of the Tyrannosaurus Rex in the U.S.
The two-legged predator Tawa hallae, was found on the Ghost Ranch in New Mexico and scientists say it has shed new light on early dinosaur evolution.
The theropod dinosuar lived 213 million years ago, while its most famous descendant - the T.Rex - did not appear until 68 million years ago.
A team led by Sterling Nesbitt from the University of Texas unearthed a number of well-preserved Tawa hallae skeletons that ranged in size from 6.6ft to 13ft long. A full grown T. Rex could reach up to 43ft in length.
The scientists are fairly confident the newly-discovered creature was a carnivore because its teeth had little serrations like a steak knife.
The finding suggests dinosaurs may have originated in what is now South America and then dispersed around the world instead of evolving in different places.
The biggest surprise came when T. hallae was compared with two other species from the same era and order of dinosaurs also found at the ranch.
All three were expected to share similar characteristics, but instead they were less like each other than they were to a known South American dinosaur.
Based on T. hallae's relationship with other dinosaurs, scientists now think early ancestors of the reptiles that came to dominate the world for 200 million years first evolved in what is now South America.
T Rex, made famous by the film Jurassic Park, was almost four times as long as its ancestor and could grow up to 43ft in lengthAt the time all the land on Earth existed as one super-continent, called Pangaea. The early dinosaurs diverged into theropods (like T. rex), long-necked four-footed sauropods (like Brachiosaurus), and ornithischians (like the three-horned Triceratops).
The creatures then dispersed more than 220 million years ago across parts of Pangaea that later broke away to become separate continents.
Dr Randall Irmis, from the Utah Museum of Natural History, who took part in the research published today in the journal Science, said: 'The discovery of multiple dinosaur species in one place that emigrated from elsewhere got us wondering whether other Late Triassic reptiles show similar patterns.
'It turns out a variety of other reptile groups made multiple trips from the northern and southern continents (then parts of Pangaea) and back again during the Late Triassic, including other dinosaurs.
'This new dinosaur Tawa hallae changes our understanding of the relationships of early dinosaurs, and provides fantastic insight into the evolution of the skeleton of the first carnivorous dinosaurs.'
During the Late Triassic there were not thought to be major physical barriers, much as large mountain ranges, to get in the way of dinosaur migration.
But this posed a puzzle, since no Triassic sauropods or ornithiscian dinosaurs have been found in North America.
'Our conclusion is that climate, possibly related to latitude, controlled the distribution of some reptile species,' said Dr Irmis.
'We think that all the major dinosaur groups had the ability to get to North America during the Late Triassic, and may have even passed through, but for some reason, only the carnivorous dinosaurs found the North American climate to be hospitable during this time.'
source: dailymail.co.uk
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