For 130 years, dinosaurs have been classified as either bird - or reptile-hipped -- the first and all-important split in the trunk of an intricate family tree. However, a "revolutionary" study threatens to upend what has long been taken as gospel by preschoolers and paleontologists alike -- that a dinosaur's evolutionary history can be determined by the shape of its pelvis. "Our study overturns 130 years of dogma," said study co-author Paul Barrett of the Natural History Museum.<br /><br />"Our analysis suggests that animals like T. rex were actually more closely related to Stegosaurus" -- dinos once thought to be firmly on either side of the hip divide.<br /><br />A new dinosaur evolutionary tree, published in the journal Nature, proposes two new base groups, in which bird- and reptile-hipped lizards are now mixed.<br /><br />It also suggests that dinosaurs arose around 247 million years ago -- some 10 million years earlier than thought -- and in the northern hemisphere rather than the south.<br /><br />Barrett and a team examined a large sample of features of very early dinosaurs to learn more about the original, common ancestor and its first offshoots.<br /><br />The first dinosaur, they concluded, was likely a small omnivore that walked on its hind legs and had grasping hands. These aspects have been the subject of much scientific debate.<br /><br />But the most controversial finding concerns what happened next.<br /><br />Dinosaurs split into two main groups, but quite unlike those assumed until now, said the team.<br /><br />Birds find a home-<br /><br />Since the Victorian era, dinosaurs have been split into two categories: The bird-hipped (Ornithischia) and reptile-hipped (Saurischia).<br /><br />The Saurischia group was sub-divided into bipedal carnivores called theropods, which included the likes of Tyrannosaurus Rex and Velociraptor, and the massive, long-necked sauropods such as Brontosaurus.<br /><br />But under the new classification, bird-hipped dinos such as the three-horned Triceratops and armored Stegosaurus no longer comprise one of the two basal categories. <br /><br />Instead, they are sub-divided into a completely new category, called Ornithoscelida, along with theropods which were removed from under the reptile-hipped Saurischia.<br /><br />"We have... pulled Theropods out, but the old Saurischia limps on," as one of the two foundational categories, the study's lead author Matthew Baron from the University of Cambridge told AFP.<br /><br />The new Ornithoscelida category, he proposed, can be described as "bird-limbed". Its members share common hind-limb as well as skull features.<br /><br />"We propose that the dinosaur family tree actually looks very different from the version that has been accepted by scientists for the last 130 years," said Baron.<br /><br />For the first time, the ancestors of modern birds, reptile-hipped theropods, are grouped with bird-hipped dinosaurs into a single category.<br /><br />If the conclusions are correct, said Baron's colleague David Norman, "All the major textbooks covering the topic of the evolution of the vertebrates will need to be re-written."<br />
