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.
On Wednesday, a “revolutionary” study threatened 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,” coauthor Paul Barrett of Britain’s Natural History Museum said.
“Our analysis suggests that animals like T. rex were actually more closely related to Stegosaurus” — dinosaurs once thought to be firmly on either side of the hip divide, he said.
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.
It also suggests that dinosaurs arose about 247 million years ago — about 10 million years earlier than thought — and in the northern hemisphere rather than the south.
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.
The first dinosaur was likely a small omnivore that walked on its hind legs and had grasping hands, they said.
These aspects have been the subject of much scientific debate.
However, the most controversial finding concerns what happened next.
Dinosaurs split into two main groups, but quite unlike those assumed until now, the team said.
Since the Victorian era, dinosaurs have been split into two categories: bird-hipped (Ornithischia) and reptile-hipped (Saurischia).
The Saurischia group was subdivided into bipedal carnivores called theropods and the massive, long-necked sauropods.
However, under the new classification, bird-hipped dinosaurs such as the three-horned Triceratops and armored Stegosaurus no longer comprise one of the two basal categories.
Instead, they are subdivided into a completely new category, called Ornithoscelida, along with theropods, which were removed from under the reptile-hipped Saurischia.
“We have ... pulled theropods out, but the old Saurischia limps on,” as one of the two foundational categories, said the study’s lead author, Matthew Baron, from the University of Cambridge.
The new Ornithoscelida category can be described as “bird-limbed,” he said.
Its members share common hind-limb as well as skull features.
If the conclusions are correct, “all the major textbooks covering the topic of the evolution of the vertebrates will need to be rewritten,” said Baron’s colleague, David Norman.
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