Dinosaur family tree may be completely redrawn

Tyrannosaurus rexTyrannosaurus rexFor more than a century, dinosaurs have been classified into two basic groups. But now a group of researchers have discovered evidence that, if proved correct, could mean a fundamental redrawing of the dinosaur family tree. Their research shows that the meat-eating dinosaurs, such as Tyrannosaurus rex and Velociraptor, could have been wrongly classified. Re-jigging the family tree also means re-assessing what the ancestor of all dinosaurs looked like and where it came from. It turns out that a little-known, cat-sized creature found in Scotland might be the closest to this ancestral dinosaur we know. The analysis has already sparked controversy in the world of palaeontology.

Saltopus (Nobu Tamura)Saltopus (Nobu Tamura)Until now, it was thought that the first dinosaurs emerged around 237 million years ago in the southern hemisphere. The evidence is based on fossils found in South America and Africa. However, the latest study identifies Saltopus, a small Scottish reptile (it is not certain whether Saltopus was a true dinosaur) as the closest thing to the common ancestor of all dinosaurs. It is therefore possible that the earliest dinosaurs originated in Britain about 245 million years ago.

T. rex hip bone, left side (Ballista)T. rex hip bone, left side (Ballista)Scientists have traditionally placed dinosaur species into two distinct categories: Saurischia and Ornithischia. The classification, originally made about 130 years ago, is based on the pattern of hip bones displaying either a lizard-like form (Saurischia) or a bird-like one (Ornithischia). The meat-eating theropods, such as Tyrannosaurus rex, another meat-eating group called the Herrerasauridae, and the long-necked plant-eating sauropods, such as Diplodocus, all fell within the lizard-hipped Saurischian group. (The dinosaur group that later gave rise to modern birds, the theropods, were, oddly, on the lizard branch of the family tree.) The Ornithischians includes the relatives of Stegosaurus and Triceratops
Dinosaur classification (Zureks)Dinosaur classification (Zureks)

Ornithischian hip bone, left side (Ballista)Ornithischian hip bone, left side (Ballista)The study, which took place at the Natural History Museum in London, involved thousands of bones from 75 different species—many of which have been discovered only in the past 30 years. Research leader Matt Baron of the University of Cambridge found that, apart from the difference in hip bone shapes, there were actually a number of striking similarities between Ornithischians and theropods. These included the shape of the skull, hind limbs and ankle bones. 

Proposed reclassification (© N.Tamura)Proposed reclassification (© N.Tamura)So Baron and his colleagues now propose that theropods should be therefore be switched over to become an offshoot of the same branch of the dinosaur family from which Stegosaurus and Triceratops are descended. They say that the new group of Ornithischia and Theropoda should be given a new name: the Ornithoscelida.

Triceratops with feathers (Nobu Tamura)Triceratops with feathers (Nobu Tamura)
The proposal raises the possibility that feathers first appeared in ancestors common to both the T. rex branch and the Stegosaurus branch of the family tree. A number of theropods are known to have had feathers (including, of course, their descendants, the birds). Maybe Stegosaurus and Triceratops, usually portrayed as bulky, scaly beasts, had feathers too.

DiplodocusDiplodocusIf the dinosaur family tree does become accepted, a new formal definition of dinosaurs will also be needed. In the new tree, two branches, the Ornithischians and theropods, are closer to each other than they are to the Saurischians. This means that all the long-necked, plant-eating sauropods, such as Diplodocus and Brachiosaurus, would now, strictly speaking, be outside the dinosaur family. 

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