New study redraws family tree of dinosaur

Dinosaurs may have originated in the northern hemisphere rather than the southern, according to a new study that overturns more than 130 years of research and radically redraws the family tree of the prehistoric reptiles.

The finding also suggests that family groupings of dinosaurs need to be rearranged and re-named.

For more than a century, palaeontologists have been working with a classification system in which dinosaur species have been placed in to two distinct categories - Ornithischia and Saurischia.

However, after careful analysis of dozens of fossil skeletons and tens of thousands of anatomical characters, researchers at the University of Cambridge and Natural History Museum in London have concluded that the long-accepted familial groupings may, in fact, be wrong and that the traditional names need to be completely altered.

It was earlier thought that dinosaurs originated in the southern hemisphere on the ancient continent Gondwana. The oldest dinosaur fossils have been recovered from South America suggesting the earliest dinosaurs originated there.

However, the re-examination of key taxa shows that they could just as easily have originated on the northern landmass known as Laurasia, though it must be remembered that the continents were much closer together at this time.

"This study radically redraws the dinosaur family tree, providing a new framework for unravelling the evolution of their key features, biology and distribution through time," said Paul Barrett of the Natural History Museum in London

"If we're correct, it explains away many prior inconsistencies in our knowledge of dinosaur anatomy and relationships and it also highlights several new questions relating to the pace and geographical setting of dinosaur origins," said Barrett.

Dinosaurs were first recognised in 1842. Over subsequent decades, various species were named as more and more fossils were found and identified.

During the latter half of the 19th century it was realised that dinosaurs fell quite neatly into two distinct groupings, or clades; Saurischia or Ornithischia.

This was based on the arrangement of the creatures' hip bones and in particular whether they displayed a lizard-like pattern (Saurischia) or a bird-like one (Ornithischia).

As more dinosaurs were described it became clear that they belonged to three distinct lineages; Ornithischia, Sauropodomorpha and Theropoda.

In 1887 Seeley placed the sauropodomorphs (which included the huge 'classic' dinosaurs such as Diplodocus and Brontosaurus) together with the theropods (which included T rex), in the Saurischia.

The ornithischians and saurischians were at first thought to be unrelated, each having a different set of ancestors, but later study showed that they evolved from a single ancestor.

This new analysis of dinosaurs and their near relatives concludes that the ornithischians need to be grouped with the theropods, to the exclusion of the sauropodomorphs.

The study was published in the journal Nature.