An article published in the journal “Nature” describes a new hypothesis regarding the relationships within the group of dinosaurs. A team of scientists from the British Cambridge University and the Natural History Museum in London proposed a new structure for the tree of the dinosaur group that heavily restructures the classical groups by assigning a number of new names as well. The scientists also proposed the hypothesis that dinosaurs originated in the northern hemisphere and not in the southern.

The current classification of dinosaurs dates back to the end of 1800 and was decided by accepting the proposal by Harry Seeley to divide them in the orders of saurischians (Saurischia) and ornithischians (Ornithischia). This division was based on the hip structure: the saurischians had bones similar to those of reptile hips while ornithischians had bones similar to those of bird hips. Further research led to the division of saurischians in the suborders sauropodomorphs (Sauropodomorpha), known especially for some huge sauropods (Sauropoda) and theropods (Theropoda).

This classification has been accepted for more than a century but today Matthew Baron, David Norman and Paul M. Barrett proposed an alternative one based on the exam of 457 anatomical characters of 74 species of dinosaurs. According to them, ornithischians and theropods are part of the same group they called Ornithoscelida. Sauropodomorphs were grouped with Herrerasaurs (Herrerasauridae), a family of primitive dinosaurs.

One effect of this new classification is that sauropodomorphs, which include species such as Diplodocus, and other animals such triceratops don’t even fit into the general definition of dinosaurs. It’s a paradox considering that there are some of the most iconic species associated with dinosaurs. The researchers proposed a broader definition for the dinosaur group.

This new classification led the authors to some new conclusions including some on the origin of dinosaurs and their diversification. According to the British paleontologists the most primitive dinosaurs were small and lived in the northern hemisphere. They also proposed the hypothesis that ornithischians didn’t evolve in the Triassic but descended from theropods.

The oldest fossils of these animals were found in South America, suggesting that they originated in that area, in what was then Gondwana. However, the classification review raises doubts about that interpretation, pointing to a possible dinosaur origin in what was then Laurasia. It should be remembered that at the time the continents were much closer so it’s more difficult to understand what is the dinosaurs’ origin area area and where they migrated later.

As for feathered dinosaurs, in the new classification they’re all Ornithoscelida while now some of them are classified as theropods and others as ornithischians. In substance, according to the British paleontologists feathers evolved only once within a group and not independently within the two classic groups.

The discussions on this proposal began immediately after the article in “Nature” was published and who knows how long will go on. According to the authors of the new classification it solves several inconsistencies but it won’t be easy to convince paleontologists to give up a classification used for over a century.