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Reclassifying Dinosaurs

Wikimedia Commons | Allie_Caulfield / Wikimedia Commons New proposal rearranges several dinosaurs on the family tree, including the tyrannosaurus (top) and the triceratopsWikimedia Commons | Allie_Caulfield / Wikimedia Commons

A computer model created by paleontologist Matthew Baron, a PhD student at Cambridge University, compared the data on 457 anatomical traits of 74 species of dinosaurs in just five minutes. Controversially, the analysis refuted much of the knowledge accumulated over the last 130 years about these reptiles that lived 240-66 million years ago (Nature, March 23). According to the study, which suggests new familial relationships between species and rearranges the evolutionary tree, dinosaurs should not be divided into two large groups, as has traditionally been the case. Paleontology books separate them into Ornithischia, which have a pelvic structure similar to birds, and Saurischia, whose anatomical structure resembles that of lizards. The former includes herbivorous dinosaurs only, many with plates on their backs, such as the triceratops and stegosaurus. The latter comprises the theropods (biped and carnivorous dinosaurs), such as the famous tyrannosaurus, as well as a group of large, long-necked herbivores called sauropodomorphs. Paradoxically, the birds of today are descended from the Saurischia group, and not from the Ornithischia. Baron has defended the new classification, which suggests that the theropods are placed with the Ornithischia in a group called Ornithoscelida, and that the sauropodomorphs are grouped with the herrerasaurids, one of the first known types of dinosaur, in a redefinition of the Saurischia category. Another controversial element of the study concerns the supposed place of origin of the dinosaurs. Fossil material currently indicates that South America was the birthplace of these reptiles, but Baron’s work proposes that they may have emerged in the Northern Hemisphere, perhaps in what today is Scotland.