Rearranging the Dino Family Tree

After 130 years of study, you might think that most of the key facts about dinosaurs, including their family tree, would have been sorted out by now. That’s certainly what paleontologists have thought since 1887, when British paleontologist Harry Seeley divided dinosaurs into two groups based on hip structure: the lizard-hipped saurischians included Tyrannosaurus and Brontosaurus while Triceratops and Stegosaurus were categorized as bird-hipped ornithischians.

Seeley’s dinosaur family tree has been widely accepted ever since — but now another British paleontologist suggests that Seeley got it wrong.

Matthew Baron, a graduate student at the University of Cambridge who works in London’s Natural History Museum, studied 74 species of dinosaurs and species closely related to dinosaurs and compared 457 different physical characteristics. He found that a subgroup of dinosaurs called theropods, formerly classified as saurischians, are, in fact, more closely related to the ornithischians.

New Identities

Baron’s revised dinosaur family tree combines subgroups Therapoda and Ornithischia into a new clade, or parent group, called Ornithoscelida, while the Saurischia clade includes the subgroups Sauropodomorpha and Herrerasaurida. In basic terms, as Ed Yong explains in an article for The Atlantic, “this is like someone telling you that neither cats nor dogs are what you thought they were, and some of the animals you call ‘cats’ are actually dogs.” While most of what researchers currently understand about dinosaurs is unaffected by this new information, the changes to basic facts about the dinosaur family tree will deeply affect the field of paleontology.

Most obviously, Baron’s tree fundamentally changes how paleontologists thought different species of dinosaurs were related. For example, scientists always believed that Tyrannosaurus was more closely related to Brontosaurus than Triceratops, but it now appears that the opposite is true. The tree also suggests that dinosaurs first came on the scene between four and 16 million years earlier than previously estimated, and that they originated in the northern half of the world instead of the southern half.

Baron’s research is an exciting change for paleontologists, and modifications to taxonomy are not as uncommon as they might seem. As recently as 2014, 28 scientific papers were published that changed the way we look at major groups of birds that are alive today. And in its day, Seeley’s classification replaced the 1869 dinosaur subgrouping proposed by Thomas Henry Huxley. While more research is required to confirm Baron’s findings, he’s confident in his results. “We tested and tested and then some,” he said, “and it’s a robust result.”