More than a century of theory about the evolutionary history of dinosaurs has been turned on its head following the publication of new research from scientists at the University of Cambridge and Natural History Museum in London. Their work suggests that the family groupings need to be rearranged, re-defined and re-named and also that dinosaurs may have originated in the northern hemisphere rather than the southern, as current thinking goes.
For 130 years palaeontologists have been working with a classification system in which dinosaur species have been placed in to two distinct categories: Ornithischia and Saurischia. But now, after careful analysis of dozens of fossil skeletons and tens of thousands of anatomical characters, the researchers have concluded that these long-accepted familial groupings may, in fact, be wrong and that the traditional names need to be completely altered.
This new analysis of dinosaurs and their near relatives, published today in the journal Nature, concludes that the ornithischians need to be grouped with the theropods, to the exclusion of the sauropodomorphs. It has long been known that birds (with their obviously ‘bird-like’ hips) evolved from theropod dinosaurs (with their lizard-like hips). However, the re-grouping of dinosaurs proposed in this study shows that both ornithischians AND theropods had the potential to evolve a bird-like hip arrangement- they just did so at different times in their history.
That resolves a long-standing question: Why would birds have descended from the non-bird-like type of dinosaur. It turns out they didn’t, or not exactly.
“The carnivorous theropods were more closely related to the herbivorous ornithischians and, what’s more, some animals, such as Diplodocus, would fall outside the traditional grouping that we called dinosaurs. This meant we would have to change the definition of the ‘dinosaur’ to make sure that, in the future, Diplodocus and its near relatives could still be classed as dinosaurs.” Paper. (paywall) – Matthew G. Baron, David B. Norman, Paul M. Barrett. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature, 2017; 543 (7646): 501 DOI: 10.1038/nature21700More.
Hmmm. That last point raises an interesting question: Maybe they weren’t really dinosaurs. Keep the file open.
The new approach, as noted above, also suggests that dinosaurs may have originated in Laurasia, not Gondwana:
For many years, it was thought that dinosaurs originated in the southern hemisphere on the ancient continent known as Gondwana. The oldest dinosaur fossils have been recovered from South America suggesting the earliest dinosaurs originated there. But as a result of a re-examination of key taxa it’s now thought 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.
Mourning a lost dino world with Ed Yong at the Atlantic:
For most of my life, I’ve believed that the dinosaurs fell into two major groups: the lizard-hipped saurischians, which included the meat-eating theropods like Tyrannosaurus and long-necked sauropodomorphs like Brontosaurus; and the bird-hipped ornithischians, which included horned species like Triceratops and armored ones like Stegosaurus. That’s how dinosaurs have been divided since 1887. It’s what I learned as a kid. It’s what all the textbooks and museums have always said. And according to Baron, a Ph.D. student at the University of Cambridge, it’s wrong.
Partly, people may have been blinded by their preconceptions. The split between saurischians and ornithischians was first proposed in 1887 by British paleontologist Harry Seeley, who divided the groups based on the shape of their hips—a seductively obvious difference. “When you look at specimens, it’s very quick and easy to say: that’s a saurischian, that’s an ornithischian, and never the two shall meet,” says Baron. “People then go into their studies with that mindset, and Seeley’s idea has never been rigorously tested.” More.
That’s twice we’ve lost them now: Their extinction and the loss of an easily grasped cultural myth 😉
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