A new Nature study threatens to turn more than a century’s worth of paleontology on its head. As it turns out, we may have been thinking about dinosaurs wrong all this time – and it’s all thanks to an overly strong focus on nothing less than their pelvises.
Once upon a time, for around 180 million years, non-avian dinosaurs ruled the world. Scientists decided to split them between two primary groups, the Ornithischia and the Saurischia.
The former included the docile Iguanodon, the armored Triceratops, and the spiked Stegosaurus, whereas the latter featured the gigantic herbivorous titanosaurs, the classic Tyrannosaurus rex, and the mortifying Megaraptors. The Saurischia also included the theropod subset of dinosaurs, whose feathered descendants eventually gave rise to birds.
What on Earth, you may be wondering, originally segregated dinosaurs into these two incredibly diverse groups? Well, it was the structure of their hip/pelvis, which came in two distinct variants – and for 130 years, this has defined the two major dinosaurian groups for scientists.
This new study, composed by researchers at the University of Cambridge and London’s Natural History Museum, took a look at an incredibly wide range of early dinosaurs in order to reassess the wisdom of basing so much off the two different types of hip/pelvis.
Spinosaurus, a particularly awesome theropod dinosaur. Herschel Hoffmeyer/Shutterstock
They discovered that at least 21 other physical features, including sharp attachments to jawbones and very distinct bones in their feet and claws, meant that the theropod group – which contained Velociraptors, Tyrannosaurs and birds – is actually a sister group to the Ornithischia, not the Saurischia.
In retrospect, this change is long overdue. Based on their appearance, the Saurischian hip joint is described as “lizard-like,” and the Ornithischian type is described as “bird-like.”
It’s been long-established that birds evolved from the theropods, but the fact that this placed them in the “lizard-hipped” Saurischia dinosaur group was always incredibly confusing. This new study places the theropods within the same group as the “bird-hipped” dinosaurs. Finally, it all makes sense.
“It is odd that this hypothesis has survived relatively unmolested for so long given, as you say, the radical changes that have occurred in our understanding of all other groups on Earth,” lead author Matthew Baron, a graduate student of palaentology at the University of Cambridge, told IFLScience.
“I guess because it is a simple and elegant idea,” he added. “Finally, we have shown that the old definition for dinosaur needed an update.”
The new assessment of dinosaurian evolution moves a few other subgroups around too, including placing a primitive type of meat-eating beastie within the same group as the long-necked plant-eating dinosaurs such as the Brontosaurus and Diplodocus.
“One thing that this has thrown up is the new way we have to think about the ancestral dinosaur and how it lived,” Baron noted.
The earliest dinosaurs, which emerged out of the Great Dying mass extinction event around 250 million years ago, are decidedly mysterious beings, with fossil evidence dating back to the Early Triassic being of fairly poor quality. Researchers, however, can use later dinosaur fossils to infer what their distant ancestors might have looked like.
This study is no different, and based on its newly arranged family tree, the first dinosaurs were probably small, omnivorous, walked on two legs, and had grasping hands. Scientists previously thought the first dinosaurs evolved in the Southern Hemisphere, but this study implies they first emerged in the north.
The American Museum of Natural History's Tyrannosaurus specimen. J M Luijt/Wikimedia Commons; CC BY-SA 2.5 nl
In sum, the entire evolutionary tree of the dinosaurs has been thrown into disarray.
This research currently stands alone in terms of its bold, new ideas. If, however, it’s eventually backed up by other paleontology groups, it could be, in time, considered something truly revolutionary.