One Of The Most Basic Facts About Dinosaur Family Trees Might Be WrongThis week the dinosaur world is buzzing because of a new paper that suggests the way we classify dinosaurs may be very wrong. Back in 1888, Harry Seeley, a paleontologist said that all dinosaurs fall into two categories: lizard-hipped (Saurischia) and bird-hipped (Ornithischia). This has been accepted ever since. But a study published this week in Nature suggests that this division is wrong, essentially challenging the most basic section of dinosaur genealogy.

Under Seely’s original organization, the bird-hipped dinosaurs include ones with armor and horns, like the Stegosaurus and Triceratops. The lizard-hipped ones include sauropodomorphs like Brontosaurus and theropods like the T-rex. Matthew Baron, a doctoral candidate at the University of Cambridge, studied dinosaur fossils from around the world and cataloged them depending on 457 different features. Then, he used a computer program to study them. Based on these features, the computer program recommended the arrangement that makes the most sense and it wasn’t the one that already existed.

The new tree puts the theropods which were primitively considered lizard-hipped together with the bird-hipped dinosaurs into a combined group. As Ed Yong of The Atlantic put it, “This is like someone telling you that neither dogs nor cats are what you thought they were, and some of the animals you call ‘cats’ are in reality dogs.” This proposal is not written in stone, and it might not be fully accepted. Kevin Padian, a biologist at the University of California, Berkeley said, “It’s a profound proposal with a reasonable basis but no one expects it will be the last word.”

He continued that dinosaur classification can be tricky because there have been so many new discoveries in the past few decades and a lot of these dinosaurs have evolved in ways that make it hard for them to place on the family tree. So don’t be too fast to think that just because this key division is wrong, dinosaur experts don’t know what they are talking about. But it may time to look a little more closely.