WHAT?! A Massive Dinosaur Family Tree Rewrite

A new study about the relationships between species just knocked down our basic understanding of the dinosaur family tree. (Credit: Gary Larson/The Far Side) Ask any obsessive dino-phile above kindergarten age to explain the dinosaur family tree and it's likely the first thing you'll hear is that all dinosaur species fall into one of two groups. It's a core concept upon which our entire understanding of dinosaurs is built. But according to a new study, we got that most fundamental aspect of dinosaur evolution completely wrong. Oops. For more than a century, the dinosaur family tree was understood as having a very early split into two branches: Saurischia and Ornithischia. While science has not yet nailed down exactly when dinosaurs evolved, conventional thinking put the big saurischian-ornithischian split at least 230 million years ago, soon after the Dawn of Dinosaurs itself. The saurischians, or "lizard-hipped," then split into sauropodomorphs (mostly quadrupedal, long-necked, long-tailed herbivores) and theropods (mostly carnivorous, bitey bipeds of all shapes and sizes and degrees of bitey-ness). The ornithischians ("bird-hipped") went on to diversify into some of the whackier herbivore dinosaurs, from horned and frilled ceratopsians to bipedal duck-billed dinos. Despite being "bird-hipped," by the way, the ornithischians have nothing to do with modern birds, which evolved from a theropod lineage. The word Ornithischia comes from the structure of the pelvis. In saurischians, the pubis bone points forward; in ornithischians, it points backward, much like in modern birds, an example of convergent evolution (when unrelated species happen to evolve the same trait). (Sidenote: that's a fun fact to trot out when you want your non-dino-loving friends to reply with comments such as "I can't believe you're still into dinosaurs. At your age," and "This is why you're still single." Then again, if you have non-dino-loving friends, ditch them. You don't need that kind of negativity in your life.) In addition to birdy hips, the ornithischians are also unique for their predentary, a pointy bone at the front of the lower jaw likely used to crop vegetation for noshing.