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Hank fixes those of us who are probably wrong about what is and is not a dinosaur... and gives a refresher to those of us who do know this already.

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[intro music] Hank Green: You are probably wrong about what is and is not a dinosaur, but fear not -- I am going to fix you. For instance, pterodactyls? Not dinosaurs. Hummingbirds? Dinosaurs. Also, Pluto? Still not a planet. The official definition of a dinosaur is land-dwelling diapsid reptile descended from archosaurs. Diapsids are reptiles that have or used to have two specialized openings in their skulls that allow for a bigger, stronger bite, and archosaurs are a kind of diapsid that were defined by a whole bunch of shared characteristics, including two additional holes in the skull right behind the eyes. Point is, the pterodactyl was both of those things, but pterodactyls hung out mostly in the air, not on the ground, and so they weren't land-dwelling. Plus, when they were on the ground, pterodactyls walked with a kind of semi-upright stance that differed from the straighter stances of real dinosaurs. Paleontologists, turns out, are a bit picky. Another problem with pterodactyls being dinosaurs is that pterodactyls really even a thing. The term "pterodactyl", Greek for "wing-finger", was coined by French naturalist and zoologist Georges Cuvier, around the turn of the 19th century. People had started digging up all sorts of weird beaky/wingy fossils, and Cuvier was like, "Oh, those! They're, uh, they're pterodactyls. Please place them in the pterodactyl bucket in the corner." But eventually paleontologists renamed the entire group of flying reptiles "pterosaurs", or "winged lizards", and their many diverse species all got their own scientific names. As far as modern paleontologists can tell, during the Jurassic and Cretaceous periods these carnivorous lizards ruled the skies, and some of them were frickin' huge. The Quetzalcoatlus, the biggest scientists have ever found evidence of, had a 12 meter wingspan. It's probably the biggest thing that ever flew. Ever. So obviously pterosaurs share a lot of characteristics with birds: the ability to fly, big brains relative to their body size, lightweight bones... but birds did not evolve from pterosaurs. Pterosaurs were wiped out by whatever it was that offed most of the dinos. Instead, birds evolved from little two-legged land-based dinosaurs that survived the giant cataclysmic supercrap that befell the Earth 65 million years ago. The fact that pterosaurs and birds have similar adaptations for flight is a nice example of what we call convergent evolution, two unrelated animals evolving similar features to tackle a specific problem -- in this case, flight. Now, I know what you're thinking. I just said that the official definition of a dinosaur includes being both land-dwelling and a reptile, so how the frick could a bird be considered a dinosaur? Well, the rules of taxonomy are such that direct descendents of a single common ancestor must be included in the same group, so birds are considered a sub-group of dinosaurs, which means that dinosaurs are in fact not extinct. It also means that I can eat one right now. [chomps chicken thigh] I'm eating a dinosaur! Thank you for watching this episode of SciShow. If you got smarter and wanna keep getting smarter, then you should go to and subscribe for more. If you have any questions or suggestions or ideas for us, please leave them in the comments below, or on Facebook or Twitter, and we will see you next time. [outro music]