[ksherlock]

I'm not a dinosaur expert (but this is hacker news, so...). You know who else wasn't a dinosaur expert? All those people back in the 1800s who lumped theropods, sauropods, and everything else together and called them dinosaurs. So now the definition of dinosaur is, paraphrased from wikipedia, "anything from descended from the most recent ancestor of all the stuff we want to call a dinosaur". I can believe ostriches and elephant birds and small theropods are related. Can you believe the possibly imaginary Brontosaurus and T Rex are related? Is there an intellectually honest reason to lump them together?

[quadrangle]

Sure, there's an intellectually sound reason for the lumping: There was a long period of earth's history where enormous reptiles were prominent, and almost all but the crocodile family died out. So, it makes sense to have a word for all the age-of-reptiles reptiles we see in fossils. "Dinosaurs" works great. As such, it includes pterosaurs and sea reptiles even.

[ksherlock]

plesiosaurs and pterosaurs aren't currently considered dinosaurs.

[avip]

Brontosaurus was rebranded as Apatosaurus.

[stan_rogers]

Sort of. Apatosaurus was first, so Brontosaurus lost out as a junior synonym (first to name the things get to name the things, which gives us a silly name meaning "hyrax-like beast" - hyracotherium - for something that's obviously the dawn horse - eohippus)... except that there's very good reason now to believe that they weren't the same species.