To get technical about it, since the family Hadrosauridae is anchored on Hadrosaurus, hadrosaurus can’t not be a hadrosaur. It’s all the other “hadrosaurs” that wouldn’t be hadrosaurs if Hadrosaurus isn’t a hadrosaur (but could a hadrosaur chuck wood…?).
The same situation exists with other names for well-known dinosaur groups (titanosaurs, megalosaurs). In those cases there’s been a push to abandon the family names based on dubious species. This hasn’t happened with hadrosaurs (and ceratopsians for that matter, as Ceratops itself is very fragmentary) largely becuase the names are so well known and widely used.
True. Were Hadrosaurus found to not be a “hadrosaur”, the group name would probably become something like Edmontosauridae (Trachodontidae technically has familial priority, but since Trachodon is itself considered an invalid genus, the next in line appears to be Edmontosaurus for being designated the “type genus” for the family). Given that the postcrania of Hadrosaurus match the rest of the hadrosaurines pretty well (the skull having never been found, for those who weren’t aware), though, it’s unlikely that such a thing will occur. Nevertheless, Hadrosaurus remains a nomen dubium, at least until a skull is found.
As for ceratopsians, as of 1995, at least, it appears that Ceratops is valid. Titanosaurus and Megalosaurus, and their associated familial names, etc., however, are still in trouble.
Also, as a minor correction to my post above, there was one species of Anatosaurus which was not renamed to Edmontosaurus: Anatosaurus copei was renamed as Anatotitan copei…though there is, of course, debate as to whether Anatotitan is really distinct from Edmontosaurus.
