Re: What is a dinosaur?

[Dinogeorge@aol.com]

In a message dated 96-01-12 12:08:38 EST, nking.ucs@smtp.usi.edu (King, Norm)
writes:

>If you tell people that a mosasaur isn't a dinosaur, they will respond by 
>wanting to know why not.  They are sincerely interested.  But you will 
>lose them by saying that it's not a dinosaur because it isn't descended 
>from the common ancestor of _Megalosaurus_ and _Iguanodon_.  People want 
>information they can do something with, rather than impractical 
>theoretical stuff:
>
>    Mosasaurs aren't dinosaurs because they don't have an erect posture.
>    Furthermore, they're not dinosaurs because they were specialized for
>    swimming.  In fact, they were big, aquatic lizards!  
>
>Now that's a story people can follow.  It makes perfect sense, even to 
>someone who has never studied any kind of science.

We're fortunate (so far) that we haven't discovered any dinosaurs that were
aquatically adapted, or that reversed the erect posture of their ancestors in
adapting to a particular lifestyle (which is what the later crocodylians
did). Even though "people can follow" (??) this story, it is misleading to
suggest that mosasaurs "aren't dinosaurs" _because_ "they don't have an erect
posture" and _because_ "they were specialized for swimming." What do you tell
the kid who replies that mosasaurs were simply dinosaurs that could swim and
lived in the water--just like pterosaurs were dinosaurs that could fly?

It would be better to say that mosasaurs aren't dinosaurs simply because they
are not on the same branch of the reptile (or amniote) family tree.