What is a dinosaur?

["King, Norm" <nking.ucs@smtp.usi.edu>]

Dinogeorge wrote (01/10/96; 9:27p):

>The simplest definition of a dinosaur is cladistic (amazingly enough): a
>dinosaur is any archosaur descended from the common ancestor of the 
genera
>_Megalosaurus_ and _Iguanodon_, which coincidentally are the first two
>dinosaur genera to be scientifically described. This set of animals 
includes
>a wide variety of creatures, even modern birds.


Yes, but show an average person a stegosaur, and she will have no idea 
whether it was descended from the common ancestor of _Megalosaurus_ and 
_Iguanodon_.

I like Colin McHenry's (posting of 01/11/96; 12:10a) suggestion that all 
of these large, extinct reptiles could be called saurians.  But is 
saurian (as in "Sauria") used already to refer to a formal taxonomic 
category?  Assuming we can use that term, then you could specify that 
"true" dinosaurs are saurians that have an erect posture (their legs 
extend vertically beneath the body, as in horses, elephants, and birds).  
Yes, I know there has been some debate about the posture of pterosaurs 
(and let's wait until there is a consensus about it before including 
pterosaurs with the dinosaurs), and if you want to leave no doubt about 
also excluding the swimmers, you could say that dinosaurs are non-flying 
terrestrial saurians with erect posture.  Actually, it may be adequate 
just to say "saurians with erect posture."


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Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu