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Re: Lagosuchus

>_Lagosuchus_ was close to, but not quite, a dinosaur.  I often see the 
>character "perforated acetabulum" as defining dinosaur, but _Lagosuchus_ 
>had that trait (and, yes--I know there are even other non-dinosaurian 
>reptiles having perforated acetabula).  Then, I've seen three sacral 
>vertebrae specified for dinosaur, but apparently _Herrerasaurus_ and 
>_Eoraptor_ still had only two "fully incorporated" (as labeled by Sereno 
>and Novas) sacral vertebrae.  
>So, I'm not sure what to say it REALLY is that shows _Lagosuchus_ is not 
>a dinosaur.  Can anyone help me with this one?  Thanks in advance.

_Lagosuchus_ (or _Marasuchus_) is not a dinosaur because the most
parsimonious distribution of derived character states yields a position
outside of the node joining birds and _Triceratops_ (or _Megalosaurus_ and
_Iguanodon_).  It is very close to that group, but has not yet been
demonstrated to lie within that clade (and hence is not a dinosaur).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661