Re: Where to draw the line.

[David Marjanovic <david.marjanovic@gmx.at>]

>      Dr. McIntosh pointed out to me that the presence 
> of a forward expansion on the cervical ribs in _A. 
> excelsus_ and the lack of the expansion in _A. 
> louisae_ is a main characteristic that separates the 
> two species. Since then I have become convinced that 
> this can no longer be used as a trait to separate the 
> two species. 
 
Congratulations!!! You've hit the nail on the head. 
 
Mathew J. Wedel & R. Kent Sanders: Osteological correlates of cervical 
musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments 
on the cervical ribs of *Apatosaurus*, PaleoBios 22(3), 1 -- 6 (15 
December 2002) 
 
A few random quotes... 
 
"The absence of anterior processes of the cervical ribs has traditionally 
been regarded as an autapomorphy of *Apatosaurus louisae*. However, 
anterior processes are weakly developed or absent in some specimens of *A. 
ajax* and *A. excelsus*, so this character is probably less diagnostic 
than previously assumed." 
"[...] we consider the taxonomic utility of anterior processes to be 
suspect." 
"the presence or absence of anterior processes is probably not useful for 
discriminating species of *Apatosaurus*." 
 
> What are the characteristics that paleontologists look 
> for to determine whether _Apatosaurus) material is 
> that of _A. excelsus_, _A. ajax_ or _A. louisae_? 
> (cervical differences or otherwise). 
> 
>                                        -Michael Lima 
 
Maybe there are none anymore. :-) 
 
BTW, if there's a university near you, I'm sure the library is public. The 
university libraries over here are public, just that the general public 
doesn't know that. :-) 

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