Re: Apatosaurus vs Brontosaurus

[Tim Williams <twilliams_alpha@hotmail.com>]

Ken Carpenter wrote:

> "The limbs of A. louisae are noticeably more robust than in the other two 
> species [A. ajax and A. excelsus]. Gilmore (1936), p. 268) has also cited a 
> number of other characters which separated A. louisae from A. excelsus. As 
> Riggs (1903) has already pointed out, the separation of A. louisae from A. 
> ajax is more difficult. Based on four speci[mens] of the Tithonian A. ajax 
> and a half dozen skeletons of the older Kimmeridgian A. excelsus, it is 
> clear that the adult A. ajax is some 10% larger than its geologically older 
> relative. Size along can hardly justify the separation of species (McIntosh 
> 1990)... For the present it would appear to be prudent to retain A. ajax 
> and A. excelsus." McIntosh, J.S. 1995. Remarks on the North American 
> sauropod Apatosaurus Marsh. Sixth Symposium on Mesozoic Terrestrial 
> Ecosystems and Biota, Short Papers. 119-123.

I wasn't aware of this article - thanks.  I'll try and get a hold of it.

I can understand why it could be tricky to separate _A. ajax_ from _A. 
excelsus_ - after all, how does one distinguish a large _excelsus_ from an 
average-sized _ajax_?  I know _excelsus_ is stratigraphically older than 
_ajax_ (which is roughly contemporary with _Amphicoelias_), and I wonder if 
there is a gradual increase in the size of _Apatosaurus_ as one goes up the 
Morrison?  Alternatively, if some exceptionally large _Apatosaurus_ elements 
were found in the Kimmeridgian, it would make the _ajax_/_excelsus_ 
distinction very shaky (assuming that they don't belong to _louisae_).


Cheers

Tim

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