Re: Apatosaurus vs Brontosaurus

[Ken Carpenter <KCarpenter@dmns.org>]

It is alleged that many dinosaurs increase in size stratigraphically in the 
Morrison, but the evidence is shaky, especially if you don't consider large 
specimens lower in the Morrison.

Kenneth Carpenter, Ph.D.
Curator of Lower Vertebrate Paleontology &
Chief Preparator
Dept. of Earth Sciences
Denver Museum of Natural History 
2001 Colorado Blvd.
Denver, CO 80205

Phone: (303)370-6392
Fax: (303)331-6492
email: KCarpenter@DMNS.org

For fun:
 http://dino.lm.com/artists/display.php?name=Kcarpenter


>>> Tim Williams <twilliams_alpha@hotmail.com> 27/May/04 >>>
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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