Re: Apatosaurus vs Brontosaurus

[Ken Carpenter <KCarpenter@dmns.org>]

"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.


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 >>>

Matt Wedel (via Mike Taylor) wrote:

>Whoa, hoss.  Kent and I shot down _one_ character that supports A.
>louisae as distinct from A. excelsus.  That still leaves 15 or so by
>Gilmore's count.

But how many of Gilmore's 15 or so characters are still considered valid?  
McIntosh (1990), in his chapter on Morrison sauropod taxonomy in the 
_Dinosaur Systematics_ volume, was less than enthusiastic about most of the 
characters used by Gilmore (1936) to distinguish _A. louisae_ from _A. 
excelsus_.  For example, McIntosh regarded the three characters based on the 
shape of the scapula as subject to intraspecific variation, and he dismissed 
all of Gilmore's hypopsphene characters.

Nevertheless, McIntosh (1990) did regard _A. louisae_ as distinct from _A. 
excelsus_, and put forward three characters to distinguish the two species: 
(1) Anterior extension of the cervical ribs (present in _excelsus_, absent 
from _louisae_); (2) an accessory lamina subdividing the 
infrapostzygapophysial cavity (try saying that three times!) of the mid- and 
posterior cervicals (present in _excelsus_, absent from _louisae_); (3) very 
robust hindlimb bones in _louisae_ (especially the femur).

As discussed previously, (1) has since been refuted as a useful diagnostic 
character, since the shape of the cervical ribs varies within a species.  
That leaves only two characters to distinguish _A. louisae_ from _A. 
excelsus_: the accessory lamina character and the relative robustness of the 
leg bones.   Maybe there are other characters that can be used to diagnose 
_A. louisae_, and maybe some of the characters proposed by Gilmore are 
useful after all.  However, based on the published literature, Gilmore's 15+ 
characters have been whittled down to only two, neither of which have been 
re-examined recently AFAIK.



Tim

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