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Re: Apatosaurus vs Brontosaurus
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_).
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