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Jaime Headden wrote:
Not to trod on Jon Wagner's feet, who I believ reported earlier this
year on the DMNH skull, but the specimen (cat. number?) is certainly very
similar to the *B. brancai* (*Giraffatitan*) skulls from Tendaguru, though
there are some noticeable differences in the snout and cranial roof that I
could notice that may indicate specific separation.
The paper is:
Kenneth Carpenter and Virginia Tidwell. (1998). Preliminary description of a
_Brachiosaurus_ skull from Felch Quarry 1, Garden Park, Colorado. In: The
Upper Jurassic Morrison Formation: An Interdisciplinary Study. Kenneth
Carpenter, Danial Chure and James Kirkland eds. Modern Geology Vol. 23 No
1-4. pp. 69-84.
Worth checking out. The "_Brachiosaurus_ sp." skull (USNM 5730) is the
largest sauropod skull so far to be found in the Morrison Formation. As
Jaime says, it does show substantial differences to the skull of the
Tendaguru species, _B. brancai_. In many ways, the _Brachiosaurus_ sp.
skull is intermediate between _Camarasaurus_ and _B. brancai_, especially
the snout (shorter maxilla with more teeth), skull roof, and perhap the
dentition (the only known tooth is more like _Camarasaurus_).
If USNM 5730 does turn out to be the skull of _B. altithorax_, it would add
further support to the generic separation of _B. altithorax_ and _B.
brancai_ (the latter becoming the type species for _Giraffatitan_).
As Salgado, Calvo and other workers have pointed out, there are no unique
derived features shared by _B. altithorax_ and _B. brancai_. Most of the
so-called autapomorphies of the genus _Brachiosaurus_ (and the family
Brachiosauridae sensu McIntosh) are in fact primitive for the
Titanosauriformes. The one derived feature that might have been used to
unite the two species (humerus at least as long as the femur) is also found
in _Atlasaurus_ (and perhaps at least one European brachiosaur).
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