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Grefory Paul wrote:
Because there are significant differences between what is known of B.
altithorax and brancai I applied a new subgeneric title to the latter in
additional fossils of the former verify the designation, or require a
separation. Wanted to do it myself since the African species deserved a
appropriate name. Although the Morrison brachiosaur skull tends to favor
separation, the situation has not changed enough yet for full distinction
proposed. If and when additional Morrison remains require a generic
it has to be Giraffatitan.
The skull in question (USNM 5730), designated "_Brachiosaurus_" sp. is
certainly different from that of _B. brancai_; but whether it warrants
generic separation from the Tendaguru brachiosaur (_brancai_) is a
subjective decision. Further, we cannot be 100% sure that USNM 5730 belongs
to _Brachiosaurus altithorax_ since, although the skull certainly comes from
a brachiosaurid (or at least a basal titanosauriform), it was not associated
with _B. altithorax_ skeletal elements AFAIK, and there may be more than one
brachiosaur in the Morrison. Carpenter and Tidwell (1998) deliberately held
off referring USNM 5730 to _altithorax_.
Less important than how different _brancai_ and _alithorax_ are is where
they fall out in phylogenetic analysis. If the characters shared by
_brancai_ and _altithorax_ are all basal titanosauriform characters, and the
two species share no unique derived characters, then this is a strong case
for splitting the species into separate genera. Relationships within the
basal titanosauriform nexus are a little tangled and confused, and many
characters used to diagnose the Brachiosauridae have been shown to be basal
The "tall shoulders" of brachiosaurids (forelimbs much longer than the
hindlimbs) have been regarded as the hallmark of this group, and this
character alone should be enough to bring together _brancai_ and
_altithorax_ (and perhaps some European taxa) to the exclusion of other
titanosauriforms. However, it has been suggested that the striking
forelimb/hindlimb disparity of brachiosaurs has been exaggerated, and
inspired by the Humbolt mount of _B. brancai_ that was composed of elements
from different-sized individuals:
And, yes, _Giraffatitan_ is a cool name, IMHO.
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