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RE: Sauroposeidon




Tom Holtz wrote:

It is most assuredly not too recent for a brachiosaur, as at least SOME of
the _Astrodon_/_Pleurocoelus_ material (contemporaneous with
"Sauroposeidon") seems to be brachiosaurid.  Furthermore, there is now
evidence of titanosaurs in North America by the mid-Cretaceous.

According to Salgado, the "Pleurocoelus" material from the Early Cretaceous of Texas is bona fide titanosaurid, judging from the procoelous anterior tail vertebrae. The _Astrodon_/_Pleurocoelus_
type material from Dr Holtz's stomping ground of Maryland, on the other hand, is probably basal titanosaur. Its tail vertebrae are different to the Texas sauropod.



Of course, there is the whole question now of what other than _Brachiosaurus
altithorax_ and _B. (sometimes _Giraffatitan_) brancai_ IS a brachiosaurid.
It may be that "Brachiosauridae" in the old more inclusive sense includes a
paraphyletic grade of titanosaur outgroups.

As somebody pointed out recently (and for the life of me, I can't remember who), there's no apomorphic characters that link the Tanzanian/Tendaguru _Brachiosaurus_ (_B. brancai_) with the type species (_B. altithorax_) from the Morrison. All the characters that link the two species, and have been used to diagnose the genus _Brachiosaurus_, are primitive titanosaur traits. (This also applies to the family Brachiosauridae in the old more inclusive sense.)


The humerus/femur ratio shared by the two _Brachiosaurus_ species has also been questioned. This was news to me when I read it, but the humerus of _B. brancai_ is apparently incomplete. The two species may not be comparable in this respect.

Remember, _Brachiosaurus altithorax_ is one of the more poorly known sauropods from the Morrison. I agree with George in separating the Tendaguru species into a separate genus, _Giraffatitan_.


Tim

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