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Re: Amazing Tendaguru and the most prolific localities in the world

Mike Taylor wrote:

The basic situation is that _no_ significant differences have been demonstrated between the _B. altithorax_ and _B. brancai_ material.

Trouble is, the same could be said for much of the British brachiosaurid material as well. _Pelorosaurus_ could just as easily be referred to _Brachiosaurus_.

> A brachiosaurid skull (USNM 5730) from the Morrison Formation,
> described by Carpenter and Tidwell (1998), has been referred to
> _Brachiosaurus_.

Only tentatively.  In point of fact, I think there is rather more
reason to think that this skull lies outside _Brachiosaurus_ than that
_B. brancai_ does.

At the current time, there is no evidence that more than one brachiosaurid species existed in the Morrison (AFAIK). As you alluded to, the alleged brachiosaurid _Ultrasaurus_ is a synonym of _Supersaurus_, and the same is probably true of _Dystylosaurus_. USNM 5730 certainly belongs to a brachiosaurID, and you are right in saying that there is no positive evidence that it belongs to _Brachiosaurus_. We will need more material to settle the question of whether USNM 5730 belongs to _B. altithorax_. A reasonably complete _B. altithorax_ skeleton would really help. :-)

The only reason to think the skull is _B. altithorax_ at all is because it resembles that of _B. brancai_,

Yes, that's one reason. Another reason is that _B. altithorax_ is the only named brachiosaurid known from the Morrison. Of all the named sauropods from the Morrison, _B. altithorax_ is (so far)the best candidate for the owner of the skull. The only other possibility is that the skull belongs to a second, as-yet-unknown species of Morrison brachiosaurid. (Carpenter and Tidwell certainly do not remove this possibility.)

so if _brancai_ is removed from _B._, then the referral of the skull collapses!

I don't think so, on account of the fact that the skull USNM 5730 looks like it comes from a brachiosaurid (or a close relative, i.e., another basal titanosauriform), based on a comparison to _B. brancai_ and _Atlasaurus_.

I also note that Carpenter and Tidwell are happy to use _B. brancai_ consistently throughout their paper.

True - but the raison d'etre of their study was the description of USNM 5730, not a phylogeny of brachiosaurids.

Isn't this putting the cart before the horse?  If we are going to pay
more than lip-service to phylogenetic classification, we must surely
resist the temptation to name specimens on the basis of where they
were found.

I agree with you here. In general, the final decision should be phylogenetic analysis, and this requires a thorough anatomical study of both the Morrison and Tendaguru brachiosaur material. I agree that specimens should not be named based on geography alone. But historically the genus _Brachiosaurus_ has gone to the opposite extreme. We had _Brachiosaurus_ species from North Africa (_B. nougaredi_) and Europe (_B. atalaiensis_) as well - although the latter was recently removed to its own genus (_Lusotitan_).

Cheers

Tim