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Toby White wrote:
>At 110My, wouldn't this be the wrong age (early Albian) for a Titanosaur in N.
>America? Yet its too recent to be a Brachiosaur. Very odd.
While we should treat claims of occurrances of a taxon before its
First Appearance Datum (FAD) or after its Last Appearance Datum (LAD), we
should not be at all surprised to encounter it between its FAD and LAD.
Paleozoogeography is an important subject. We must remember, however, that
it is dependant on a special kind of negative evidence: a lack of recovery.
In marine biostratigraphy, with their dandy sedimentary and fossil records,
this is a bit easier to deal with. However, in terrestrial systems, we must
account for not only a much poorer record, but a record with stronger biases
against preservations of certain organisms and environments. For example, in
times of regional sea-level highstand, inland facies are less commonly
preserved. Thus, inland faunas may appear to be lacking in the region. Or,
for that matter, some faunal elements (pterosaurs) are highly dependant on
laggerstadten [sic?] for their preservation, and a lack of such deposits
results in an apparent absence of those groups. So, we should explore some
of these (geological) questions more fully, rather than assuming that a
"well established" absence is necessarily an absence at all.
Dr. 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.
Indeed, there is some questionable evidence of Campanian sauropods.
I encourage anyone interested in this subject to read Spencer Lucas' 1980
(or is it '82?) article in Advances in San Juan Basin Paleontology.
>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.
There may yet be a greater question: whether "brachiosaurids" are an
outgroup to the titanosaurs at all. But that is for another day...
Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
"Why do I sense we've picked up another pathetic lifeform?" - Obi-Wan Kenobi