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Re: Oviraptor



Tim Donovon (sirius531@yahoo.com) wrote:

<Saurolophus is known only from the early Maastrichtian units 3 and 4 of the
Horseshoe Canyon, and does not occur in the Campanian units 1 and 2. The Nemegt
dinosaur fauna has virtually nothing in common with the Judithian. Shuvalov
wrote that Nemegtian ostracods, gastropods etc indicate a Maastrichtian age.>

 The Nemegtian and Judithian have been correlated on non-ostracod and gastopod
data, as explained in some other, extensive, posts. Check the archives for
earlier discussions. I was using this not to argue for "right vs wrong" but to
say that other data say other things, and that the comparative use of
differentiating them is subjective. The totality of the data does not support
comparable results, so something is amiss.

<Santonian-Campanian boundary. Turnover among large taxa was often faster.>

  Based on? This boundary is also relative, as the major localities of the
Djodokhta lack virtually any vertical or horizontal corrolary. My use of the
above boundary split was based on the same dates that imply a Campanian age for
the Barun Goyot and Nemegt, as the same species of lizard, mammal, and dinosaur
appear to cross from the comformable Barun Goyot/Nemegt to the underlying
Djadokhta; some have also suggested that the Djadokhta may be partially
overlapping of the Barun Goyot based on these faunal relationships. Gao and
Norell summarize in their 2001 synopsis of lizard fauna.

<But still more closely related to Tyrannosaurus than any Campanian or Horseshoe
Canyon tyrannosaur.>

  Currie et al. (2003) suggest that the following topology is more likely to be
true:

--+--+--Albertosaurus
  |  `--Gorgosaurus (= Albertosaurus?)
  `--+--+--Daspletosaurus
     |  `--+--Alioramus (= Tarbosaurus?)
     |     `--Tarbosaurus (= Tyrannosaurus?)
     `--+--Nanotyrannus (= Tyrannosaurus?)
        `--Tyrannosaurus

  Which throws a moneky wrench in the use of *Tarbosaurus* as a 1:1 corrollary
to *Tyrannosaurus*

<IIRC T.Holtz indicated that all known Daspletosaurus specimens are of Campanian
age. Btw, an Albertosaurus bonebed occurs at the top of unit 4. The larger
tyrannosaurs apparently hadn't yet appeared by then, rather late in Horseshoe
Canyon time.>

  This doesn't affect the above topology, which implies then that the
Tarbosaur/Tyrannosaur split was in the Campanian, and the use of the Nemgetian
as Maastrichtian supported by the Tarbosaur/Tyrannosaur association is false. Is
it? Or are we choosing that a particular data set will be more right to agree
with the biostrat opinions?

<I think the Nemegt is probably coeval with unit 5 or uppermost Horseshoe
Canyon.>

  But this is not based on any 1:1 correlated stratigraphy, but an asusmption
based on biostrat comparability. Dealt with in other posts.

<Very few if any mammals are known from the Nemegt, and not many lizards. Again,
even the Djadokhtan beds now appear to be of late Campanian age c 73 Ma-based on
dating of "Chuluut Uul"- so there is no way the far overlying Nemegt could be
that old.>

  There are a substantian number of lizard and mammal species between the Nemegt
and various NA formations from the Campanian and Maastrichtian, including
*Mesodma* and *Gobiconodon.* That relative rarity in the Nemegt is probably
related (as has been pointed out before) the tendency of the Nemegt to preserve
large skeletons, and smaller animals are much less complete, if found.

  Cheers,

  Jaime A. Headden

  Little steps are often the hardest to take. We are too used to making leaps in
the face of adversity, that a simple skip is so hard to do.  We should all learn
to walk soft, walk small, see the world around us rather than zoom by it.

  "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)