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Tim Donovon (sirius531@yahoo.com) wrote:

<Jaime didn't address my point about the implication of the dating of "Chuluut

  This was probably because I washed over the second in my cut and pasting of
the text in my reply.

<Absolute dating is the best way to determine the ages of Gobi formations. The
Nemegt lacks datable materials, but Shuvalov wrote that the IGEM date of c 75 Ma
for the Barungoyotian beds at "Chuluut Uul" confirms a Maastrichtian age for the
stratigraphically higher Nemegt.>

  And how were these dates arrived at? That is, materials involved, taxa used,

<This view has been strengthened more recently by newer dating indicating a
somewhat younger age-c 73 Ma-for "Chuluut Uul"and the discovery of Pinacosaurus
there, indicating a Djadokhtan age for the locality.>

  Or it's possible *Pinacosaurus* progressed into the younger strata as much as
*Velociraptor* did.

<How could the far overlying Nemegt be as old as Campanian if Djadokhtan strata
are that age?>

  If the use of relative biostrat for assisting dating fails in its consistency,
I can question. However, this appears to be the first time "absolute" dating
measures have been done. But if Shuvalov's dates are not based on absolute or
questionable dating methods (I would love the refs on this) then this date must
be taken with a grain of salt.

<The upper Barungoyotian beds presumably extend into the early Maastrichtian and
the Nemegt should be c mid Maastrichtian.>

  Even if the "upper Barungoyotian" (Barun Goyot Formation, white beds of
Khermeen Tsav/Tsab, etc.) was Maastrichtian, this does not make the Nemegt
middle Nemegtian; a formation can be of any length, after all, and the absence
of absolute datable materials but presence of overwhelming subjective dating
materials makes any implications of its age a little questionable. Allocation of
the "Chuluut Uul" beds notwithstanding. Incidentally, where is this and what's
the geological report on it, or is this the same as the Shuvalov beds?

<Does Carr agree that Tarbosaurus is not most closely related to Tyrannosaurus?>

  Few researchers agree on the composition of these taxa. I think given the
phylogenetic analysis of Currie et al., limited to the cranium and jaw, that
their analysis should be taken with a grain of salt, but that grouping is one of
the best supported clades, even if it is precisely effective as a "different
parts of the skeleton can evolve at different rates than others" issue. New data
brings new surprises and opinions, even in grand researchers. Carr has yet to
perform a study on the phylogeny of tyrannosaurs, but his opinion is based on
comparable osteological features, a perspective I can agree with, but involves
only the cranium.

<There are other hints that the Nemegt is younger, albeit slightly, than the
Horseshoe Canyon e.g. the extreme rarity of Nemegtian lambeosaurs contrasted
with their abundance in unit 4, which suggests the Nemegt is representative of a
slightly later period in which lambeosaurs were greatly diminished if not

  Or that the formation did not support the non-*Saurolophus* levels. The
Nemegtian needs to be better sampled, as even *Barsboldia* is very fragmentary.
A formation also need not bear lambeosaurs just because a North American
Formation does. the Nemegt may have gotten its hadrosaurs _from_ North America,
or given them _to_ North America. However, since some here do not believe a
transition between these two regions did not occur after the onset of the
Campanian, who knows how this will be affected. Tagging fauna as absent/present
may be just as critical as absence of preservation does not mean absence of a
fauna, which is why I caution the use of fauna as dating measures.

  Note: my references are horribly deficient in the order of dating of the
Horseshoe Canyon, etc., and I concern myself more with the small-bodied
vertebrate taxa, such as mammals, lizards, snakes, etc., or whatever happens to
occur there. Similar animals arrive between these regions in "Asiamerica" at
different times, such as the presence of a Nemegtian leptoceratopsid
(*Udanoceratops*), a Judith River one (unnamed, *Leptoceratops* sp.), a
Horseshoe Canyon/St. Mary River one (*Montanoceratops*), and a Lancian one
(*Leptoceratops*), leaving a fair gap among these. Dating some regions can be
just as questionable, as Altan Ula IV, containing *Udanoceratops* and *Avimimus*
has been dated as anywhere from Djadokhtan to Nemegtian in age, questioning
their use as biostrat markers until better information is available.


  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)