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Re: Age of Gobi formations



Tim Donovon (sirius531@yahoo.com) wrote:

<If Ukhaa Tolgod is northeast of Khulsan, in the Nemegt basin, the implication
is that it underlies Khulsan, perhaps considerably, depending on distance.>

  This may or may not be true, but the positional difference must depend on
stratigraphy, not geography. In some places the Morrison can directly underlie
younger members of the Cedar Mountain, whereas in others the older members will
separate the two along with various thicknesses of the inconformity and
Sundance. *shrug*

<IIRC you previously posted that Ukhaa Tolgod lithologically resembles the Barun
Goyot more than the Djadokhta. But lithology varies considerably in outcrops of
Djadokhta age e.g. the lower mudstone layer at Alag Teg is overlain by lighter
sandstone like at Tugrikin Shire.>

  I never described the lithology of Ukhaa Tolgod, but this is largely true.
Lithologically is was wetter than Bayn Dzak, but the fauna have united Ukhaa
Tolgod with the Djadokhta in general, a condition that is prevalent in
literature on the locality.

<Page 261 indicates two dated Barungoyotian localities: Tsaagan Nuur 80 Ma, and
"Chuluut Uul" c 75 Ma.>

  Corresponding to which formations? Barungoyotian, once again, refers to an
"age", not a lithostratigraphic series.

<And the dating is obsolete anyway.>

  The why cite it?

<Shulalov, page 268, united the two.>

  He has yet to be followed. The literature was written and known since 1994,
and still the two are separated by researchers in the region, Mongolian,
Chinese, and Western alike.

<You mean hadrosaur taxon.>

  Not unless I was excluding thyreophores, which I suppose I could have included
for comparison, but it would only serve to muggy the issue: *Barsboldia* is not
a thyreophoran, a clear conclusion based on the dorsal, sacral, and caudal
morphologies.

<Maybe it is pathological.>

  In which case we'd have to support the similar morphology in say, stegosaurs,
would be as likely to be pathological. Successive vertebrae with club-shaped
distal ends, expanded only laterally, in multiple taxa, suggest it is not,
especially as neural pathologies appear to be toward other spines and occur
rather than in a series but in interrupted continuity; that is, they are
unusually notable when they appear, as in one spine in five has this deformity,
rather than the base of the tail as occurs in stegosaurs. I think Osmólska and
Maryanska ruled this out for similar reasons.

<Does it resemble any other roughly contemporaneous hadrosaur to the same or a
greater degree e.g. Amurosaurus?>

  I have not seen the postcrania of *Amurosaurus*, only the described maxilla
and dentary, so I couldn't comment on that.

  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)