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Re: Nemegt and Wangshi etc



Tim Donovan wrote:

> Protoceratopsid remains are also known from the Wangshi; Bayan Mandahu-a
> Djadokhta correlative- has them as well as Pinacosaurus in common.

Although I agree with HP Leahy that radiometric dating is a sure-fire way of
correlating stratigraphhic units (I am less impressed with
magnetostratigraphy, but that's another issue), I don't completely
disapprove of vertebrate biostrat as a tentative SUGGESTION, when you find
unequivocal species correlations. However, you are no longer invoking
SPECIES co-occurrences, or even "GENUS" co-occurences (which, with dinos,
often means the same thing), you are now invoking the co-occurrence of a
rather diverse [putative] CLADE? Even ignoring the question of quality of
evidence (what IS the evidence?), protoceratopsians occur in "Judithian,"
"Edmontonian" and "Lancian" deposits in North America, and units in Asia...
I hardly think this "clade" provides a convincing biostratigraphic
correlation.

BTW: What is the reference for "protoceratopsids" in the Wangshi?


>    The Nemegt fauna apparently extended well beyond the Nemegt basin, and
> not just outer units like Gurilin Tsav.  The Dinosauria mentioned an
unnamed
> unit in Heilongjiang i.e. not the Tsagayan, but very close, with
Saurolophus
> "kryschtofovici" and "A. periculosus", considered of Nemegtian age by
Lucas.

1) Let's not bring Lucas' biostratigraphic schema into this. I'd like to
stick to the facts as published, without relying on a particular worker's...
unique interpretation.
2) I just whipped past the "Saurolophus kryschtofovici" question about a
year back... I believe the specimen is a fragmentary ischium... hardly the
basis for a "genus" level referral. Also, I may well be wrong, but I seem to
recall that the ischium in question was "booted!"

What taxon is the "A." in "A. periculosus", please? And what, I wonder, is
the evidence for its presence?

> This suggests the differences between the Nemegt and Tsagayan were the
> result of time or succession, not distance.
    Actually, this suggests nothing, other than people trying to do the best
they can with very little data. You really should be wary of the distinction
between primary data and interpretation: often, exposition regarding the
implication of new fossil finds borders on speculation, especially when a
new find represents a move from no data to at least some data. You should
rely on the primary data, not the author's conclusions, in trying to
evaluate something as complex as biogeography (or phylogeny, or just about
anything else in science, actually).

>   Yes, Euoplocephalus and Edmontonia persisted from the Judithian to the
> Edmontonian, despite obvious environmental changes as the area became more
> inland with regression. (I don't think faunal changes were yet great;
> generally there was continuity until the Lancian.)
    How do you define continuity? I would say that there was a substantial
change in species representation, at least among hadrosaurs and
ceratopsians. There also appears to have been much less faunal change from
the "Juditho-Edomontonian" to the "Lancian" in southern regions... look at
the presence of Campanian sauropods in Arizona (if not New Mexico).

> In contrast, I don't know
> of any environmental changes in the Barungoyotian areas adjacent to
> Nemegtian ones, by the time of the Nemegt deposition, but the once
> ubiquitous Pinacosaurus is apparently absent in those habitats.
    Is this statement made in reference to a prolonged, personal study of
the uppermost Cretaceous section in Mongolia, or is this conclusion (say)
literature based? Can you characterize the sedimentological and
stratigraphic criteria you used to reach this conclusion? Can you direct me
to a series of papers that support your conclusion? Not that I disagree with
you, I am just curious as to the basis of your statements... what is the
EVIDENCE?


>   True, different NA hadrosaurs preferred different regions e.g. the near
> marine Edmontosaurus and lambeosaurs farther inland. I note, however, that
[...]
    Well, that's the idea, anyway, but I wouldn't characterize this as
"truth." If you know of any hard EVIDENCE for this, I for one will do
backflips.


> [...] Saurolophus and Hypacrosaurus? (=Barsboldia?) [...]
    I don't think so, FYI. I certainly wouldn't base any further conclusions
on this. At least not till more material is collected.


> [...] extended from NA all the way
> to Asia. I can't understand why none of the Tsagayan hadrosaurs-probably
> essentially those of the Wangshi series-were present in the Nemegtian
areas.
    Again, do you suppose that the environment in the Nemegt might have been
more similar to that in North American regions harboring Saurolophus than
Chinese environments harboring the Wangshi fauna? What was the
environment(s) in which the Wangshi was deposited? LOOK IT UP, then consider
your arguments in light of the data.


> Why just the American immigrants? After all, there were hadrosaurs in
> Mongolia in the Barungoyotian period which preceded he c Edmontonian age
of
> Saurolophus. I get the impression the Asian hadrosaurs (which seem
primitive
> to Godefroit) must have been supplanted.
    Our understanding of the phylogeny and distribution of Asian hadrosaurs
is still FAR too incomplete to say anything remotely like this. Again, be
wary of sweeping generalizations thrown in at the end of papers: think of
them as a guide for further research, not a hard-and-fast conclusion.

I'm not sure Rob Gay wanted to shut down *this* particular sub-thread, but I
have to say that I don't see this going anywhere. While I can't say I'm 100%
on top of the data (my attention has been elsewhere, unfortunately), I
believe I have stayed fairly current on this subject. I don't see any
EVIDENCE for the correlations you are making, and the conclusions you are
drawing from them. Go back and examine the raw data, and the methodology
involved (stratigraphy, sedimentology, and the basic assumptions of
vertebrate paleontology). If you feel your hypotheses survive this test,
then bring them back and we can wrassle! :)

Wagner