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Re: Age of the Amur region, and the Horseshoe Canyon and Javelina formations (was: Re: Age of formations)



Jonathan R. Wagner wrote:

>       "-How good is the evidence for a late Maastrichtian age for the
> Javelina?"
>
>     Good. Not perfect, but good. It is based partially on the
uninterrupted
> sedimentary sequence at the top of the formation which *definitely* spans
> the boundary... If there is an hiatus anywhere, it is between the Aguja
and
> Javelina (not very likely, though). There is a biostratigraphic
correlation
> with the better constrained Naashoibito Member of the Kirtland Shale
> (bracketted radiometrically and correlated with mammals) and the North
Horn
> Formation (The dates for which have been constrained, I can't recall how)
> based on Alamosaurus. Not that I am very comfortable with that. The
presence
> of specimens referable to Torosaurus is a little more damning, in my
> opinion.

The specimens referable to Torosaurus are pretty scrappy, at best. The
Javelina Formation material includes an incomplete parietal and a
postorbital horn core that resembles that of every other large
chasmosaurine. For that matter, I am skeptical of nearly all of the
southwestern ceratopsid material that's being called "Torosaurus." Restudy
of those specimens is now underway. In all, I won't be convinced of the
presence of Torosaurus south of Utah until we get some good, complete skulls
(aside from the McRae Formation specimen. . .that does look pretty
Torosaurus-like).

Andy
_______________________________
Andrew A. Farke
South Dakota School of Mines and Technology, Box P404
501 East St. Joseph Street
Rapid City, SD  57701

605-394-2816

andyfarke@hotmail.com
----- Original Message -----
From: "Jonathan R. Wagner" <jonathan.r.wagner@mail.utexas.edu>
To: <KELL00BELL@aol.com>
Cc: <dinosaur@usc.edu>; <tholtz@geol.umd.edu>
Sent: Wednesday, November 28, 2001 1:27 PM
Subject: Age of the Amur region, and the Horseshoe Canyon and Javelina
formations (was: Re: Age of formations)


> KELL00BELL@aol.com wrote:
>
> "Palynomorphs are said to correlate the Tsagayan with the Wodehousia spina
ta
> palynozone in NA.  Is a Lancian age necessarily implied, or certain?"
>
>     Not sure where Tsayagan is... The idea, put forth by Godefroit et al.
> (2000), is that the Wodehousia spinata Zone in North America corresponds
to
> "Lancian" time, so the presence of that species in Asian rocks indicates
> those rocks are Lancian. This is a misinterpretation of Markevitch's
(1994)
> zonation, in which Wodehousia spinata occurs as part of a zone
representing
> Early Maastrichtian time in Russia (palynomorphs are nasty about showing
up
> at different times in different places). Markevitch et al. (2000) later
> interpreted the Amur faunas as representing "middle" Maastrichtian. How
this
> relates to the Eurpoean stages, or North American stratigraphy, is not
> clear, so I am inclined to default to Markevitch's earlier conclusion. So,
> long story short, don't try to use pollen on one continent to correlate to
> another... be very skeptical of palynologically correlated "Lancian"
faunas
> in Asia.
>
> -------------------------------------------------
>
>       "-Does a Late Maastrichtian age for the Nemegt seem likely now,
[...]"
>     [Other stuff about the Age of the Horsehoe Canyon excerpted]
>
>     OK, you may be making a mountain out of a molehill:
>
>     Vertical succession of faunas does not imply discontinuity.
Dinosaurian
> faunas show some evidence of altitudinal segregation, with putative
"upland"
> faunas looking rather different from "lowland" faunas. In a progradational
> sequence, such as the Horseshoe Canyon Formation, inland facies overly
> shoreline facies... thus, going up vertically in section you are crossing
> "space" as well as "time." Therefore, it is not entirely out of wack to
> interpret the "distinct" Campanian and Edmontonian faunas of the Horseshoe
> Canyon Formation as contemporaries, even if we only have sequential
records
> of them (see my next point).
>
>     The Campanian/ Maastrichtian boundary is not a magical barrier to
faunal
> continuity, it is an arbitrary level in a series of strata somewhere in
> Europe. Recent revision has messed up our traditional, happy view of
> "Judithian" faunas as Late Campanian and "Edmontonian" faunas as Early
> Maastrichtian... it turns out the C/M stage boundary of the European
system
> is probably somewhere within "Edmontonian" time. The "Edmontonian" of our
> youths is now a bastard child of two stages... this does not oblige us to
> treat its faunas as any more different than we did before. The faunal
> heterogeneity of the Horseshoe Canyon Formation has been known for
decades,
> and the usual explanation (that I have read, anyway), is facies-based.
>
>     That said, Anchiceratops *has* been found in "Judithian" rocks. Poop!
>
>     Now, as for the Nemegt, I have always suspected it to be of
> "Edmontonian" age. As I recall, Radiometric dates in the Russian Dinosaurs
> book seem to confirm this, although I don't have the book handy to double
> check.
>
> ----------------------------------------------------
>
>       "-How good is the evidence for a late Maastrichtian age for the
> Javelina?"
>
>     Good. Not perfect, but good. It is based partially on the
uninterrupted
> sedimentary sequence at the top of the formation which *definitely* spans
> the boundary... If there is an hiatus anywhere, it is between the Aguja
and
> Javelina (not very likely, though). There is a biostratigraphic
correlation
> with the better constrained Naashoibito Member of the Kirtland Shale
> (bracketted radiometrically and correlated with mammals) and the North
Horn
> Formation (The dates for which have been constrained, I can't recall how)
> based on Alamosaurus. Not that I am very comfortable with that. The
presence
> of specimens referable to Torosaurus is a little more damning, in my
> opinion.
>
>     "Does Javelina material eg TMM41436-1, suggest a smaller, hence
earlier
> tyrannosaur? "
>
>     I had the opportunity to discuss this specimen with Dr. Molnar at SVP.
> He stands by his assertion that it is not T. rex. I feel we should regard
it
> as Theropoda incerta sedis until such time as a proper study can be
> conducted. In other words: ignore it.
>
>     Hope this helps! :)
>
>     Wagner
>
>
> REFERENCES:
>
> GODEFROIT, P. ZAN S. AND JIN L. 2000. Charonosaurus jiayinensis n.g.,
n.sp.,
> a lambeosaurine dinosaur from the Late Maastrichtian of northeastern
China.
> Compte Rendu de l'Academie du Sciences Naturelles, Paris, series 2,
Sciences
> de la Terre et des planétes, 330:875-882.
>
> MARKEVITCH, V. S. 1994. Palynological zonation of the continental
Cretaceous
> and lower [sic] Tertiary of eastern Russia. Cretaceous Research,
15:165-177.
>
> MARKEVITCH, V. S., E. V. BUGADEVA AND Y. L. BOLOTSKY. 2000. Playnological
> evidence of vegetational change and dinosaur exitinction in the Amur
Region.
> Paleontological Journal, 34 (Supp. 1): S50-S53.
>
>