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Re: Age of the Djadok(ht)a, Barun Goyot and Nemegt Formations
--- "Jaime A. Headden" <email@example.com> wrote:
> Isn't it just totally wicked that we only need ONE
> taxon to prove the age of
> a formation, sans other data?
Age estimates are again, based on more than that.
> 1. It as with other parasaurolophines are index
> taxa relative to the
>thus constraining their appearance to
> that stage regardless of
> formation. Based on the number of *Parasaurolophus*
> specimens (RARE) and even
> the "parasaurolophine" *Charonosaurus*, we are given
> to doubt a lot of index
> categorization without ample fossil material to
> express to ourselves the ages
> of these taxa. Similarly, reports of Campanian
> *Parasaurolophus* will need to
> be confirmed, but since *Parasaurolophus* is an
> upper Maastrichtian fossil,
> it's unlikely there ARE Campanian *Parasaurolophus*
WTF ??? Do you think the Kaiparowits and De-na-zin
are of Maastrichtian age? ALL known North American
parasaurolophines are of Campanian age. Williamson has
repeatedly pointed out that Parasaurolophus does NOT
occur in the Naashoibito.
> just as it is unlikely the
> formation, if it IS *Parasaurolophus*, is Campanian
> but is in fact
> Maastrichtian. We might also just call
> *Charonosaurus* a species of
> *Parasaurolophus* since their time period can now be
> nailed down as the very
In fact, the apparent restriction of North American
parasaurolophines to the Campanian, coupled with
biogeographic links between Asia and America, is one
reason I doubt Godefroit's age estimate for the
> and can now use *Parasaurolophus* as an even
> better index genus.
For the PRE-Maastrichtian or Campanian IMO.
> 2. Parasaurolophines evolved in Asia and dispersed
> to North America, so that
> Mongolian PIN 3458/5 represents the earliest
Buffetaut considered Tsintaosaurus a
parasaurolophine, and it occurs in Djadokhta
equivalent beds (Campanian).
> *Charonosaurus* the next in lower Maastrichtian
> Tsagayan deposits in the Amür
> region, and finally Maastrichtian *Parasaurolophus*.
> If this is true, then its
> possible the older specimens of *Parasaurolophus*
> represent possible
> transistory taxa or even *Charonosaurus* in North
> America. Gasp! Given this, we
> may now have a span of the entire Djadochta, Baruun
> Goyot and Nemegt Formations
> to "never preserve a parasaurolophine".
No, see above, they apparently existed in the
Djadokhtan period, which I suspect was also the age of
> the fossil record is
> currently complete enough to counter this ridiculous
> theory, it is highly
> unlikely that any such scenario is true. Is it?
> And finally, a synthesis:
> 3. Parasaurolophinae is a taxon that spans
> Campano-Maastrichtian times, from
> an apparently middle Campanian or even Santonian
> Baynshiin Tsab (Which has been
> associated with the Djadochta Formation by some)
> into the late Maastrichtian.
> During this time, parasaurolophines are diversifying
> from essential basal Asian
> stock, such as *Tsintaosaurus* or *Jaxartosaurus* or
> something completely more
> odd, appearing in Djadochta or earlier formations,
> and then expanding in size
> and latitude, eventually arriving in the Amür Region
> some time at the beginning
> of the Maastrichtian stage or even earlier, and then
> crossing a Beringian
> exposure into North America
Godefroit suggested a NA origin.
>where it would become
> found from Mexico to Canada
> and spawn even more species. The relative dearth of
> recovery in Asia can then
> be lain at the feet of the more productive
> investigations in North America by
> American, Canadian and Mexican scientists.
> So which, I ask, of all these scenarios, seems
> more likely given the fossils?
Btw isn't it about time somebody corrected the
temporal order of the Asian units in the title of this
thread as well as the spelling? :)
> Yahoo! Mail - PC Magazine Editors' Choice 2005
Yahoo! Mail - PC Magazine Editors' Choice 2005