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Re: Age of the Djadok(ht)a, Barun Goyot and Nemegt Formations




--- "Jaime A. Headden" <qilongia@yahoo.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
> Maastrichtian, 


 Absolute nonsense.


>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
> same,

 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
Tsagayan.

> 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
> parasaurolophine, 


 Buffetaut considered Tsintaosaurus a
parasaurolophine, and it occurs in Djadokhta
equivalent beds (Campanian).


>and
> *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 Tsagayan.


>But since
> 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?
> 


 NONE.

 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? :)
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