[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: New dinosaur diversity articles



--- "Jaime A. Headden" <qilongia@yahoo.com> wrote:

> Tim Donovan (uwrk2@yahoo.com) wrote:
> 
> <The point is that diversity did decline prior to
> the end, indicating that
> other factors* were at work causing extinction.>
> 
>   Tim has yet to prove this, or even show it's
> likely, without using a
> small set of a lineage (only lambeosaurs? why not
> use hadrosaurs?

  I mentioned Saurolophus, not just lambeosaurs.



 
> Tim cannot prove his gradual
> reduction in species without
> using a small group of dinosaurs from ONE continent,
> as I have yet to see
> a globally correllated example from him.

  Some taxa e.g. centrosaurines, were only known from
one continent but appear totally extirpated in all
late Maastrichtian NA environments. Only
chasmosaurines are known from lowland and intermontane
environments by the Lancian. This was a large
geographical area, not a forest. See Dodson's remarks
in The Complete Dinosaur. The idea of gradual
extinction is not new.

> 
> <Someone suggested the edmontosaurs/anatotitan
> "mastered" the lambeosaurs
> by the late Maastrichtian.>
> 
> Because there are fewer lambeosaurs
> and more hadrosaurines
> in the Maastrichtian, and to use Tim's favored model
> for pterosaur
> extinction,

  I said nothing about pterosaurs.



> they were "outcompeted" by their
> longer-jawed, larger, more
> efficient hadrosaurine relatives. I do not think
> they were,

  Nor I, that was the point I tried to make, below.




 as I think
> Marjanovic used the flavor of competition, I simply
> attempted to explain
> how more hadrosaurines are known from Maastrichtian
> NA than
> lambeosaurines, as a refutation that diversity was
> shrinking.


 Diversity declined even among hadrosaurines in NA;
Saurolophus vanished by late Maastrichtian.



 Rather, one
> group is replaced by another in the selected area of
> investrigation (there
> were plenty of Maastrichtian lambeosaurs in Asia,

  Not necessarily of late Maastrichtian age, when the
bulk of diversity decline occurred. Previously it was
mentined onlist that Godefroit's proposed late
Maastrichtian age for the Tsagayan reflected a
misinterpretation of Wodehousia, which represented the
early Maastrichtian of Russia.



> and likely in Europe as
> well,

  Pararhabdodon was not a lambeosaur.



> but it appears fewer hadrosaurines given the
> brevity in the Nemegt


 Saurolophus was an abundant hadrosaurine; the
lambeosaur Barsboldia was very rare. What do you mean
"brevity in the Nemegt"? Paleomag results suggest it
lasted over a million years.


 
> <I doubt it. Edmontosaurus already existed in the
> late Campanian,
> apparently in near coastal environments which
> excluded lambeosaurs.
> Farther inland, Hypacrosaurus was still abundant
> about 3 million years
> later. Ankylosaurids and nodosaurs also appear
> ecologically separated.>
> 
>   This proves very little. Prior occurance of
> hadrosaurines to
> lambeosaurine diminishment is simply a factor of
> lineages of sister-taxa
> occupying the same strata and altering geography
> together. Take the
> changing climate: in the Maastrichtian, we see the
> climate shift from the
> "bayou"-like wetlands into a drier, less-bushy
> Okavango-like floodplain.

  Then why did Edmontosaurus fare better than those
adapted to a drier climate?



> Suddenly, animals used to browsing must make way for
> grazers. Smaller size
> for travelling dense vegetation at times makes way
> for huge size for open
> areas, high-browsing shifts to low-browsing and the
> Late Cretaceous
> version of grazing: fern-munching. Even a Savuti
> lion still pauses at a
> bull elephant, so a *Triceratops* would make a
> formidible foe to even an
> animal 1.5 times bigger than it (I am, of course,
> speaking of
> *Tyrannosaurus*).
> 
>   So as climate shifts, we will SEE animals change,
> populations shift, and
> new animals take precedence over the old. Using the
> old population for the
> underlying strata to prove diversity issues for the
> whole ignores the rest
> of the biome.
> 
>   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)
> 
> 
>               
> _______________________________
> Do you Yahoo!?
> Express yourself with Y! Messenger! Free. Download
> now. 
> http://messenger.yahoo.com
> 


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com