RE: Bakker's Brontosaurus and Late Cretaceous populations

[Tim Donovan <uwrk2@yahoo.com>]

--- Denver Fowler <df9465@yahoo.co.uk> wrote:
 
> You can't really state this because there is not a
> enough published material from the North Horn and
> McRae to look at percentages. 

  IIRC Williamson once said the only "Alamosaurus"
from the McRae consisted of a few scraps of large limb
bones, while Lucas mentioned a limb bone.



 
> Toothmarked dino bone is not particularly common in
> the fossil record, and when it is found, is more
> likely indicative of carcass processing, which
> doesn't
> necessarily indicate active predation. I've not seen
> any rehealed injuries for Alamosaurus material, but
> then, I don't recall that many for the whole
> sauropod
> record.


 P. Currie mentioned some. If Morrison theropods
attacked auropods, why not the more powerful T. rex?

 
> That said, bone surface preservation in the
> Naashoibito at least, is not generally good enough
> to
> preserve fine tooth scratches, 


 What about the Javelina and those other units?

 
> >  Maybe at the boundary between the Edmontonian and
> > Lancian. AFAIK, Hypacrosaurus is still abundant in
> > unit 4.


 I meant the upper Horseshoe Canyon formation, where
taxa unknown in the Lancian, Saurolophus and
Hypacrosaurus, were definitely still present. 


> 
> By my understanding, there is no decent evidence of
> Lambeosaurines in North American Lancian strata. The
> only possiblity is Boyd & Ott 2002.


  Boyd said the specimen was found low in the Hell
Creek. Maybe the lowest strata predate the true
Lancian period, just like the Lance frm. exposures in
Park County WY. He did mention Lancian taxa such as
Edmontosaurus, Thescelosaurus etc in the same area but
I'm not sure if they were at the same level as the
apparent lambeosaur.



 
> It's just a hypothetical point but something happens
> pre-Lance/Alamosaurus that shakes up the latest
> Maastrichtian faunas. 


 Definitely.  


>You can hypothesise what that
> is, but the last major (mid-late
> Maastrichtian)regression cycles are pretty severe
> and
> greater in extent than the previous cycles. It
> wouldn't be unreasonable to postulate a
> corresponding
> greater influence on the fauna.


  I don't think the evidence favors regression as the
cause of the Edmontonian-Lancian transition. The
Lancian fauna was more escalated than the Edmontonian
fauna, as well as less diverse. Ankylosaurs and
chasmosaurines became larger, presumably to survive T.
rex. Others may not have fared as well alongside the
new predator. If regression had caused environmental
deterioration e.g. a drier climate and less
vegetation, I don't think the result would be larger
dinosaurs, which were still abundant, especially
Triceratops and Edmontosaurus/Anatotitan. For various
reasons they may have been best able to survive T.
rex, and proliferated in the absence of others not so
fortunate.

 Tim


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