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

Re: Albertosaurine Survival and the End of the Cretaceous



On Mon, Jun 23, 2008 at 6:31 PM, John Scanlon
<riversleigh@outbackatisa.com.au> wrote:

"Hi Raptorial (if I may use first names),"

Heh heh, just a run-of-the-mill internet moniker. Use whatever variant
you like - all I know is that "Raptorial" has four more letters than
"Talon." But it's your fingers. ; )

"I hope you get some informed responses as well as encouraging ones; I'm no
dinosaur expert but I already find this a more interesting discussion than
the long-running origin-of-flight sideshow. (Cretaceous North-American
biogeography has got somewhat interesting since fossil snakes started
turning up in the Cenomanian, but I still know little about it).
Cheers,
John"

Thank you for that, and now I'm going to go brush up on fossil snakes.

On Tue, Jun 24, 2008 at 6:52 AM, Tim Donovan <uwrk2@yahoo.com> wrote:

" A few comments: Tyrannosaurus rex lived in swampy habitat toward the
end, as there was a local transgression."

Interesting, interesting . . . sort of what I recalled hearing
regarding *Edmontosaurus*. Good to know.

"But there is no evidence of an
albertosaur/lambeosaur/centrosaurine/nodosaur comeback."

Well, of course, aside from my whole notion ultimately being
conjecture, I didn't actually say anything about a "comeback." What I
was really getting at was more along the lines of *refugia* - that the
albertosaurine complex became *restricted* to coastal and/or cooler,
higher-latitude regions while the tyrannosaurine complex expanded and
became fully dominant in former albertosaurine territory. That is to
say, my concept here is that inadequate sampling in the east, or in
northern Canada/Alaska, may be the reason we have not yet found
late-Maastrichtian albertosaurines - rather than a true, flat-out
absence over all of North America. So that's what I'm trying to get
clarified/confirmed/denied.

Although, as you stated, tyrannosaurines lived in swampy areas to the
exlcusion of albertosaurines in the latest Cretaceous American
northwest, so now any discussion would be about more northerly
latitudes as the conjectural refugium. Has any tyrannosaurine material
ever been reported from Alaska, and how certain are we that the
Alaskan albertosaurine material really is exactly that?

"As for Asia, the late Maastrichtian age of the lambeosaur dominated
Udurchukan, proposed by Goedefroit et al on the basis of palynomorphs,
is not certain."

Hm, interesting once again; any papers out there that explain why such
a date is uncertain? I'm assuming that some sort of plant-migration
thing (the plant groups of late Maastrichtian America being present at
an earlier time in Asia) is involved . . . or not. *shrugs*

"IMO the transition from Albertosaurus to T. rex reflected
continent-wide, predator-prey escalation not changing topography."

Well, I can say that this would make sense in and of itself (certainly
can't ignore that kind of competitor), but the simultaneous loss of
the centrosaurines, nodosaurs, and most/all lambeosaurs suggests that
some wider ecological effect was in play - some effect to which *T.
rex* was probably responding via increased body size, just like what
seems to have happened with *Edmontosaurus* and *Triceratops*, as
additional examples. I had been under the impression that the
regression of the Western Interior Seaway and the resulting
drier/less-stable continental interior was to blame, but I guess it
must have been more complex than just that.

"best,

Tim"

Thanks for the response - some good food for thought there.