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Re: Fastovsky vs Archibald
On Mon, 27 Jun 2005 03:55:05 -0700 (PDT) Tim Donovan <email@example.com>
> --- Phil Bigelow <firstname.lastname@example.org> wrote
> > The Scollard Fm. may have been deposited far from
> > the WIS. Some workers
> > even claim that the Scollard, itself, had closed off
> > the Seaway.
> But what about the Frenchman, farther east? I don't
> think there is any doubt that the Scollard was farther
> inland than the Hell Creek, and represented a cooler,
> drier environment.
I agree. And the Scollard Fm. should be presumed to be a separate and
unique paleoecosystem at least until proven otherwise by empirical
> > the climate would have
> > been harsher than it
> > was further to the south.
> > The Hell Creek Formation was deposited adjacent to
> > the WIS, which
> > moderated its climate.
> Right. Regarding flora, IIRC Wodehouseia is common to
> both units. But I only wanted to make the point that
> the Scollard has virtually the same dinosaur taxa as
> the Hell Creek, despite environmental differences
> formerly associated with much different hadrosaur
> types. Edmontosaurus was the predominant hadrosaur in
> near marine environments since the Campanian. Other
> taxa lived farther inland.
Isn't _Edmontosaurus_ also found in the Saint Mary River Formation, an
upper floodplain unit which abuts the Laramide uplift?
> The absence of such taxa in
> the inland Scollard suggests they were gone by the
> latest Maastrichtian, causing Edmontosaurus to occupy
> their habitats.
> > Migration away
> > from the Hell Creek region or increased geographical
> > restriction within
> > the Hell Creek region are two equally parsimonious
> > interpretations of
> > that same data, and in theory they are both provable
> > hypotheses.
> Or falsifiable. As I wrote before, Russell suggested
You can't falsify one hypothesis with another hypothesis. ;-)
> that the apparent absence of nodosaurs in upper
> Lancian sediments was due to regression, causing the
> near coastal nodosaurs to abandon the Hell Creek etc,
> and migrate farther eastward with the "receding" sea.
> But how likely does that explanation now appear in
> light of evidence for transgression late in Lancian
At least Russel's hypothesis is testable. Find a North Dakota or South
Dakota section that is in the upper part of the Hell Creek Fm. (say, a
non-marine section that is close to but stratigraphically above the
estuarian Breien Member) and then start searching for articulated
nodosaur remains. If some are found, then Russel's hypothesis becomes
the best one. But if articulated nodos are not found, that doesn't
necessarily mean that his hypothesis has been falsified.
> >But it
> > is nearly impossible to identify an undisputed
> > extinction horizon within
> > a formation.
> Interestingly, Edmontonia disappears in the
> Ferris at the level where a change in sedimentology
> precludes further reworking. It may have been gone
> long before then.
"Gone" in a sense, perhaps. "Extinct", not so sure.
> > All that we can say for certain is that, so far, no
> > articulated nodosaur
> > or lambeosaur skeletons have been collected from the
> > upper part of the
> > Hell Creek Formation.
> Or equivalents, AFAIK.
> > We don't even have enough
> > samples to correlate the
> > known nodosaur occurrences with depositional
> > environments.
> Russell noted long ago that nodosaurs are often found
> in marine sediments.
Which may be reflective of their paleogeographic range, or it may be
reflective of taphonomic concentration. I favor the latter hypothesis.
Nodosaurs (and ankylosaurs) are often found laying on their backs both in
fluvial units and marine units. Maybe they bloated and floated down
rivers like gas-poofed rhinos. In high-output rivers, the carcass could
have been transported hundreds of kilometers to the sea. Their thick
armored hide may have precluded the carcass from bursting. Maybe the
thinner-skinned hadrosaurs' and ceratopsians' stomachs burst open before
their corpses could make it to the sea?