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Re: ?Latest paper on the extinction of dinosaurs in North America
> Dean A. Pearson, Terry Schaefer, Kirk R. Johnson, Douglas J.
> Palynologically calibrated vertebrate record from North Dakota
> with abrupt dinosaur extinction at the Cretaceous-Tertiary boundary,
> 29(1), 39 -- 42 (January 2001)
Yes, that appears to be the latest publication regarding N.A.
> When calibrated to the K-T boundary, occurrences of
> fossils indicate an uppermost Cretaceous barren zone (Fig. 2). Where
> basal Fort Union is Cretaceous, this gap is 1.76 m. At Mud Buttes,
> where the
> K-T boundary and the formational contact are coincident, the gap is
> 2.37 m.
First observed in the Hell Creek Formation by J. David Archibald back in
1982. He was also the first to label it the "barren zone".
Has a similar barren zone been found at the top of the Lance Formation?
> These results differ from Sheehan et al. (2000), who listed a
> minimum of 10
> dinosaur specimens in the uppermost 5 ft (1.52 m) of the formation.
> checked their unpublished data (Sheehan, 2000, written commun.) and
> ascertained that all their vertebrate sites in this interval were
> near Mud
> Buttes, implying that their survey recorded dinosaur fossils where
> we found
Possibly due to having been "picked over" by the previous research team?
How fast does that particular section of outcrop erode? I note that
their respective publication dates are only separated by one year! When
did each team conduct their field work?
> "Our data show that there is a gap below the K-T boundary in our
> study area,
> but it is an interval in which we found no vertebrate fossils of any
> even those of vertebrate groups known to have survived the K-T
> event (e.g., fish, amphibians, turtles, crocodilians).
Phosphate leaching via acid rain?
> It is
> possible that
> this gap is a function of depositional conditions associated with
> formational transition rather than a reflection of true terminal
> faunal diversity.
Also a good possibility. Deposition rates are vastly different between
the Hell Creek formation (high, steady deposition rate) and the Fort
Union formation (lower, variable deposition rate).
> In contrast, Sheehan et al. (2000) reported
> dinosaurs within 1.52 m of the K-T boundary from the southern part
> of our
> study area.
Close, but no seegar.
> Our vertebrate data and those of Lillegraven and Eberle
> (1999) both
> show a diverse, dinosaur-rich fauna in the highest Cretaceous
> a pattern that is consistent with abrupt extinction of
Ooooo. I don't follow.
It's hard to know how long that "barren zone" lasted, and its hard to
know *how* the extinctions proceeded within that barren zone. I guess
the word "abrupt" can be interpreted more than one way in this case.
> Combined with high levels of plant and insect extinction (Johnson et
> 2000), these data support the model of a terminal Cretaceous biotic
> Have I already mentioned the youngest hadrosaur tracks, those
> fossils that are not going to be dissolved by acid rain, in this
> They are 37 cm below the boundary, writes Lockley.
Close, but no seegar.
> Long live the youngest ammonite, found 10 (ten) cm below the
Close, but no se....well, now I'm just being repetitive ;-)
Dont' get me wrong. I believe that the mass extinction (particularly the
terrestrial portion) was abrupt and that it was probably caused by an
impact. I just think that it is hard to prove scientifically.
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