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RE: Triceratops survived till very end of Cretaceous (citation)

The infamous "3 m gap" is most likely a taphonomic artifact, as the paleosols 
of the uppermost Hell Creek Fm
are too acidic to preserve bone.  See the ref below:

Retallack, G.J., Leahy, G.D., and Spoon, M.D. (1987). Evidence from 
paleosols for ecosystem changes across the 
Cretaceous/Tertiary boundary in eastern Montana. Geology 15:1090-1093.

Guy Leahy

> Date: Wed, 13 Jul 2011 14:27:33 -0400
> From: bh480@scn.org
> To: dinosaur@usc.edu
> Subject: Re: Triceratops survived till very end of Cretaceous (citation)
> From: Ben Creisler
> bh480@scn.org
> Here's the full citation for the article about the discovery of a
> Triceratops horn right under the K/Pg (K-T) boundary.
> Tyler R. Lyson, Antoine Bercovici, Stephen G. B. Chester, Eric J. Sargis,
> Dean Pearson and Walter G. Joyce (2011)
> Dinosaur extinction: closing the '3 m gap'.
> Biology Letters (advance online publication)
> doi: 10.1098/rsbl.2011.0470
> http://rsbl.royalsocietypublishing.org/content/early/2011/06/29/rsbl.2011.04
> 70.abstract
> Abstract
> Modern debate regarding the extinction of non-avian dinosaurs was ignited
> by the publication of the Cretaceous-Tertiary (K-T) asteroid impact theory
> and has seen 30 years of dispute over the position of the stratigraphically
> youngest in situ dinosaur. A zone devoid of dinosaur fossils reported from
> the last 3 m of the Upper Cretaceous, coined the '3 m gap', has helped
> drive controversy. Here, we report the discovery of the stratigraphically
> youngest in situ dinosaur specimen: a ceratopsian brow horn found in a
> poorly rooted, silty, mudstone floodplain deposit located no more than 13
> cm below the palynologically defined boundary. The K-T boundary is
> identified using three criteria: (i) decrease in Cretaceous palynomorphs
> without subsequent recovery, (ii) the existence of a 'fern spike', and
> (iii) correlation to a nearby stratigraphic section where primary
> extraterrestrial impact markers are present (e.g. iridium anomaly,
> spherules, shocked quartz). The in situ specimen demonstrates that a gap
> devoid of non-avian dinosaur fossils does not exist and is inconsistent
> with the hypothesis that non-avian dinosaurs were extinct prior to the K-T
> boundary impact event.
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