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Re: New dinosaur diversity articles



> The data do not
> suggest that dinosaurs were decreasing in richness
> leading to extinction
> during the last 10 m.y. of the Cretaceous.

  Lambeosaurs appear far less diverse in North America
by the early Maastrichtian. Hypacrosaurus is the only
post Campanian NA lambeosaur genus known AFAIK. *
Centrosaurines were also down to one genus by
then-Pachyrhinosaurus-and were totally gone by the
late Maastrichtian. Saurolophines had also vanished by
then. The recent Ankylosaurus paper claimed that
ankylosaurs disappeared before the end. That may not
have been true of Ankylosaurus, since  specimens are
stratigraphically high, and one occurs right below the
K-T according to Wroblewski's data. Edmontonia,
however, may have disappeared before the end.



> Refinement of the dating of
> dinosaur fossils, rather than the collection of more
> dinosaurs, is the best
> way to resolve globally the rate of the
> Cretaceous-Tertiary dinosaur
> extinction.

  IMO it is very important to determine which unit is
younger, the Nemegt or the Tsagayan. If Godefroit is
right and the Tsagayan is younger i.e. late
Maastrichtian, that would certainly argue against a
decline in diversity. If the Nemegt is younger, that
would suggest hadrosaur diversity declined in Asia as
well as in North America.
 
* Hypacrosaurus may have persisted into Hell Creek
time but its putative remains are stratigraphically
low and rare, suggesting that it was on the verge of
disappearing. AFAIK lambeosaur remains are not known
from the Scollard, which is equivalent to the upper
Hell Creek, and representative of a more inland
environment favored by lambeosaurs.



                
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