Re: Catastrophic Extinction?

[Stan Friesen <swf@ElSegundoCA.ATTGIS.COM>]

 From: tholtz@geochange.er.usgs.gov (Tom Holtz)
 > 
 > As shown by various studies, there is no apparent decline (at least at the
 > family level) within dinosaurian populations during the last ~3 million
 > years in western North America - i.e., the Lancian fauna appears to be
 > stable over its duration.

Even at the species level it seems pretty stable.
[Though for the rarer species there is no good way of telling
what their time range really was].

 > ... some groups ...
 > are very rare (1 or 2 species) during the early Maastrichtian and absent
 > during the late Maastrichtian.  The absence in the late Maastrichtian
 > cannot be easily explained by alledged depositional-environmental bias,
 > since the late Maastrichtian is represented by nearly as many localities
 > and more diverse (not less diverse) paleoenvironments than the late
 > Campanian.

And keeping in mind that the Lance and Lance-equivalent beds of
North America are amoung the most thoroughly sampled dinosaur
beds in the world, it seems pretty secure to say formerly common
forms like Hypacrosaurus were *not* there.

[The more southern US Late Maastrichtian beds are less extensive
and less fossiliferous, so some of these forms *could* have
survived there, but no evidence has been found of this].

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.