Late Cretaceous Diversity (quoting from BBC THEROPOD PROGRAMME)

["philidor11" <philidor11@snet.net>]

<First part of the documentary concentrated on Late Cretaceous faunal
provincalism - they... wrongly emphasised the point that South America was,
in terms of fauna, a unique continent.  Of course South America was more
likely 'normal': it's North America that was weird.>

Remembering a prior posting, much of the study of late Cretaceous diversity
has been based on analysis of North America.  When you're looking at the
question of whether the number of species was declining as part of the
discussion of  the impact hypothesis, would you consider observations based
on North America compelling?
Thanks.