Evidence for dinosaur migration

[ptnorton <ptnorton@suscom-maine.net>]

In reviewing the literature on trackways and monospecific fossil assemblages 
of late Cretaceous North American herbivorous dinosaurs, I come away with 
mixed feelings about the strength of the evidence with respect to the 
hypothesis that these animals moved in migrating herds. It is obviously 
clear that they assembled in large groups for some purpose, but what is the 
evidence that this demonstrates migratory behavior, as opposed to (for 
example) communal gatherings for reproduction or nesting?  I admit my 
references on this topic are a bit dated (back to the late 90's), so if 
anyone could share their thoughts or more recent references to articles on 
this point, I would greatly appreciate it.

Thanks!

PTJN