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Re: Ankylosaurs & Nodosaurs



> Most nodosaurs did NOT die out in the Early Cretaceous.  As far as
> we know, nodosaurid diversity was never particularly high, but the
> situation in the latest K (Campano-Maastrichtian) does not seem to
> be significantly less diverse than the situation in, say, the
> Barremian, or the Aptian-Albian.  When ankylosaurids appear, they do
> not seem to do so at the expense of nodosaurids.  Futhermore, there
> is a third family, Polacanthidae, to consider here

Again, this depends a lot on the definition of your nodosaurids.  If 
_Polacanthus_ and its relatives are removed from the nodosaurids (as 
the polacanthids) then it cuts down nodosaurid diversity by quite a 
lot.
But, there is also a view that _Edmontonia_, _Panoplosaurus_, and 
other Campano-Maastrichtian nodosaurids which can be defined (among 
other features) by an edentulous premaxilla should be separated as a 
new family, the Edmontoniidae.  That would mean that the nodosaurids 
became completely extinct before the end of the Cretaceous.

Also, whereas ankylosaurids are known from late in the Cretaceous in 
North America (_Ankylosaurus_, _Euoplocephalus_, _Dyoplosaurus_), 
there are no nodosaurids/polacanthids/edmontoniids from the 
Cretaceous of Asia (at least none that I know of).  I think it's fair 
to say that in the Late Cretaceous, ankylosaurids had the upper hand 
over their less heavily-armoured cousins.