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Re: Ankylosaurs & Nodosaurs



>A thought struck me the other day; most nodosaurs dies out in the
>early Cretaceous, right? It seems that ankylosaurs were advanced
>relatives, if not off-set descendants of the nodosaurs. Why then,
>were there nodosaurs, and big ones, like Edmontonia, still around at
>the end of the dinosaur reign with the likes of Euplocephalus and
>Ankylosaurus? What advantage did nodosaurs have over ankylosaurs?

Your initial premise is not correct.  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.  This
group seems to be strictly Late Jurassic to Early Cretaceous at first, but I
wouldn't be surprised if Middle Jurassic _Tianchisaurus_ turns out to be a
polacanthid.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661