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Dinosaur diversity



A while ago I asked how many species are currently recognised for the 
genus _Triceratops_.  It's a fairly esoteric question, and probably 
no-one really knows exactly.  But, it's probably more than just a 
matter for taxonomy.

A lot of authors have pointed to a loss of dinosaur diversity in the 
final few million years of the Mesozoic as evidence for a gradual 
decline before their final extinction, rather than a single great
catastrophe at the K/T boundary.  In other words, late Maastrichtian 
sites (particularly in North America) are said by some to be dominated 
by large numbers of fossils of a few species, while in
stratigraphically earlier sites, species are represented by less 
fossil material, but there larger numbers of species per site.

But this "loss of diversity" could be an artifact of taxonomy.  For 
example, in western North America, _Triceratops horridus_ is said to 
be the dominant ceratopsian during the late Maastrichtian.  But this 
taxon could embrace a number of _Triceratops_-like species (or even 
genera, like _Diceratops_ or _Ugrosaurus_).  Similarly, there could be 
at least three _Tyrannosaurus_-like genera in the latest Maastrichtian 
- _Tyrannosaurus_, _Dinotyrannus_, _Nanotyrannus_ - rather than just 
one genus and species (_T. rex_).

Any ideas??  Is this a load of @#$@#?