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Re: Latest K dinosaurian diversity trends (was Re: Titanoceratops, giant ceratopsian from New Mexico)



2011/1/1 Denver Fowler <df9465@yahoo.co.uk>:

> Right. This does reduce the number of taxa at any given point, but it doesn't
> radically alter the drop in diversity towards the K-T. My view would be that 
> we
> only have one chasmosaurine lineage in the Late Maastrichtian, whereas other
> people might think there are 3 or 4. However, we all agree that there is only
> one clade (the Triceratops clade) whereas there used to be at least 3 
> ceratopsid
> clades in the Campanian (possibly even more: another talk at SVP that was
> genuinely exciting). The same situation with hadrosaurs: you can split the 
> only
> North American Late Maastrichtian hadrosaurid (Edmontosaurus) into 3 taxa if 
> you
> like, but it's still only the one clade, whereas in the Campanian we had
> multiple clades (3-4 hadrosaurines, 3-4 lambeosaurines). So diversity is just
> modified by a multiplier depending on whether you are a splitter or not.

But, supposing you have some splitter dividing Edmontosaurus in 6-8
different taxa (which also would be lineages or clades) you would not
infer there was a reduction in the number of clades independently of
the lumping-splitting disjunctive. I think you would have less clades
originated in the Campanian or earlier, but not necessarily more
clades (I mean, clades originated in whatever moment). And, as long as
we refer to the number of clades originating previously to a given
period, if my logic is right, they will always be greater in the
immediately previous period than in the first mentioned (and
temporally later) period, as long as we accept the existence of
extinctions between both times, regardless of the actual total
diversity of each period (I am not sure this sentence is clear). This
partially explains why you have a greater diversity of phyla in the
Cambrian (produced by earlier cladogeneses) than in subsequent
periods.