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Re: Latest K dinosaurian diversity trends (was Re: Titanoceratops, giant ceratopsian from New Mexico)
One of the problems that we have is that we need a better term than
"diversity", that incorporates time. To me, "diversity" refers to the number
taxa present at a single point in time (ie. contemporaneous). There is no
evidence for diversity in the centrosaurinae (for example) as none of the taxa
overlap (although this may be set to change slightly).
Tom Holtz wrote:
>... the high-resolution GIS data of dig sites ... is showing that many
>species of the same
faunal stage/NALMA/whatever you want to call it are NOT contemporaries at
all. Instead, they are falling in distinct very short phases. So it may
well be that throughout the Campanian and Maastrichtian (for instance)
there was never more than one or two comtemporaneous centrosaurine species
in the same region, only one or two chasmosaurines, etc.
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
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
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.
In this respect, the lumping of Hell Creek taxa etc that Jack et al are doing
doesn't change the situation, it just affects the diversity multiplier. The
number of clades present close to the K-T is definitely reduced from what was
seen in the Campanian. Something (maybe) is causing a drop-off in this
through to the Late Maast
plenty of dino taxa in the Hell Creek Fm to go bang at the end (nod to the
catastrophists). Or are there?
For whatever reason DML keeps truncating occasional sentences that I write. no
idea why. I tried various formats and it seems to happen anyway, just so you
know it isn't me being inept! or at least not knowingly.