Dear All
I�m hoping you can advise me on an appropriate test of trait-dependence for an
entirely extinct clade.
I want to look at the evolution of body size in ostracoderms - the palaeozoic
armoured jawless fish. A number of ostracoderm clades show an apparent increase
in body size through the Devonian. This is taken as a classic example of
'Cope's Rule' and has also been linked to competition with / predation by jawed
vertebrates.
I have some dated trees for a couple of the most diverse ostracoderm clades.
Each tree consists of around 100 taxa (this might not sound like a lot, but is
actually around 25% of the total known diversity). I've also got a keen MSc
student ready to collect body sizes for these groups, potentially using some
nice 3D models to get volume estimates.
I had initially thought to use �quasse� to model body-size dependent
speciation and extinction rates, but after some digging it seems like this only
works for ultrametric trees. Is there a nice statical way of testing whether
bodysize is correlated with extinction or speciation given a tree comprising
100% fossils? My hypothesis is that extinction is more likely in ostracoderms
with small body sizes.
Any help you can provide would be hugely appreciated!
All the best
Joe Keating
Dr Joseph Keating
Palaeobiology Research Group
University of Bristol
Bristol Life Sciences Building
24 Tyndall Avenue
Bristol
BS8 1TQ
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