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Re: Reduced Consensus (Was: Afrotheria revisited)
Thanks Mike Taylor for your reply!
"Reduced consensus" sounds about like what I figured had
happened. I looked briefly at the additional information, but have
to look at it more carefully to see if it tells me anything.
Arsinoitherium doesn't seem to have a particularly high proportion of
missing data in their matrix, so it's not quite like your
hypothetical "Eodino". On the other hand, I can think of reasons why
it might be a problem. It was the largest (body mass) of the taxa
they considered, and has famously unusual teeth (long row of
bilophodont postcanines, premolars pretty well molarized, as I
recall, though I haven't looked recently and am not a trained
observer of dental characteristics). So I guessed it would have lots
of special autapomorphies, making it into a LONG BRANCH. And we all
know THEY can be a worry!
I'm still not 100% convinced it isn't cheating: I'm genuinely not
sure. I think there can be legitimate and principled reasons for
excluding taxa, but throwing away data always makes me nervous. Yes
the data matrix gives a well-resolved tree for 22 taxa, but is that
because of "gerrymandering"? Would it be possible to get a DIFFERENT
well-resolved tree by excluding one of the other taxa (this is
something that time and computer power could check!)? I saw no
comment in the paper or supplementary information indicating how
Arsinoitherium was excluded (from tree or from matrix, to raise the
issue David Marjanovic raises) or what the rationale was: some
discussion would have been reassuring.
Micky Mortimer crowed on the DML forum recently about a published
criticism of a paper that had achieved a well-resolved tree by
excluding taxa from consideration: crowed because he had made a
similar criticism some months ago on the forum. I'm hoping he will
comment: does he think Tabuce et al. are doing something good, or bad
like the people he crowed over.
(Does saying "crowed" enough times count as dinosaur relevance?)
I'm rather hoping that Tabuce et al. are in the clear, since
their conclusions appeal to me. Christine Janis and a co-author have
recently (last year?) published a paper in "Journal of Mammalian
Evolution" (called "Spiny Norman and the Garden of Eden") arguing
that a holarctic origin for placentalia is the more parsimonious
hypothesis in terms of the number of vicariance and migration
episodes it postulates, and Zack, Penkrot et al. (last reference in
Tabuce &c's paper) find close Eocene relatives for the Macroscelidea
in North America!
Leading to another mild discomfort I feel about Tabuce &c. They
say they have found the apheliscines to be a sister-taxon of the
Macroscelidea, but their trees actually show Apheliscus as a sister
of Macroscelidea+Paenungulata. I assume this is what their dental
and tarsal characters show: Zack and Pencrot have an above-the-tarsus
character (co-ossification of the distal tibia and fibula) which
would unite Apheliscus with crown Macroscelidea. (I think: I've got
to re-read their paper more carefully.)
Anyway... I'm a non-paleontologist (I'm a philosopher,
specializing in logic) and never confident that I'm saying anything
that REAL paleos will even think deserves COMMENT! I found the
Tabuce &co paper very interesting, I am by no means confident that I
have spotted any real flaws in their work... and I will read with
interest whatever the pros have to say about it!
University of Melbourne