[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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!

Allen Hazen
Philosophy Department
University of Melbourne