[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: *Gansus*
>What chance is there that *Gansus* actually belongs into Hesperornithes?
>As explained in their supplementary information, You et al. (2006) found 24
>MPTs, in which *G.* was either outside of (Hesperornithes + Neornithes) or
>closer to Neornithes than *Ichthyornis* or (as in the majority-rule consensus
>tree in the paper itself) closer to (Neornithes + *Ichthyornis*) than to
>Hesperornithes.
>Neither *Enaliornis* nor *Pasquiaornis* (nor, unsurprisingly, *Potamornis*)
>were included; the only representatives of Hesperornithes are *Baptornis* and
>*Hesperornis*. The supp. inf. states that *E.* was excluded because it shows
>hesperornithean autapomorphies and would therefore predictably have come out
>as >the sister-group to *Baptornis* + *Hesperornis* -- but I can't see why
>that's an argument. It would after all have broken up the very long branch
>that leads to (*B.* + *H.*); I wonder if we are seeing long-branch attraction
>of (*B.* + *H.*). away from *G.*. The occurrence of MPTs where *G.* is outside
>(Hesperornithes + Neornithes) shows that the phylogenetic position of (*B.* +
>*H.*) is unstable.
I think I can interject here (from being on vacation)...
We simply used Clarke & Norell's matrix, with a few changes and additions
-- we didn't try to change or add codings from anything we hadn't personally
seen (well, Luis & Jingmai probably saw, and they did contribute to our changes
for a few things), including _Enaliornis_. This wasn't because we were/are
lazy -- we are trying hard to get the funding we'll need to go see as many of
these things in person as humanly possible -- but because our analysis was
preliminary. Like a lot of these kinds of phylogenetic analyses, we depended
on other people's codings to be accurate and simply added our stuff to get a
preliminary estimate of where _Gansus_ lay. We had kind of predicted it would
be fairly derived, based on its various characters, but were pretty surprised
that it came out as advanced as it did -- that was the thing that made it
_Science_-worthy. If/when we get our funding, we will do a much more detailed,
monographic osteology and comparison with lots of other things, and
hopefully all will made much clearer, including whether or not _Gansus_ really
is where we found it the first time (and yes, we have contemplated that it's a
basal hesperornithean, specifically one that was still volant). Rest assured
also that a brand-new data matrix is being compiled, based in part on Clarke &
Norell and others but with lots of new/changed characters and more accurate
codings.
We are aware of the various problems that convergence, long-branch
attraction, etc. can have on an analysis with a taxon like _Gansus_; we're
keeping all this in mind. Still, it does beggar the question of exactly how
much faith one can put in a computer-generated analysis when the human mind
says something else...are we Borg or are we capable of abstracting beyond a
bunch of statistics? (Not an argument I'm going to have here...)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT 84770 USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and dinogami@gmail.com
http://cactus.dixie.edu/jharris/
"Trying to estimate the divergence times
of fungal, algal or prokaryotic groups on
the basis of a partial reptilian fossil and
protein sequences from mice and
humans is like trying to decipher
Demotic Egyptian with the help of an
odometer and the Oxford English
Dictionary."
-- D. Graur & W. Martin
(_Trends in Genetics_
20[2], 2004)
- Follow-Ups:
- Re: *Gansus*
- From: David Marjanovic <david.marjanovic@gmx.at>