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Re: Tree of Life webpage
As a follow up to the questions I had on the TOL webpage, I must ask
about the phylogeny they present for the stem tetrapods...
Incidentally, be aware that although it says "Michel Laurin" on the
label, the position of *Whatcheeria* is based on another (and, frankly,
way outdated) phylogenetic hypothesis. Maybe Jennifer Clack inserted it.
For crying out loud, all three sufficiently well preserved whatcheeriids
are known to retain the preopercular bone!
The TOL presents Temnospondyls as diverging before the
Amniote-Amphibian split, which would seem to suggest they weren't
amphibians at all, but rather some sister taxa to Amphibians&[Amniotes]
Yes. This is the "lepospondyl hypothesis" on the origin of
Lissamphibia*, found by Michel in a series of papers ending in Vallin &
Laurin (2004) starting with his PhD thesis in 1994 (on seymouriamorphs);
also found by the PhD thesis of Kat Pawley (2006 -- you can download all
the interesting chapters here
by the PhD thesis of Damien Germain (2008 -- supervised by Michel, but
done very independently), and by... Marjanovic & Laurin (2008, 2009).
* That's the crown-group: frogs, salamanders, caecilians, and maybe
Whereas wikipedia's Temnospondyl page seems to firmly place them
within Amphibia (ie after the amniotes split from the linage that
gave rise to modern amphibians), and suggests lissamphibians may even
be a branch of the temnospondyl tree (rather than a side-branch like
Yes. This is the "temnospondyl hypothesis" on the origin of
Lissamphibia. The latest paper that found it is Ruta & Coates (2007).
Because that analysis is based on a big matrix, and for historical
reasons, this hypothesis is currently the most widespread one among
people who work on Paleozoic limbed vertebrates.
Meanwhile the Labyrinthodontia page presents a phylogeny
Why does it present a phylogeny? With one exception in 1985, nobody ever
seems to have believed it ( = big non-amniote limbed vertebrates) was a
clade, and the term has hardly been used for the last 20 years.
that seems to confirm the TOL phylogeny (as far as the Temnospondyls go,
but not as far as Westlothiana and Seymouriamorphs) despite naming stem
tetrapods as amphibians.
Westlothiana is pretty clearly the basalmost known amphibian, or anyway
Wikipedia also presents seymouria and westlothania as closer to
amniotes than amphibians, whereas TOL presents them as basal to both.
So what are the views of people on this list. Did the following
emerge before or after the modern amphibians and modern amniote
And I haven't even mentioned the "polyphyly hypothesis" yet.
Its normal version (Anderson et al. 2008; also supported by Carroll up
to 2007 [and I think his new book], even though the results of his
phylogenetic analysis in 2007 say something different) has the frogs and
salamanders sitting in the temnospondyls, just like in the temnospondyl
hypothesis (except for the version where the frogs are amphibamids and
the salamanders are branchiosaurids, but this has _never_ been found by
a phylogenetic analysis), but the caecilians among the "microsaurian"
lepospondyls. Then there's a weirdo version (McGowan 2002; results of
Carroll 2007), where again the caecilians are "microsaurs"... and the
"microsaurs" and all other lepospondyls sit _inside the temnospondyls_.
We (2008) showed that the results McGowan (2002) found were due to the
mistakes in his data matrix. We (2009: supp. inf.) further showed that
the results Anderson et al. (2008) found were due to the mistakes in
their data matrix. Both matrices actually support the lepospondyl
Damien Germain (thesis 2008) showed that correcting hundreds of mistakes
in the matrix by Ruta & Coates (2007) leads to the lepospondyl
hypothesis being found as one step more parsimonious than the
temnospondyl hypothesis. Because he didn't have time to go on (French
theses are time-limited, and Damien had no financing...), I am
continuing this work right now. As of today, Mesquite claimed the
lepospondyl hypothesis to be seven steps more parsimonious; PAUP* is now
See you in Bristol next week!
PS: It goes without saying that I don't imagine the current broadside to
be the last word. Seven steps out of 1808 is not a lot. The matrix by
Ruta & Coates (2007), the largest properly published one (Pawley made
several larger ones), has 102 taxa and 339 characters, of which 335 are
parsimony-informative; I merged lots of correlated characters, so only
300 characters are left, which is less than three times the number of
taxa. Indeed, I can easily think of several characters that are
potentially interesting to not just limbed-vertebrate phylogeny in
general, but the question of lissamphibian origins in particular, and
that are missing from that matrix. Furthermore, the matrices of Vallin &
Laurin (2004), Anderson et al. (2008)/Marjanovic & Laurin (2009), and
Ruta & Coates (2007)/Marjanovic, Germain & Laurin (in prep.) each
contain both taxa and characters that are missing from both others...
and there's no chroniosuchian in any of them... We are living in
Too bad my abstract was only accepted as a poster presentation.
Saturday, September 26th.
PPS: The bootstrap tree of Laurin & Reisz (1999) is right: the
temnospondyls are more closely related to us than the
anthracosaurs/embolomeres are, not vice versa.