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Re: Morpho v molecular (was Re: Tinamous: living dinosaurs)
Mickey Mortimer <email@example.com> wrote:
> I don't know enough about mammals to have an informed opinion, of course.
> But Uhen's review you mention accepts Whippomorpha as the most likely
> hypothesis, and he is a paleontologist. Note too
> the support of Whippomorpha from O'Leary, Spaulding, Geisler, Theodor,
> Boisserie and other paleontologists. The most recent and largest
> morphological analysis I know is Spaulding et al. (2010),
> with 661 phenotypic characters (and 46587 molecular ones) and 81 taxa.
Yes, but as you say, this study relies upon total evidence (morphology
+ molecules). As Spaulding &c themselves put it: "Trees based only on
data that fossilize continue to show the classic arrangement of
relationships within Artiodactyla with Cetacea grouping outside the
clade, a signal incongruent with the molecular data that dominate the
total evidence result." And among the other morphology-based studies
mentioned by you are phylogenies that are at odds with both the
"classical" topology (Artiodactyla and Cetacea as sister taxa) and the
topology given by molecular-based phylogenies (Whippomorpha as the
sister taxon to ruminants).
So the Whippomorpha issue is 'messy' to say the least. The topology
of Cetartiodactyla as given by molecular-based methods has varying
support from fossil/morphological studies. Paleontologists who find
support for some kind of hippo-whale clade (Cetancodonta/Whippomorpha)
do not necessarily agree on the content and relative position of this
> Turtle relationships are still equivocal given the current analyses- just a
> year earlier, two of the Lyson et al. coauthors wrote a paper suggesting
> evidence for archosauromorph turtles. Just because the
> latest paper supported parareptile turtles doesn't make it the morphological
Yes, I'm not claiming that the "turtles-are-parareptiles" hypothesis
is the final word, or even represents the morphological consensus. I
was just using this as an example of a morphological v molecular
conflict. What I'm driving at here is that the molecular support for
a "turtles-are-archosauromorphs" hypothesis is not backed up by
morphological/fossil evidence. If the problem is that inadequate
taxon sampling is generating a spurious phylogenetic signal, then this
is a problem that can be potentially redressed by future fossil
discoveries. On the other hand, I don't think we can assume that
piling up ever-larger multigene datasets drawn from the restricted
pool of extant taxa is going to lead us to the "right" answer.
> But at least with molecular data we don't have to worry about human bias in
> choosing characters, small numbers of characters, or miscoding (I'm sure any
> sequencing errors are much less frequent than
> what is common in morph data matrices at least).
For molecular-based phylogenetic analyses, there are much bigger
problems than mere sequencing errors.