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Theropod phylogenies



>>Tim Williams said
>>The biggest obstacle to resolving the interrelationships
of modern birds is their fossil record: It's utterly dreadful.<<

I don't understand: if we can't resolve the relationships of modern birds,
how does fossil evidence help?

>>Darren Naish said
>> Richard, while cladistics consistently
supports the nesting of birds within Theropoda, even if you
are a vehement frothing-at-the-mouth never-to-be-converted
angry ANTI-cladist, simple morphological comparison will
convince you that birds are theropods. Indeed, note that
many who support the theropod nature of birds are highly
critical of cladistics (e.g., Bakker, Frey). There is no
theropod/bird boundary - the two grade into one another via
a multitude of intermediaries - and the two share
innumerable detailed characters of all parts of the skeleton
and soft tissue. Those few who argue that birds cannot be
theropods consistency avoid/are unaware of/ignore this
huge body of morphological evidence. <<


I'm not arguing against nesting (!) of birds within theropoda - the evidence
seems overwhelming. It seem to me, as a non-theropod worker (I think there
are more interesting extinct animals than big dead chickens) that the
interesting question to be addressed is 'do all modern birds form a single
clade within the theropoda?
My point was more to do with the way in which cladistic analyses is used to
construct diagrams of relationships which are then treated as phylogenies.
Indeed, the PhyloCode seems to be devised to set such pseudo-phylogenies in
stone.

>>themage@thedigs.dnsalias.net
>>You may never be able to falsify many particular stories of mutation
and selection, but surely with independent molecular data, the idea of
the applicability of parsimony itself is available to a much higher
standard. How much closer to the results of molecular biology than the
best of traditional methods will the most parsimonious cladograms take
you?<<
>>Thomas R. Holtz
>>Well, to be fair, DNA analyses will often give wildly different topologies
depending on the particular genes and the particular subset of taxa
used...<<

It would be naive to assume that any particular character set -
morphological, molecular, or DNA - is better than any other until we have a
far greater understanding of the genetic mechanisms which give rise to those
character. The danger is always that the newer method is seen as more
acurate - until we realise that convergence occurs not just gross
morphology, but also in biochemistry and elsewhere. Perhaps a productive
approach would be to compare cladistic analyses using different data sources
in modern birds - morphological, protein data, DNA - and find the characters
within the different sets which converge. If we have a reduced morphological
character set for modern birds, but one which we know produces a similar
diagram of relationships to molecular and DNA analyses, we would have some
justification for infering that a morphological analysis on (?other)
theropods using the same character set is likely to lie closer to a 'true'
phylogeny than one produced by using anything anyone has ever described as a
character.

Richard Forrest
richard@plesiosaur.com
www.plesiosaur.com

"Minds are like parachutes: they only function when they are open"
James Dewar