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Re: Senter 2004 - Renesto and Binelli 2005 (long)

On Jun 24, 2007, at 4:12 AM, Christopher Taylor wrote:


< l.p.h.: highly derived taxa so low on the tree?

      |  |--Longisquama
      |  `--Megalancosaurus
< Logic problem here: L. and M. are nested within rib gliders? Again,
no common skull, manus, pedes, pelvic or pectoral patterns can be
seen here.

      `--[other diapsids]

Taking this tree as accurate and accepting _Coelurosauravus_ as a
rib-glider for the sake of argument, _Longisquama_ and _Megalancosaurus_
are not nested within rib gliders in it unless all other diapsids are as
well. It would seem much more likely to interpret rib-gliding as
homoplasious between _Coelurosauravus_ and _Icarosaurus_ than to
interpret rib-gliding as ancestral for the clade of most diapsids and
subsequently lost in the vast majority.

Only branching order is informative in a cladogram, not necessarily the
order taxa are in from top to bottom. Remember, the tree above is
exactly the same as

|  |--Megalancosaurus
|  `--Coelurosauravus
`--+--[other diapsids]

or any other permutation of order you might think of that still retains
the same branching.


Paliguana and Saurosternon make better basal sister taxa to Coelurosauravus, which becomes basal to the other rib gliders-- and that's where it ends -- as it should.

P. and S. also make for parsimonious sister taxa to Homoeosaurus and the rest of the lepidosaurs up through snakes, megalancosaurs, longisquamids and pterosaurs.

It should raise red flags for you when such specialized and highly derived forms (rib gliders, tail hookers, plume raisers) are nested (1) so close together without any demonstrated morphological similarities and (2) without any linking taxa and (3) so close to the base of a much larger and less well-endowed clade. You're putting the Styracosaurus before the Psittacosaurus. Linking taxa are known. No one wants to talk about the brown sparrows. Everyone wants to talk about the flashy peacocks and quetzals.

Both Megalancosaurus and Longisquama show far too many derived characters to ever be considered basal in any sort of logic. Think how difficult it would be to nest only bats, dolphins, cows and monkeys without having some sort of understanding of little furballs from the Mesozoic. Those intervening taxa are known and should be shown.

More taxa create more resolution. Less 'by default' nesting'

And the Senter nesting, sparse as it is, unfortunately also comes to us via lots of mistaken and missing characters.

Thanks for the comment.



        Christopher Taylor

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