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Re: was Lu and Ji 2006/paedomorphic salamanders
----- Original Message -----
From: "David Peters" <firstname.lastname@example.org>
Sent: Friday, June 09, 2006 12:47 PM
While every study sheds light on the sticky subject of evolution,
think about what salamanders do when they go paedomorphic.
They become little rhipidistians or basal tetrapods (really the same
thing, right?), without the scales. That's about as basic and
pleisomorphic as you can go. No wonder they all converge!
What makes you think they should go all the way to the origin of an
apomorphy-based Tetrapoda, or, more importantly, to any _specific_ point?
No, no. They lose apomorphies all across the board. They retain some -- not
all -- lissamphibian, batrachian, caudate, and urodele characters. _Have you
read the paper?_ They tend to cluster with each other and with the caudate
Whether you want to call tiny pterosaurs tiny adults or tiny babies,
it doesn't matter to me what your religion is. The fact of the matter
is, when tiny pteros are included in a matrix relationships between
sister taxa become clarified, changes between sister taxa take on a
spectral blend and you get a single tree with crazy derived forms at
the tips of bushy branches and the metaphorical 'plain brown
sparrows' forming the backbone of the chain.
But, you see, this is _*NOT*_ an advantage for you. It would only be if the
pterosaur fossil record were _almost complete_, which is the opposite of
reality. We have _zero_ reasons to expect that our tiny sample of pterosaur
diversity should show "a spectral blend".
(While I am at it, don't trust Cope's rule of the unspecialized too much.
Alligators are secondary generalists derived from durophages with
durophagous dentition; tetrapods as a whole are descended from top predators
specialized for lurking in shallow, vegetation-choked water; *Dakosaurus*
had specialized predators on small fish among its ancestors... In other
words, it certainly doesn't hurt if the reconstructed ancestors in your
cladogram are all "plain brown sparrows", but this is _entirely_ negative
Sharp beaks go with sharp beaks. Horizontal
teeth go with horizontal teeth. Small pectoral
complexes go with... well, you get the picture.
That's inevitable in a cladogram anyway. :-| (Unless you are only talking
about the characters you happen to find most conspicuous or most
interesting -- differences that cladistics doesn't make.)
Surprising what can happen when you just let it happen without a
Sure, but some a priori assumptions are there for a _good_ reason.