Re: was Lu and Ji 2006/paedomorphic salamanders

[David Marjanovic <david.marjanovic@gmx.at>]

----- Original Message -----
From: "David Peters" <davidrpeters@earthlink.net>
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 
stem.

> 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 
evidence.)

> 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
> priori assumptions.

Sure, but some a priori assumptions are there for a _good_ reason.