Re: Tiktaalik, Great Danes and speciation

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

> Is the example real plesiomorphy? I would rather call it plesiomorphy if E 
> and A were both the outgroups, i.e. E branching directly from a node with 
> A, and E not so close to D. But I may be wrong here.
>
> [...]
>
> I dare postulate, that (though not always perfectly, with possible 
> exceptions): for many clades the ability to interbreed is a synapomorphy 
> and a monophyletic shared trait,

Sure it's a shared trait -- but a _retained_ one. Either you can interbreed, 
or you can't interbreed _anymore_.

> (the degree of) which is a good reflection of taxonomic/evolutionary 
> relationship, and can as such be used to distinguish clades. Or in other 
> words: ability to interbreed will never be a result of convergence.

Above, however, you _are_ postulating that the ability of A and E to 
interbreed is the result of homoplasy.

> Reasoning in this way, the ability to interbreed, either fertile or 
> sterile, would be the node for a clade, corresponding to the biological 
> genus level; the ability to interbreed fertile would be the node for a 
> clade nested within it, corresponding to the biological species level.

Then what do you do with examples where it only works if one species is the 
father and the other the mother, but not the other way around?

> Phylogenetics based on interbreeding

What do you mean?