Re: Scales, hair, integumentary structure relationships?

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

> So what of the dermal scales, if some caecilians have dermal scales, does 
> this imply the trait was lost after the amphibian amniote split?

Pretty certainly.

> Or is it more likely the caecilians re-evolved/reverted to dermal scales 
> (atavism) - which isn't too unlikely.

I completely forgot to mention that the albanerpetontids, known from the 
Middle Jurassic to the late Pliocene and probably the sister-group of 
Lissamphibia, had well-ossified scales all over their bodies.

Also, the caecilians are the sister-group of the frogs plus salamanders. So 
it seems that the loss only happened during the origin of the 
frog-salamander clade.

> A few years back they found a mutant chicken with teeth in its beak -

Really? Can you give us a source for that?

> the dermal scales could have been absent in the common ancestor of 
> amniotes and amphibians, and the genes for dermal scales later 
> re-activated in the caecilian lineage?

Unlikely, see above.

> Some birds (hoatzin, african touraco, the ostrich?) seem to have 
> re-evolved claws, using the genes already present in their genome

No, most extant birds have small claws on one or two fingers per wing. Check 
out the next chicken or turkey on your table!

> Its kind of funny to imagine the confusion that would happen if 50 million 
> years from now, the only chicken fossils known (to whatever palentologists 
> are still here, of whatever species) had teeth and claws- wouldn't that 
> make placing them on a tree hard?(would they try to group it with more 
> primitive toothed birds?)

That would just be two characters out of several hundred (assuming today's 
methods of phylogenetics). It would hardly matter.