David Marjanovic 07 April 2002 wrote:
1) "Unnamed" is called "Amniotiformes" in http://dinosauricon.com/taxa /tetrapoda.html.
If it is probable that diadectomorphs are amniote, in my opinion, they should be placed within Amniota. "Amniotiformes" synonymous of "Amniotomorpha" is already used in Dinosauricon cladogram to name the clade that includes westlothiana. Why multiply names founded on soft tissue?
2) Sure it can. Pisces has been dismissed.
But not outside the door in the external world. Since science needs to be divulged after all. For example, the title of the beatiful book of John A.Long is "The rise of fishes" not "The rise of Craniates" as it would expected by orthodoxy for a book that start with myxinidae.
Inside you can find cladograms mixed with popular terms like: jawless fishes, ray finned fishes, etc.
T. Michael Keesey 08 April 2002 wrote:
1) This would suggest that epidermal scales are a reptilian synapomorphy, and that the mammalian lineage (synapsida)
never had them. Either the ancestral amniote had dermal scales, lost in both lineages, or it had smooth skin. The latter seems more likely to me.
Also today there are synapsids with epidermal scales, as has rat in the tail. The scales are the epidermal structure that is present in all the actual amniote lineages, although rare in mammals. As far as I know the alpha keratin (the only one in mammals) is also present in reptilian scales covered by beta keratin that is an advanced character of diapsids.
Ventral bony scales were found in pelycosaurs (Romer, Laurin & Reisz in Treeof Life). The retaining of this ancestral character demonstrates the need of belly protection in a sprawl pelycosaur. But it is unlikely that the dermal scales were present all over the body, because these heavy structures, in a terrestrial environmet, are destabilizing and
penalizing of the speed (Frolich), it is more probable, in my humble opinion, that the protection in the rest of the body of the first amniotes was assured by light alpha keratin scales, on which base, the diapsids joined the beta keratin.
It seems to me very improbable that, in a competition with keratin-scaly sauropsids, the synapsids substitute the dermal scales protection with a lissamphibian skin, considering also the fact that their actual descendants testify the capability of the synapsid skin to produce scales.
Actual lissamphibians evolved poison glands as an antidote to the loss of bony protection, but this seems not happened in early synapsids or, I think, we should see the survival of them in their descendants, but mammals with poison glands in the skin are extremely rare. Moreover lissamphibians being small, arboreal or fossorial, are more immune to predation;
it seems to me not realistic to imagine cotylorhyncus as a 350 Kgs. toad.
2) How can they diverge before sauropsids when they are the sister group to_Sauropsida_ ? By definition, both diverged from each other at the same time.
Perhaps is better, from my side, to say that synapsids are the earliest monophiletic lineage that can be well demonstrated to have diverged within amniota.