Re: synapsids are reptiles

["T. Michael Keesey" <mightyodinn@yahoo.com>]

--- Jura <archosaur@reptilis.net> wrote:
> 
> Amphibian scales are roughly the same as those in fish (i.e. dermal in nature 
> and not made from
> keratin ;IIRC). As I've stated before, reptile scales are a form of 
> integument. They are
> epidermal in nature and there is skin between them. 
> 
> I'm not sure how unique (apomorphic) these scales are to reptilia itself 
> though. I also don't
> know why synapsids are now considered to be scaleless. 
> 
> Do we have any actual evidence to support scalelessness, or is this based off 
> of cladistic
> positioning (in which case, I still don't see why they would be considered 
> scaleless)?

It seems to make sense to me:

--+--Actinopterygii (dermal scales)
  `--+--Coelacanthormpha (dermal scales)
     `--+--Dipnoi (dermal scales)
        `--+--+--Gymnophiona (dermal scales)
           |  `--+--Urodela (smooth skin) 
           |     `--Salientia (smooth skin)
           `--+--Reptilia (epidermal scales)
              `--Mammalia (hair)

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.

Now, this could be shown wrong if a synapsid were shown to have epidermal 
scales homologous to
those of reptilians.


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=====> T. Michael Keesey <keesey@bigfoot.com>
=====> The Dinosauricon <http://dinosauricon.com>
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