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Re: Synapsids weren't reptiles? I'm confused.



I looked at the archives on this mailing list, and of the papers mentioned, it 
seems the only conclusion that can be positively made, is the keratin in 
pangolins is dissimilar from typical mammalian alpha keratin, and keratin found 
in bird feathers.
The paper only looked at amino acid profile, and it matched neither hair nor 
feather.

Is it a mixture of 2 different keratins? or 1 type of keratin with intermediate 
properties?

Even if it has beta-structure, its not neccesarily beta-keratin - if beta 
keratin refers to a specific amino acid sequence (phi-keratin has beta 
struture, but is commonly not refered to as beta keratin).

Likewise, I doubt any keratin with beta structure in Pangolins has much 
sequence homology with "reptile beta-keratin" (beyond the homology between 
common alpha and beta keratins)

Either way, I think the extant amniote species can be assigned to the synapsids 
or diapsids based on keratin structure. All living reptiles clearly have 
keratin distinct from that found in mammals - even if some mammals have keratin 
distinct from other mammals, it is still distinct from reptillian/sauropsid 
keratin.

--- On Wed, 7/2/08, Dann Pigdon <dannj@alphalink.com.au> wrote:

> From: Dann Pigdon <dannj@alphalink.com.au>
> Subject: Re: Synapsids weren't reptiles? I'm confused.
> To: dinosaur@usc.edu
> Date: Wednesday, July 2, 2008, 8:01 PM
> Erik Boehm writes: 
> 
> > Only reptiles have beta keratin - and scales
> ("reptile type" scales, not the "fish
> type"), don't know when these evolved, but they
> are currently diagnostic for synapsids vs sauropsids, and
> ancestral to the crown group.
> 
> Pangolin scales have a mixture of alpha and beta keratins. 
> 
> Alpha keratin tends to have a specific elongation of around
> 100% (elasticity 
> and plasticity), while beta keratin is closer to 0%.
> Pangolin scales have a 
> specific elongation of around 15%, so they're actually
> closer to reptile 
> scales in that respect. 
> 
> ___________________________________________________________________
> 
> 
> Dann Pigdon
> GIS / Archaeologist             
> http://geo_cities.com/dannsdinosaurs
> Melbourne, Australia            
> http://heretichides.soffiles.com
> ___________________________________________________________________