feathers as N2 excretors

[Martin Human <cockatoo@csi.com>]

Further to the suggestion that feathers are actually a pathway for the 
excretion of Nitrogen products, does this imply that fur, hair, nails, 
scales etc are for the same purpose? Was this considered by the proponents 
of this idea, anyone?

Should we then consider that all manifestations of specialisation may be 
mere secondary adaptations of the need to eliminate waste products, so that 
shells on eggs are a means of ridding the body of excess calcium or other 
chemicals, as are losing milk teeth, leaving your teeth in carcasses, 
developing pupae cases, spinning webs, producing slime, growing shells, to 
name but a few potential candidates?

But then I have to remember that arsenic, if ingested,  can be found in 
hair and nails. Hmmm.

martin