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Re: AW: Heterodontosaurid with protofeathers



Quoting Dora Smith <villandra@austin.rr.com>:

> Hair is such a good idea that something like it evolved at least 
> twice; in mammals and in therapod dinosaurs (maybe all dinosaurs, maybe 
> not). 

'Hair' is a fairly specific term that really only refers to mammalian 
integumentary structures.

If you mean integumentary structures in general, then they could have evolved 
at least three 
times, depending on whether or not dinosaurs and pterosaurs had a fuzzy common 
ancestor.  
Possibly more than three. There's no reason to assume that fur evolved just 
once amongst 
mammals, let alone amongst dinosaurs.

> It would have been in response to - the weather.

It's clearly not that simple, since plenty of non-fuzzy animals are also 
exposed to the weather. 
Insulatory integumentary structures are only useful in endothermic animals, 
since they're 
downright maladaptive in ectothermic beasties. 

In fact it could be argued that insulation is *mandatory* if you're 
endothermic, experiencing 
temperature fluctuations on a regular basis (the 'naked mole-rat clause'), and 
are below a certain 
size threshold (the threshold itself being determined by the extremity of the 
temperatures 
endured). I'd be surprised if *any* small non-burrowing or non-aquatic 
endotherms at any time in 
the past didn't have some sort of insulatory integument.

-- 
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Dann Pigdon
GIS / Archaeologist              http://geo_cities.com/dannsdinosaurs
Melbourne, Australia             http://heretichides.soffiles.com
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