Re: Dino down

["Matthew Troutman" <m_troutman@hotmail.com>]

<<Well, young penguins (to my inexperienced eye) appear to have down 
only, but of course live in a dry climate. What if, down was developed 
in dinosaurs as a juvenile characterisitc only, to provide them with 
additional thermal protection while in the nest until such time as 
activity and body mass passed to a level where body temperature became 
self-sustaining?>>

Young penguins are also shielded from the weather by their parents.  
Down could have evolved as a juvenile characteristic but not before any 
other type of feathers.  

<< (it has always puzzled me that if the reason often given to explain 
the absence  of  small dinosaurs is one of a mass/surface area 
temperature control; yet we have dinsoaurs hatching from eggs and being 
below the "critical size" without any explanation of how they stayed 
"warm". Hmm they could have had a higher metabolic rate than adults but 
I like the idea of downy baby dinos ! <aaaahh!>)>>

Greg Paul (1994) has shown that baby dinosaurs probably did have down 
feathers, but this was based primarily on the assumption that dinosaurs 
were endothermic at least when the animal was a juvenile.  Though I do 
believe that dinosaurs were probably ectothermic, a downy layer of 
feathers was possible in juveniles.  However, it should be noted that 
dinosaurs did have open nests where the juveniles (with their presumed 
downy pelage) would be exposed to wet weather which would drive them to 
hypothermia when the feathers would get wet.  Regardless of whether or 
not juvenile dinosaurs did have down insulation, the parents would still 
have to sheild the babies.  

I should note, however, that if hadrosaurs and their kin were altricial, 
then it is unlikely that they would have down feathers.  Altricial 
animals are born naked and poikilothermic and grow rapidly.  Since 
hadrosaurs were at the size (and not to mention phylogenetic position) 
where feathers were unlikely, then it is unlikely that feathers were 
present in the young. If hadrosaurs were semi-altricial then feathers 
would be more likely.  We should be looking at precocial dinosaurs like 
the theropods for downy juveniles.  

Matt Troutman

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