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Re: ASSORTED SUBJECTS



Subject: ASSORTED SUBJECTS 
Author:  <m_troutman@hotmail.com> at SMTP
Date:    6/10/98 3:23 PM
     
FEATHERS AND PHYSIOLOGY
     
An animal that has feathers does not necessarily be endothermic.  
Woodhoopoes (and all Coraciiformes) do not have great temperature 
control even though they have feathers.  Though they are endothermic 
tachymetabolic homeotherms during most of the day, they are not so much 
during nights, where they need to seek refuge in a tree trunk to 
withstand hypothermia.  Feathers, especially downy feathers, can provide 
good insulation, but this would be advantageous to both endotherms and 
ectotherms.  
     
     {Woodhoopoes are perfectly good endothermic homeotherms, they simply 
     practice a slightly exagerrated version of the shallow nocturnal 
     hypothermia seen in most small birds, presumably as an 
     energy-conserving strategy not quite as extreme as true torpor.
        And insulation per se is not of any use to a true ectotherm 
     _unless_ (hypothetically, because no extant etotherms do this) it can 
     be "turned off and on", that is, if it could be bypassed completely to 
     allow heat gain from the environment and in other circumstances 
     activated to retard heat loss. Downy feathers seem to me the least 
     likely form of known insulation to be able to accomplish this. In 
     fact, although I am extremely sceptical about endothermic homeothermy 
     in dinosaurs (extremely!), I'd actually buy it if you could show me a 
     downy dinosaur fossil (what I know of Sinosauropteryx is not - yet - 
     compelling enough for what I still regard as an extraordinary claim).}