[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: If Dinosaurs Could Fly




On Mon, 19 Jan 1998, Matthew Troutman wrote:

> >
> >This is not to say, though, that contour feathers can have no 
> insulating
> >function.  More to the point, it says nothing about the insulating
> >properties of "protofeathers", if that is what the structures on
> >Sinosauropteryx really are.  And it avoids other possible uses of body
> >feathers such as display.
> 
>       The only true insulatory feathers are the degenerate ( lacking 
> derived barblets) of ratites and flightless birds. Down is not an 
> effective insulator in wet conditions. One of the main causes of infant 
> mortality in juvenile birds is when the down feathers get wet and they 
> die of hypothermia. Pretty maladaptive.

DOwn is not entirely maladaptive. It does have its points, one of which is
to trap heat and baffle wind away from the skin. Juveniles that go through
a down phase do so when they are confined(either by lack of motive ability
and general helplessness or by parents) to the nesting area and therefore
more likely to be protected from the elements. The transition from
nest-bound chick to mobile juvenile is a dangerous time anyways and dying
from hypothermia is probably about as likely as being snagged by a
predator or breaking your neck learning to fly.  

 > 
> >>  The
> >>feathers from which down feathers are derived functioned in flight, 
> not
> >>insulation. 
> >
> >There is simply no hard evidence of which I am aware to support this
> >statement.  Frankly, we do not know whether contour and down feathers 
> (as
> >well as bristles, filoplumes and other feather types) evolved from 
> flight
> >feathers, or all of these evolved from an ancestral type (which might 
> have
> >been the Sinosauropteryx-type protofeather).  
> 
>      Down feathers and filoplumes can be traced to contour feathers 
> quite easily. And as stated above down as insulation is maladaptive


Perhap as an overall lifespan strategie of insulation yes, buI wouldn't be
so general. If it were a complete and utter failure then it wouldn't show
up at all having  been selected against. 

>      I agree here. There must be in essence a " pre-contour/flight 
> feather".

Me too....


---Steve