pterylae

[brushes2@juno.com]

Discussion of the arrangement of feathers in tract, the pterylae, has
brought up some interesting comments. The tracts generally refer to
contour (vaned) feathers. These are the feathers that define the body
shape and contain the flight feathers. Other types of feathers also occur
in the pterylae. The apteria, the spaces between the pterylae, may
contain a variety or feathers such as down, filoplumes,etc. Or they may
be naked. We have a pretty good idea of the chemical messages that
determine the distribution of the feather follicles that form the
pterylae. They are different from those area that form scales. If the
messages are disrupted a slatelike structure may form, but it is NOT a
'true' scale. So the distribution of scales in some ancestor is not
likely to determine the nature of the pterylae in some decedent. They are
different things.

One interest item is that there have been no explanations of the possible
adaptive signifince of having the contour feathers in tract (as opposed
to having them uniformly distributed over the animals body. There is, of
course, functional signifince to bare body parts (eg the face and head of
vultures, etc).  It has been demonstrated that a bird whose feathers have
been removed is incapable of compensating for the heat loss. Even though
the metabolic rate is elevated close to its maximum, the loss of the
insulation overwhelms the capacity of the system and the body temperature
falls.

The patterns of the scales on reptiles had not been studies as
extensively.

Cheers,

Alan