From
Wikipedia,
the free
encyclopedia.
A
feather
is one of
the
epidermal
growths that
forms the
distinctive
outer
covering, or
plumage, on
a
bird.
They are the
outstanding
characteristic
that
distinguishes
the Class
Aves
from all
other living
groups.
Other
Theropoda
also had
feathers
(see
Feathered
dinosaurs).
Characteristics
Feathers
are the most
complicated
integumentary
structure
among the
vertebrates.
Like hair,
nails and
scales,
feathers are
integumentary
appendages;
skin organs
that form by
controlled
proliferation
of
cells in
the
epidermis,
or outer
skin layer,
that produce
keratin
proteins.
They
insulate
birds from
water and
cold
temperatures
and provide
colour which
is sometimes
used as
camouflage
against
predators
and
sometimes as
a means of
visual
communication.
Although
individual
feathers are
very light,
a bird's
plumage
weighs two
or three
times more
than its
skeleton.
There are
two basic
types of
feather:
vaned
feathers
which cover
the exterior
of the body,
and down
feathers
which are
underneath
the vaned
feathers,
providing an
insulating
layer. The
pennaceous
feathers
are vaned
feathers.
Also called
contour
feathers,
pennaceous
feathers are
distributed
over the
whole body.
Some of them
are modified
into
remiges,
the flight
feathers of
the wing,
and
rectrices,
the
flight
feathers
of
the
tail.
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Close-up
of a
single
white
feature
(click
to
enlarge) |
A
typical vaned
feather
features a
main shaft,
called the
rachis.
Fused to the
rachis are a
series of
branches, or
barbs; the
barbs
themselves
are also
branched and
form the
barbules.
These
barbules
have minute
hooks called
barbicels
for
cross-attachment.
Down
feathers are
fluffy
because they
lack
barbicels,
so the
barbules
float free
of each
other. At
the base of
the feather,
the rachis
expands to
form the
hollow
tubular
calamus,
or quill,
which
inserts into
a
follicle
in the
skin.
parts of a contour feather
A bird's
feathers are
replaced
periodically
during its
life through
molting,
new feathers
are formed
through the
same
follicle
from which
the old ones
were
fledged.
Some
birds have a
supply of
powder down.
Powder down
feathers
grow
continuously,
with small
particles
regularly
breaking off
from the
ends of the
barbules.
These
particles
produce a
powder
that sifts
through the
feathers on
the bird's
body and
acts as a
waterproofing
agent and a
feather
conditioner.
Most
waterbirds
produce a
large amount
of powder
down.
Bristles
are stiff,
tapering
feathers
with a large
rachis but
few barbs.
Rictal
bristles
are bristles
found around
the eyes and
bill. They
serve a
similar
purpose to
eyelashes
and
vibrissae
in
mammals.
Origins
Feathers
most likely
originated
as a
filamentous
insulation
structure,
or possibly
as markers
for mating,
with flight
emerging
only as a
secondary
purpose. It
had been
thought that
feathers
evolved from
the
scales
of
reptiles,
but recent
research
casts doubt
on this
homology
(see
Quarterly
Review of
Biology
77:3
(September
2002):
261-95).
Experiments
show that
the same
protein
(when
missing
before
birth) that
causes bird
feet to stay
webbed,
causes
reptile
scales to
become
feathers. [[1]
Feathered
dinosaurs
Main
article:
Feathered
dinosaurs
Although
birds use
feathers
primarily
for flight,
several
dinosaurs
have been
discovered
with
feathers on
their limbs
that would
not have
functioned
for flight.
One theory
is that
feathers
originally
developed on
dinosaurs as
a means of
insulation;
those small
dinosaurs
that then
grew longer
feathers may
have found
them helpful
in gliding,
which would
have begun
the
evolutionary
process that
resulted in
some
proto-birds
like
Archaeopteryx
and
Microraptor
zhaoianus.
Other
dinosaurs
discovered
with
feathers
include
Pedopenna
daohugouensis,
Sinosauropteryx,
and
Dilong
paradoxus.
Currently
the question
is whether
birds are
deinonychosaurians
or
dromaeosaurids,
not whether
birds are
dinosaurs.
It has been
suggested
that
Pedopenna
is older
than
Archaeopteryx,
however,
their age
remains
doubted by
some
experts.
Dilong
is a
tyrannosauroid
which
predates
Tyrannosaurus
rex
by 60 to 70
million
years.
Human
uses
Feathers
are both
soft and
excellent at
trapping
heat;
thus, they
are
sometimes
used in
high-class
bedding,
especially
pillows,
blankets,
and
mattresses.
They are
also used as
filling for
winter
clothing,
such as
coats.
They have
also been
put to use
as
sexual aids;
see
feather
dancing.
Colorful
feathers
such as
those
belonging to
pheasants
have been
used in the
past to
decorate
hats and
fishing
lures.
In
Greek
mythology,
Icarus
tried to
escape his
prison by
attaching
feathered
wings to his
shoulders.
Feathers can
also be used
to
tickle
people.
Categories:
Feathers
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