Page 90 - The Origin of Birds and Flight

88 The Origin of Birds and Flight

At the morphological level, feathers are traditionally considered
homologous with reptilian scales. However, in development, morpho-
genesis, gene structure, protein shape and sequence, and filament for-
mation and structure, feathers are different. 61
An interview by Dr. Carl Wieland with Dr. David Menton of the
Washington University Medical Faculty covered the impossibility of rep-
tile scales evolving into bird feathers:
Dr. Carl Wieland: . . . Of course, evolutionists have long argued that
feathers evolved from reptile scales and are thus fundamentally the
same structure—very similar.

Y
R
D
F
F
I

V
E
A
I
N

E
C
A
S
N

L
D
O

E
S
A
T

N
R
E
W
T
H

A
Y
F FEATHERS GROW IN A VERY DIFFERENT WAY THAN SCALES DO
E
E
T
A
H
R
R
O
W
S

G
(3)
Feathers do not differ from The would-be feather
scales only in terms of structure,
but also in the way they develop.
Feathers grow by keratosinites
The would-be feather
(cells that form keratin) increas- (2)
ing and diverging from one
another. When these keratin-pro-
ducing cells in the epidermis
(outer skin) layer die, they leave
behind an accumulation of kera- Cell Follicle (small sac)
densification Plaque (placode)
tins—strong but flexible protein Inner skin
(1) Epidermis of the sac
fibers. Feathers develop from (outer skin)
beta-keratins. The sheath out-
side a growing feather is made
Dermis (lower skin)
out of softer alpha-keratin.
Outer sac skin
Feathers arise from cavities
(1) Feather growth begins with the thickening – with a pla-
under the skin known as papillae
code – of the epidermis and concentration of cells in the
and cover almost a bird’s entire
dermis.
body.
(2) This placode later forms an extended tube known as the
Each cavity is supplied with a
feather seed.
large quantity of blood capilla-
(3) The cells that multiply in ring form around the would-be
ries to ensure feather growth.
feather form the follicle that makes the feather. The con-
Feathers, with their strong but
stant manufacture of keratinosites in this ring at the base
light structure, are different from
of the follicle propels old cells upward and outward, and as
scales and all varieties of skin,
a result, the feather initially emerges in the form of a tube.
thick or thin, hirsute or not.