From Wikipedia,
the free encyclopedia.
In
biology, dactyly is the
arrangement of
digits (fingers
and
toes) on the
hands,
feet, or sometimes
wings of an
animal. It comes from the
Greek word δακτυλος, meaning
"finger".
Sometimes the ending "-dactylia"
is used. The adjectival forms end
with "-dactyl" or "-dactylous".
By number
Pentadactyly is the
condition of having five digits on
each limb. All land vertebrates
are descended from an ancestor
with a pentadactyl limb, although
many groups of species have lost
or transformed some or all of
their digits.
Tetradactyly is the
condition of having four digits on
a limb, as in
amphibians and many
birds
Tridactyly is the
condition of having three digits
on a limb, as in some
birds and ancestors of the
horse such as
Protohippus and
Hipparion.
Bidactyly or
didactyly is the condition of
having two digits on each limb, as
in the
Two-toed Sloth, Choloepus
didactylus. In humans this
name is used for an abnormality in
which the middle digits are
missing, leaving only the thumb
and fifth finger.
Monodactyly is the
condition of having a single digit
on a limb, as in modern
horses.
Syndactyly is a
condition where two or more digits
are fused together. It occurs
normally in some
mammals, such as the
siamang. It occurs as a rare
abnormality in humans.
In birds
Anisodactyly is the most
common arrangement of digits in
birds, with three toes forward and
one back. This is common in
songbirds and other
perching birds, as well as
hunting birds like
eagles,
hawks, and
falcons.
Syndactyly in birds is
like anisodactyly, except that the
third and fourth toes (the outer
and middle forward-pointing toes)
are fused together, as in the
Belted Kingfisher, Ceryle
alcyon.
Zygodactyly (from Greek
ζυγον, a
yoke) is an arrangement of
digits in birds, with two toes
facing forward (digits 2 and 3)
and two back (digits 1 and 4).
This arrangement is most common in
arboreal species, particularly
those that climb
tree trunks or clamber through
foliage. Zygodactyly occurs in the
woodpeckers and
flickers,
nuthatches, and
parrots.
Heterodactyly is like
zygodactyly, except that it is
digits 3 and 4 that point forward
and digits 1 and 2 that point
back. This is only found in
trogons.
Other terms
An excess of digits is called
hyperdactyly or
polydactyly, such as in
the extremely rare case that a
person has six fingers or toes
on a single hand or foot.
A lack of digits not caused by
an
amputation is called
hypodactyly.
Ectrodactyly is the
congenital absence of all or part
of one or more fingers or toes.
This term is used for a range of
conditions from aphalangia
(in which the some of the
phalanges or finger bones are
missing), to adactyly (the
absence of a digit).
