
Bird, Pterosaur, & Bat
forelimbs as analogous Wing
Structures
Bird,
Pterosaur, and Bat forelimbs are homologous as
limb structures, with respect to the
sequential relationship of humerus, radius, ulna,
and digits as
inherited independently from flightless ancestors.
Forelimbs are analogous
as flight structures, and have evolved
independently in each group. The digits are arrayed in
radically different patterns in the flight surfaces. The bird
wing is supported by the entire forearm. The Pterosaur has a
single Brachiopatagium extending from the 4th digit
to the hindlimbs, whereas the Bat has a Dactylopatagium supported
by the 2nd-5th digits, and a Plagiopatagium between
the 5th digit and the hindlimbs. Pterosaurs and Bats both have
a Propatagium extending from the wrist to the neck,
but in the former it is supported by a novel bone.
Text © 2025 by Steven
M. Carr