Forelimb

For example, the flipper of a turtle or of a dolphin, the arm of a human, the foreleg of a horse, and the wings of both bats and birds are ultimately homologous, despite the large differences between them.

The number of digits, their characteristics, as well as the shape and alignment of radius, ulna, and humerus, have had major evolutionary implications.

[3] A number of factors can influence the evolution of forelimb long bone shape, such as body mass, lifestyle, predatory behavior, or relative prey size.

Semi-fossorial and aquatic musteloid species tend to have short and robust forelimb long bones to deal with the strain from digging and swimming.

Predators hunting prey less than half their body weight tended to have longer and more slender forelimb long bones to improve energetic efficiency.

[3] Other hooves, like those of even-toed and odd-toed ungulates, and even the hoof-like foot of extinct hadrosaurs,[9] may be regarded as similar specializations.

To bear their immense weight, sauropods, the most derived being titanosaurs, developed a tubular manus (front foot) and gradually lost their digits, standing on their metacarpals.

[10] The stegosaurian forelimb has evidence for a sauropod−like metacarpal configuration[11] This was a different evolutionary strategy than megafaunal mammals such as modern elephants.

[12] Modern humans are unique in the musculature of the forearm and hand, though opposable thumbs or structures like them have arisen in a few animals.

[14] The ability to pronate the manus (hand) and forearm in therian mammals is achieved by a rounded head of the radius, which allows it to swivel across the ulna.

However, another distinct process may be identified, convergent evolution, by which the wings of birds, bats, and extinct pterosaurs evolved the same purpose in drastically different ways.