The pentadactyl limb has 5 digits on the hand and foot. It also has a specific pattern of bones. The pentadactyl limb is common to humans, other mammals (although whales and dolphins have lost their hind limbs), birds, dinosaurs, and other reptiles and amphibians. Many vertebrates have a very similar bone structure despite their limbs looking very different on the outside. This structure is known as the pentadactyl limb – five fingered. This suggests that many vertebrates descended from the same common ancestor. One of the clearest examples of homology is shown by the pentadactyl limb it is found in all four classes of terrestrial vertebrates (amphibians, reptiles, birds and mammals) and can even be traced back to the fins of certain fossil fishes from which the first amphibians are thought to have evolved. The limb has a single proximal bone (humerus), two distal bones (radius and ulna), a series of carpals (wrist bones), followed by five series of metacarpals (palm bones) and phalanges (digits). Throughout the land forms the structure of the pentadactyl limb is fundamentally the same. But in the course of evolution, these fundamental structures have been modified and adapted for different functions, in some cases involving severe structural modifications. This phenomenon is clearly shown in the forelimbs of mammals. For example: The monkeys forelimbss and fingers are elongated to form a grasping hand admirably suited for swinging from branch to branch. But the most striking modification is seen in the bat whose forelimb has been turned into a wing by great elongation of four of the digits: the hook-like first digits remains free and is used for hanging from trees' the remainder support the skin of the wing. Through serving widely different functions, all limbs are plainly recognisable as modification of the idealised pentadctyl limb and are clearly homologous.
To read more on Pentadactyl limbs visit the natural history museum website : - http://www.nhm.ac.uk/nature-online/evolution/what-is-the-evidence/morphology/pentadactyl-limb/
To read more on Pentadactyl limbs visit the natural history museum website : - http://www.nhm.ac.uk/nature-online/evolution/what-is-the-evidence/morphology/pentadactyl-limb/