The Pentadactyl Limb (Edexcel GCSE Biology): Revision Note

The Pentadactyl Limb

• A pentadactyl limb is any limb that has five digits (e.g. five fingers or toes)

• Pentadactyl limbs are present in many species from many groups of organisms, including mammals, reptiles and amphibians

• In these different species, the pentadactyl limb has a fairly similar bone structure but sometimes fulfils quite a different function

  • For example, the human hand is used for handling tools and other objects but the pentadactyl limb of a bat (i.e. the bones that make up a bat's wing) is highly adapted for flight

  • Although the individual bones of the pentadactyl limb in these two species are very different shapes and sizes, their layout is almost exactly the same

• The high level of similarity in the bone structure of the pentadactyl limbs of mammals, reptiles and amphibians provides strong evidence that these groups all evolved from a common ancestor

  • Their limbs would most likely have had very different bone structures if they had all evolved from different ancestors

The bone structure of the pentadactyl limb of a human, a cat, a whale and a bat - although they have all evolved for different purposes, they all have the same basic layout