Australia: The Land Where Time Began

A biography of the Australian continent 

Anatomy based relationships - Foot Structure

Based on foot structure, the Australian dasyurids and all American marsupials share a common feature of the hind foot, didactyly (separate digits) 5 separate subequal digits. Syndactyly (fused digits) occurs in all other Australian marsupials, in which the the first digit on the hind foot is reduced to a nubbin, and the 2nd and 3rd digits are partly fused together of equal size to the 5th digit. In some species, as the large kangaroos, the 4th digit is much larger and longer than the others, taking the main thrust when when the animal is jumping. Some species use the 2nd and 3rd digits for grooming. It is not known if they evolved for this function of as a result of reduction to allow faster running. The dentition of bandicoots (Peramelomorphia) is similar to that of carnivorous marsupials from both Australia and America, yet their foot structure is indistinguishable from that of Diprotodontia. Research has been finding evidence that the 2 groups probably acquired the structure independently. It has been found that the genetic control of this structure is very simple, so there it could easily have evolved more than once.

1. Chris Johnson, Australia's Mammal Extinctions, a 50,000 year history, Cambridge University Press, 2006
2. M.Archer, S.J. Hand & H. Godthelp in Hill, Robert S., (ed.), 1994, History of the Australian Vegetation, Cambridge University Press.
3. Tyndale-Biscoe, Hugh, 2005, Life of Marsupials, CSIRO Publishing.