Australia: The Land Where Time Began

A biography of the Australian continent 

Anatomy Based Relationship - Brain anatomy

The relationship between marsupial groups, such as the Diprotodontia and the Polyprotodontia, that appear similar can be distinguished by studying the links between the 2 halves of the forebrain. In placentals there are 3 commissures in their brains, nerve tracts linking the 2 halves of the brain. The 2 linking the hemispheres of the forebrain are the larger anterior commissure, also linking the 2 olfactory lobes in the forebrain, and the smaller hippocampal commissure (Johnson, 1977). The corpus callosum links the 2 halves of the cerebral cortex. The corpus callosum is lacking in marsupials and monotremes. Among the marsupials, the Diprotodontidae have a tract of nerve fibres, the faciculus aberrans, that extends the links of the anterior commissure to link the halves of the cerebral cortex. The Caenolestidae lack this tract, which supports the suggestion that their dentition, similar to that of the Diprotodonts, was probably a case of their dentition arising independently. At the time of writing the brain of Dromiciops had not been studied.

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.