An analysis of some thalamic projections to parietofrontal neocortex in the marsupial native cat, Dasyurus viverrinus (Dasyuridae).

Thalamocortical projections to parietofrontal neocortex in the marsupial native cat, Dasyurus viverrinus, were examined using the retrograde transport of horseradish peroxidase. The results show that the organisation in Dasyurus is similar to that reported in another Australian marsupial, the brush-tailed possum, Trichosurus vulpecula, and is different to that found in the primitive American form, Didelphis virginiana. In Daysurus, as in Trichosurus, the areas of neocortex receiving projections from the trigeminothalamic system do not appreciably coincide with those areas receiving input from the cerebellothalamic system. In Didelphis there appears to be complete overlap of these areas of motor and somaesthetic neocortex. These results suggest that the motor--somaesthetic organisation in Australian marsupials is divergent from the presumed stem pattern seen in the American forms. If the Australian marsupials, as is now believed, were isolated from the stem Polyprotodonta in the upper Cretaceous, it would appear that the Australian marsupials may have begun to develop certain aspects of their characteristic CNS configuration very early, as the oldest known marsupial fossils are not much older than this.