LAUSR

We have analyzed the internal structure of the brain of the microbiotherian marsupial Dromiciops gliroides and compared it with the brains of American and Australian marsupials. Dromiciops does not have a fasciculus aberrans, but does exhibit other features of brain structure that are similar to diprotodontid metatherians (e.g., lamination of the lateral geniculate nucleus of the dorsal thalamus). Cortical organization in Dromiciops shows some similarities with that in Australian marsupial carnivores in that the proportional areas of isocortex devoted to somatosensory and visual function are similar in size to each other, and greater in area than that devoted to olfactory or auditory function. This points to similar sensory requirements for the foraging lifestyle of Dromiciops and small Australian marsupial carnivores, with isocortical specialization for somatosensation and vision. We also examined phylogenetic relationships of Dromiciops with extant marsupials based on maximum parsimony analysis using a soft body brain morphology-only matrix, representing 93 extant marsupial taxa. The results recovered Dromiciops as a sister group to the Australasian marsupial clade Diprotodontia.