An architectonic comparison of the ventrobasal complex of two Megachiropteran and one Microchiropteran bat: implications for the evolution of Chiroptera

The architectonic features of the thalamic ventrobasal complex (Vb) of two species of Megachiropteran (Grey-headed flying fox, Pteropus poliocephalus, and the Eastern tube-nosed bat, Nyctimene robinsoni) are compared with tho se of a Microchiropteran (Australian ghost bat, Macroderma gigas). The soma tosensory system was chosen for comparison as it represents a sensory syste m that has undergone analogous modifications in both Chiropteran lineages ( the evolution of the wing). The components of Vb were examined as there are taxon-specific features in this region of the brain. Within the Megachirop teran Vb, four subnuclei were recognized: the ventral posterior medial (VPM ), the ventral posterior lateral (VPL), the ventral posterior inferior (VPI ), and the basal ventral medial (VMb). In the ghost bat only VPM and VPL we re identified with certainty. No VPI was evident in the ghost bat, however a putative VMb was observed. Vb of the ghost bat also lacked the arcuate la mina, which distinguishes VPM from VPL in the Megachiropterans and many oth er mammals. These taxon-specific differences lend support to the proposal t hat the order Chiroptera has a diphyletic origin.