Dept. of Anthropology, Boston University
Saturday All day, Clinch Concourse
Among diprotodont marsupials, koalas (Phascolarctos) and wombats (Vombatus, Lasiorhinus) are sister groups within a clade that has kangaroos and phalangers as its phyletic sister. Both koalas and wombats are quadrupedal, but koalas are slower-moving — and unlike wombats, they spend long periods of time sitting upright while feeding and resting. Preliminary data nevertheless show that the size disparity between the bodies of the cervical vertebrae and the (larger) lumbar vertebrae is less marked in koalas than in wombats. By contrast, kangaroos show a much more marked caudad increase in vertebral body size than either koalas or wombats. This marked increase is seen in kangaroos that are both larger and smaller than koalas, and is therefore not due to allometry.
We suggest that these facts support our earlier inference from similar data on bovids— that locomotion, especially running, is a more important influence on the scaling of vertebral body size than posture is. This conclusion may have implications for our understanding of the surprisingly small lumbar vertebrae of early hominins.