Natalie Warburton

An animal's interaction with its environment is facilitated by the complex workings of the musculoskeletal system via movement. An animal's method of moving through its environment is fundamental to its way of life, how it finds food, shelter, escapes predators, interacts with conspecifics, disperses or migrates. Musculoskeletal anatomy is well correlated with ecology; craniodental morphology is highly adaptive with respect to feeding strategy, while variation in postcranial anatomy reflects adaptation principally for locomotion. Marsupials and monotremes fill a diverse range of ecological niches that are reflected in a great diversity of structural forms. Patterns in the form and function of animals can inform our understanding of the evolution of diverse groups and the relationships between them. In this chapter, we consider examples of musculoskeletal anatomy of marsupials and monotremes that highlight patterns of both phylogenetic history and evolutionary adaptation.

Species in the extinct genus Bohra have been allied with living tree-kangaroos (Dendrolagus) on the basis of marked similarities in isolated craniodental and hind limb elements. Prompted by recent discoveries of the first near-complete Bohra skeletons in Pleistocene deposits in caves beneath the central Nullarbor Plain, south-central Australia, we compared the pedal morphology of tree-kangaroos with a range of terrestrial macropodines. Our objectives were to more clearly detail the key functional attributes of the Dendrolagus pes and to assess the likely arboreal adeptness of Bohra. Overall proportions of the calcaneum, talus, cuboid and metatarsals, as well as the morphology of their articular facets, suggest that the Bohra pes was specialised for enhanced mobility and flexibility, and thus well adapted to the functional demands of an arboreal environment. The presence of these Pleistocene species on the Nullarbor Plain indicates that tree-kangaroos had far broader geographic and climatic ranges than hitherto anticipated, and also demonstrates that the ‘Treeless’ Plain was not always treeless.