Humerus midshaft histology in a modern and fossil wombat

Abstract

The common wombat (Vombatus ursinus) is equipped with a set of physiological and morphological adaptations suited to a fossorial lifestyle. These allow wombats to engage in efficient scratch-digging and maintaining a low basal metabolic rate while living underground. While bone microstructure has been described for several subterranean animals, wombat bone histology has received very little attention to date. Here, we present preliminary insights into bone histology in modern adult V. ursinus (Mt Fairy, NSW) and Pleistocene fossil Vombatus sp. (Bakers Swamp, NSW) midshaft humeri. The modern sample was well preserved, allowing us to identify varying bone tissue types (woven, parallel-fibered, lamellar). The sample showed vascularity composed of primary and secondary osteons, and simple longitudinal and radial vessels. We also observed evidence for Haversian remodelling (i.e. localised replacement of pre-existing bone) and coarse compact cancellous bone within the inner cortex of the diaphysis. The fossil histology was poorly preserved, but likely showed bone matrix organisation similar to the modern specimen. We use these preliminary data to discuss hypotheses for wombat forelimb biomechanical and physiological microscopic adaptation to a burrow environment. We encourage future intra-skeletal examination of microstructure in wombat populations to better inform their ecological adaptations and behaviour in palaeontological contexts.