Decommissioning the dingo barrier fence has been suggested to reduce destructive dingo control and encourage a free transfer of biota between environments in Australia. Yet the potential impacts that over a century of predator exclusion might have had on the population dynamics and developmental biology of prey populations has not been assessed. We here combine demographic data and both linear and geometric morphometrics to assess differences in populations among 166 red kangaroos (Osphranter rufus)—a primary prey species of the dingo—from two isolated populations on either side of the fence. We also quantified the differences in aboveground vegetation biomass for the last 10 years on either side of the fence. We found that the age structure and growth patterns, but not cranial shape, differed between the two kangaroo populations. In the population living with a higher density of dingoes, there were relatively fewer females and juveniles. These individuals were larger for a given age, despite what seems to be lower vegetation biomass. However, how much of this biomass represented kangaroo forage is uncertain and requires further on-site assessments. We also identified unexpected differences in the ontogenetic trajectories in relative pes length between the sexes for the whole sample, possibly associated with male competition or differential weight-bearing mechanics. We discuss potential mechanisms behind our findings and suggest that the impacts of contrasting predation pressures across the fence, for red kangaroos and other species, merit further investigation.

The structure and material properties of different foods are widely considered to be reflected in the mechanics of the vertebrate skull. In this thesis, the relationship between feeding ecology and cranial morphology is examined in extant kangaroos and relatives. Geometric Morphometrics (3D shape analysis) and Finite Element Analysis (a form of computational biomechanics) were employed in order to identify the influences that the physical properties of vegetation, and behaviours involving food procurement, have on the shape and structure of the cranium.

The thesis focusses on the Macropodiformes, a sub-order of herbivorous diprotodont marsupials that includes three extant families: kangaroos and wallabies (Macropodidae), bettongs, potoroos, and rat-kangaroos (Potoroidae), and the musky rat-kangaroo (Hypsiprymnodontidae). This clade is represented by a diverse array of extant species from which to draw known ecology and diet across a broad range of body sizes. An initial interspecific study on sixteen macropodiform species found that feeding ecology is clearly associated with the relative lengths of the muzzle and zygomatic arch. Species that bite harder with the anterior dentition on more resistant foods possess a shorter muzzle and longer zygomatic arch.

By applying these methods to three closely related pademelon (genus: Thylogale) taxa, biomechanical performance during anterior biting was also found to reflect the mechanical properties of their respective diets at the subspecies scale. A diet dominated by more resistant vegetation was again represented by a shorter, more robust cranium, while a longer, more gracile cranium was observed in species that either bite into softer foods or employ cervical musculature to obtain more vegetation via tension (plucking), thus not requiring harder bites.

Wombats and koalas were then incorporated into a sample of other medium to large macropodiform species to test the viability of these previous findings at a broader scale. The results were then used to suggest the potential feeding ecology of an extinct species: the giant short-faced kangaroo, Simosthenurus occidentalis. Diet was clearly associated with palatodental arrangement across these species. However, muzzle length was not determined by diet, as in the previous chapters, but rather was associated with the hardest bites required of a species within its particular niche. A combination of cranial features and dental arrangements indicate that S. occidentalis was likely a browser, capable of consuming tough, bulky vegetation.

The findings of this thesis suggest that craniofacial morphology is intimately linked with dietary ecology among these species and may be used to infer the potential feeding behaviours and diet of rare or remote marsupial herbivore species for conservation and management strategies and also of extinct species for inferring their paleoecology. The relationships identified here could be applicable to other herbivorous taxa and used in tandem with microwear and stable isotope analyses to draw more robust conclusions, regarding feeding ecology and behaviour.

Potoroid marsupials (bettongs and potoroos of the family Potoroidae) are considered ecosystem engineers because of the roles they play in maintaining biodiversity. However, severe declines since European arrival have necessitated intense conservation efforts. Vital to these efforts is an understanding of the physical challenges that define their niches. The mechanical properties of their foods, such as toughness and stiffness, represent a physical interface with the environment that can contribute to quantitatively defining their niches. Here, we provide mechanical property data from wild bettong and potoroo foods, such as roots and tubers, fruit, fungi, invertebrates, seeds, and leaves. Toughness ranged from approximately 56.58 J/m² (fungal sporocarp of Descolea sp.) to 2568.15 J/m² (tubers of the blue yam, Brunoniella australis). Similarly, stiffness of the wild foods ranged from 1.15 MPa for Descolea sp. to 30.4 MPa for B. australis. However, the mechanical demands of accessing the kernels from within the shells (testae) of sandalwood and quandong (Santalum spp.) seeds far exceed measurements of any foods tested. We also tested some farmed foods, alongside inclusion of data from previous studies. Taken together, these data can also improve selection of comparable foods in designing diets for potoroids, and other species, in captivity.