Cranial Morphology and Function of Diprotodon
This project is work from my PhD. Diprotodon optatum is the largest marsupial known and became extinct about 45,000 years ago. Using CT scanning and an engineering technique called finite element analysis (FEA) I am investigating the structure and function of the extensive cranial sinuses. Another aspect of this project is predicting the bite force and feeding biomechanics to explore the diet and behaviour of these animals.
Cranial Morphology, Biomechanics and Diet of Marsupial Herbivores
Marsupial herbivores come in many shapes and sizes, from hopping kangaroos to lumbering wombats. Studies on teeth, dentaries and jaw adductor muscles indicate that marsupial herbivores exhibit different specializations for grazing and browsing, including hypsodonty, molar progression and high bite forces. However, the relationships between skull morphology, biomechanical performance and diet are still relatively unknown. This research aims to investigate the interaction between biomechanical and non-biomechanical factors, including the lifestyle of the animal and its environment, in selection for skull morphology to meet multiple functional demands. In accordance with previous studies, results show the mammalian skull may not be optimized solely to resist forces generated during feeding.
Figure: Predicted distribution of stress across the cranial models of the (A) common wombat (V. ursinus), (B) koala (P. cinereus), (C) red kangaroo (M. rufus), and (D) swamp wallaby (W. bicolor).
Figure: Predicted distribution of stress across the cranial models of the (A) common wombat (V. ursinus), (B) koala (P. cinereus), (C) red kangaroo (M. rufus), and (D) swamp wallaby (W. bicolor).
Sinus Morphology of Marsupial Megafauna
Cranial sinuses are air-filled cavities resulting from the resorption and deposition of bone through pneumatisation in response to biomechanical stress. The morphology of a pneumatic bone represents an optimisation between strength and being light weight. Marsupial megafauna are "airheads" in that most of their skull is composed of very large air sinuses, and their brains are relatively small compared to the overall size of the skull. The size and morphology of the sinuses changes with the size of the animal and the morphology of the skull. Using CT scans to reconstruct the skulls and estimate the volume of the sinuses and brains we can get a better understanding of their size, morphology and evolution.
Figure: Three-dimensional reconstructions of Diprotodon optatum (A-B), Zygomaturus tasmanicum (C-D), Neohelos stirtoni (E-F) and Propalorchestes sp. (G-H) showing the extent of the auditory, squamosal, parietal and frontal sinuses in blue, and brain endocast in red. Skulls are shown in dorsal (A, C, E, G) and lateral (B, D, F, H) views. Scale bars represent 10 cm.
Figure: Three-dimensional reconstructions of Diprotodon optatum (A-B), Zygomaturus tasmanicum (C-D), Neohelos stirtoni (E-F) and Propalorchestes sp. (G-H) showing the extent of the auditory, squamosal, parietal and frontal sinuses in blue, and brain endocast in red. Skulls are shown in dorsal (A, C, E, G) and lateral (B, D, F, H) views. Scale bars represent 10 cm.
3D Visualisation and Reconstruction
Using a combination of CT and MRI scanning, gross dissection and biomechanical modelling, we can visualize and investigate the function of a variety of soft- and hard-tissue structures.
Figure: Digital dissection of the temporalis muscle group in the common wombat. 3D PDF available |
Information gathered from extant animals can then be compared to fossil specimens, allowing the reconstruction of muscles and other soft-tissue structures, which are rarely preserved in fossils.
Figure: Digital reconstruction of the jaw adductor musculature in the Diprotodon |
Reconstructing Rangea
Rangea is the type genus of the Rangeomorpha, an extinct clade near the base of the evolutionary tree of large, complex organisms which radiated during the late Neoproterozic. The discovery of three-dimensionally preserved specimens from Farm Aar in southern Namibia reveal the internal and external features of these animals, permitting new interpretations of Rangea morphology and lifestyle. Using microCT, synchrotron and surface scanning technology, we are examining the structure of Rangea to develop new interpretations of its morphology.
Figure: A surface scan of Rangea
Figure: A surface scan of Rangea
