Created on 2016.07.29 324 views
Digital musculoskeletal reconstruction, and quantitative functional analysis of the skull of a small herbivorous dinosaur using Abaqus.  I have recently graduated from the University of Bristol with a Master's degree in Palaeobiology. For my thesis research project I studied a small herbivorous dinosaur, Psittacosaurus, and used sophisticated digitisation and analytical tools to resolve a hypothesis of convergent cranial function.  A recently published reconstruction of the jaw adductor musculature of the ornithischian dinosaur Psittacosaurus has included speculative features modelled upon a superficial similarity between psittacosaurs and psittaciform birds (parrots). In psittaciform birds, the neomorphic m. pseudomasster (mPSM) and m. adductor mandibulae externus ventralis (mAMEV) (which have an anterior position and anterodorsally inclined line of action) increase the leverage of the jaw and are thought to contribute to increased bite force. The existence of muscles similar to these has been suggested in Psittacosaurus to support a hypothesis of convergent cranial function.  We used computed tomography, digital restoration of skull anatomy and adductor musculature, and computational biomechanics to test this hypothesis, and demonstrated how the presence of anterodorsally inclined muscle loads influences stress, strain, deformation and estimated bite forces in the skull of Psittacosaurus. We used Abaqus to run finite element analysis of 56 uniquely loaded models, testing the effect of bite position, variation of active muscle groups, and variation of material properties of the skull. We find that the mPSM and mAMEV increase bite force at all three tested bite positions with an associated increase in cranial stress and deformation. The geometric morphometric informed sensitivity analysis of our finite element models show that variation of the bite position has the greatest effect upon loading-induced deformation; secondly, variation of the muscle load conditions and inclusion of the hypothetical muscles has a greater effect upon deformation than variation of the material properties of the skull. This study shows that there is clear anatomical and evolutionary evidence against the previously suggested enhancements to the jaw adductor musculature in psittacosaurs. Any hypothesised ecological convergence between psittacosaurs and psittaciform birds cannot be founded upon the basis of superficial or etymological similarity alone. Adam Taylor (M.Sc Palaeobiology, University of Bristol, graduated February 2016)
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