Ornithomimosaurs are a clade of Cretaceous theropods that are named due to their cranial and postcranial convergence with extant birds, particularly the palaeognaths, The ornithomimosaurs have attracted interest due to the cranial evolutionary trend from toothed to edentate inorphologies, and apparent link to herbivorous diets, There is also a trend of increasing cursoriality though the group, with the derived taxa developing robust, elongate legs, The morphological changes that occur throughout the group have never undergone rigorous functional analyses. In this thesis, the first finite element (FE) validation study was conducted comparing a specimen-specific FE model to an ostrich cranium to test how well strain magnitudes, ratios and orientations were replicated in silica, This FE study provides novel material property values via nanoindentationfor avian crania, and shows that soft tissues all play vital roles in strain modulation throughout the skull. Three well preserved skulls of omithomimosaurs (Garudimlmus, Struthiamimus and Ornithamimus) were CT scanned allowing detailed endocranial anatomy descriptions and retrodeformation ofthe skulls, Using the validation as the framework for the FE modelling of retrodeformed ornithomimosaur skulls, the effects of pecking and biting on the skulls were tested, Strain patterns are seen to shift from the posterior of the skull to the rostra, both within the ornithomimosaurs 'and Theropoda in general. The appendicular skeleton was also studied, with the forelimbs showing little variation in morphospaces between all omithomimosaurs, The hindlimbs show increasing elongation of the metatarsals through the clade, and ornithomimosaurs are distinct relative to most other theropods except two convergent (cranially and postcranially) ceratosaurs. The large palaeognaths do not occupy the same morphospace as the ornithomimosaurs, probably due to changes associated with the loss of a jail. The thesis provides a broad study of omithomimosaur function, an important step in better understanding the clade and the evolution of Theropoda.