Figure 2. A in Functional morphology of neck musculature in the Tyrannosauridae (Dinosauria, Theropoda) as determined via a hierarchical inferential approach

Figure 2. A, inference of muscle function for turning the head in extant animals. Axes represent levels of corroboration of muscle topological and kinematic morphology, physiology and observed behaviour. The volume subtended by these levels of certainty is the behavioural inference space for the muscle. The muscles m. transversospinalis capitis lateralis and m. complexus, homologous and present in crocodilians and birds, respectively, are depicted as examples with different levels of corroboration along the axes and more or less certain inference of function. Physiological activity is shown as confirmed by electromyography in birds, but only hypothesized in crocodilians. B, inferring the function of m. complexus for turning the head in tyrannosaurids. Axes represent levels of inference (Witmer, 1995) for morphology and physiology, and level of inference for kinematic action of the muscle based on its reconstructed morphology (see text for explanation). Because physiological muscle function during movements is corroborated in only one pole of the extant bracket, and the physiology does not leave osteological correlates, a Level II′ inference is the best possible for the extinct taxon .