 Cabanac et al. (2009) argue that consciousness is unique to, and shared by all amniotes — the clade that includes all descendants of the common ancestor of living birds and mammals, including reptiles such as lizards, snakes, turtles and extinct animals such as dinosaurs, pterosaurs and pleseiosaurs (see http://tolweb.org/Amniota). On this hypothesis, only these animals, and not amphibians, fish, or any invertebrates, possess consciousness. Cabanac's argument is based on an explicit structural and functional theory of consciousness as a unified representational space, “an abstract private model of reality with four dimensions: quality, intensity, hedonicity and duration” (2009, p.268). Possessing this ability to model reality allows animals to simulate possible courses of action, using hedonicity (pleasure or pain) as a ‘common currency’ to evaluate and choose between actions based on expected consequences (which are based on prior experience). 