into the Early Cretaceous in Asia. The geologically youngest known tritylodontid is Fossiomanus from the 120 million years old Jiufotang Formation of China. During their evolution, the number of cynodont jaw bones reduced. This move towards a single bone for the mandible paved the way for other bones in the jaw, the articular and angular, to migrate to the cranium, where they function as parts of the mammalian hearing system. Cynodonts also developed a secondary palate in the roof of the mouth. This caused air flow from the nostrils to travel to a position in the back of the mouth instead of directly through it, allowing cynodonts to chew and breathe at the same time. This characteristic is present in all mammals. Taxonomy Richard Owen named Cynodontia in 1861, which he assigned to Anomodontia as a family. Robert Broom (1913) reranked Cynodontia as an infraorder, since retained by others, including Colbert and Kitching (1977), Carroll (1988), Gauthier et al. (1989), and Rubidge and Cristian Sidor (2001). Olson (1966) assigned Cynodontia to Theriodontia, Colbert and Kitching (1977) to Theriodontia, and Rubridge and Sidor (2001) to Eutheriodontia. William King Gregory (1910), Broom (1913), Carroll (1988), Gauthier et al. (1989), Hopson and Kitching (2001) and Botha et al. (2007) all considered Cynodontia as belonging to Therapsida. Botha et al. (2007) seems to have followed Owen (1861), but without specifying taxonomic rank. Phylogeny Below is a cladogram from Ruta, Botha-Brink, Mitchell and Benton (2013) showing one hypothesis of cynodont relationships: Distribution Cynodonts have been found in South America, India, Africa, Antarctica, Asia, Europe and North America. See also Permian–Triassic extinction event Prehistoric mammal Tetrapod Triassic-Jurassic extinction event References Further reading Davis, Dwight (1961). "Origin of the Mammalian Feeding Mechanism". Am. Zoologist, 1:229–234. External links Palaeos cynodonts Phylogeny of Theriodonts and Cynodonts Bennett and Ruben 1986. The Metabolic and Thermoregulatory Status of Therapsids BBC cynodonts Lopingian first appearances Extant Permian first appearances Fossil taxa described in 1861 Taxa named by Richard Owen