The Ordovician (pronunciation: /ɔːrdəˈvɪʃən/) is a geologic period and system, the second of six of the Paleozoic Era, that spans 41.2 million years from the end of the Cambrian Period 485.4 million years (Ma) ago to the start of the Silurian Period 443.8 Ma. The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods, respectively. Lapworth, recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, and placed them in a period of their own. It received international sanction in 1960, when it was adopted as