Number of extinct species is an indicator of the ultimate effectiveness of responses to the threatened species indicator. But the threatened species indicator is a more useful single indicator of impacts on species diversity because it is forward-looking and less difficult to monitor. Total number of species and number of threatened species, preferably for all vascular plant and vertebrate animal classes. National data on threatened fishes are also available for many countries, but not reported by class, and usually for freshwater only. National data on total numbers of fish species are not as widely available.
Few countries have sub-national data.
Many countries hold the data, but for some, it is easier to obtain them from international sources. A Portable Dictionary of the Higher Plants. Cambridge University Press, Cambridge, United Kingdom. Margulis, Lynn, and Karlene V. Schwartz. An Illustrated Guide to the Phyla of Life on Earth.