Brazilian Journal of Nature Conservation It seems likely that these unknown species will be rare and threatened with extinction. If they were not rare, then scientists would likely already have found and described them. Indeed, science may not discover them before they go extinct. hese questions seem especially pressing in 2010, the International Year of Biodiversity, and given the commitments countries have made to document and protect biodiversity in the Convention on Biodiversity. We address these issues for a sample of lowering plants and three vertebrate groups: amphibians, birds, and mammals. Using methods developed elsewhere (Joppa et al. 2010), we predict the likely numbers of missing species. We show that while the catalogues of all Brazil’s birds and mammals are likely nearly complete, the numbers of Brazil’s amphibians may increase by 15% and the numbers of just endemic lowering plants by ~10 to ~50%. How Many Endangered Species Remain to Be Discovered in Brazil? Stuart L. Pimm 1, *, Clinton N. Jenkins 2 , Lucas N. Joppa 3 , David L. Roberts 4,5 & Gareth J. Russell 6,7 1 Nicholas School of the Environment, Duke University, PO Box 90328, Durham, NC 27708, USA 2 Department of Biology, 1210 Biology-Psychology Building, University of Maryland, College Park, MD 20742, USA 3 Microsot Research, 7 J J homson Avenue, Cambridge, CB3 0FB, UK 4 Durrell Institute of Conservation and Ecology, School of Anthropology and Conservation, University of Kent, Marlowe Building, Canterbury, Kent, CT2 7NR, UK 5 Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK 6 Department of Biological Sciences, New Jersey Institute of Technology, Newark, NJ 07102, USA 7 Department of Biological Sciences, Rutgers University, Newark, NJ 07102, USA Abstract How many species are likely as-yet unknown to science? Even in relatively well-known groups, there may be substantial numbers of such species. It seems likely that these unknown species will be rare and threatened with extinction. Indeed, science may not discover them before they go extinct. We address these issues for a sample of endemic flowering plants and three vertebrate groups: amphibians, birds, and mammals, all from Brazil. We predict the likely numbers of missing species from models of the declining numbers of species described per five-year interval. The raw numbers increase over time, so we must scale these by the taxonomic effort. We show that while the catalogues of birds and mammals are nearly complete, the numbers of amphibians may increase by 15% and the numbers of endemic plants by ~10 to ~50% depending on region. These percentages may still seem encouragingly low, given the complexities of studying a country as large as Brazil, with its extraordinary diversity, and with many of its regions large and still poorly explored. What is more worrying is that these numbers of as-yet unknown species are broadly the same as the percentages of species that are presently considered threatened with extinction. That is, we know only half of the species in danger of extinction – and our knowledge of even those species has mostly been acquired in the last three decades. Key words: Brazil, Biodiversity, Unknown Species, Endangered Species, Amphibians, Birds, Mammals, Flowering Plants. *Send correspondence to: Stuart L. Pimm Nicholas School of the Environment, Duke University, PO Box 90328, Durham, NC 27708, USA E-mail: stuartpimm@me.com Introduction Brazil has extraordinary biodiversity with a greater number of terrestrial species of well-known taxa than most other countries in the world. It is likely to be comparably richer in the taxa that are poorly known, too. he range of habitats, which include the moist forests of the Amazon and the Mata Atlântica, as well as drier habitats and wetlands, surely guarantee that. Brazil also has large numbers of endangered species too, a consequence of extensive habitat destruction. hese factors, combined with the remoteness of much of the country, beg our asking: how many species are likely as-yet unknown to science? Even in relatively well-known groups, there may be substantial numbers of such species. Natureza & Conservação 8(1):71-77, July 2010 Copyright© 2010 ABECO Handling Editor: Maria Alice S. Alves doi: 10.4322/natcon.00801011 Research Letters