More than a third of species assessed in a major international biodiversity study are threatened with extinction, scientists have warned. Out of the 47,677 species in the IUCN Red List of Threatened Species, 17,291 were deemed to be at serious risk. These included 21% of mammals, 30% of amphibians, 70% of plants and 35% of invertebrates. Conservationists warned that not enough was being done to tackle the main threats, such as habitat loss. "The scientific evidence of a serious extinction crisis is mounting," warned Jane Smart, director of the International Union for the Conservation of Nature's (IUCN) Biodiversity Conservation Group.