Extinction

Abstract

Abstract Based on fossil mammals from North America, extinction rates since the last mass extinction, but before human influences, are estimated at 0.4 species/species/million years, which implies a species typically persisted for about 2.5 million years. The background extinction rate has been punctuated by mass extinctions, which are defined as more than 75% of species in the fossil record going extinct over a relatively short period of time, the last of which was 66 million years ago. Over the past 50,000 years humans have caused extinctions of at least 30% of large mammals, and at least 30% of Pacific island bird species. Over the past 500 years, between 1% and 5% of all remaining vertebrates on continents have been lost, which is 50 to 250 times faster than the estimated background rate of fossil mammals and implies that we will reach mass extinction levels within a few thousand years. This time will be shorter if current extinction rates are underestimated, or rates increase in the future.