How many mammal species are in the world?

While the number of species is under constant review, and any estimate at any given time is probably inaccurate, there are between 4500 and 5000 species of mammals. The latest available list from the Mammal Species of the World lists 4629 unique species.

These range from the smallest (shrews, pikas, and voles) to the largest (whales, rhinoceroses, elephants, and hippos).