Bats are 1/4 of the species on earth

Bats make up one-fourth of all the world's mammal species.

And in terms of sheer numbers, bats make up one-fifth of all mammals on earth.

Something to think about.

Here's an article by Annalee Newitz that begins to explain why:

So why do bats represent such a large number of mammals? Based on this study, published today in Proceedings of the Royal Society B, the researchers would argue it has to do with the animals' ability to diversify quickly in new environments — and that a big part of that is bats' extremely varied diets. Bat species range from nectar-sippers to insect-eaters and blood-munchers, and this allows them to spread into new territories.

http://io9.gizmodo.com/5862099/one-fifth-of-all-mammals-are-bats-heres-why