What is the smallest primate species?

The smallest primate species is Madame Berthe's mouse lemur, Microcebus berthae.

Madame Berthe's mouse lemur is a tiny nocturnal primate found in western Madagascar, especially around Kirindy Forest. Its average head-and-body length is about 9.2 centimeters, and its weight is around 30 grams, although body mass changes with season. A tail adds to its total length.

The species was discovered in 1992 and formally recognized after morphological and genetic studies distinguished it from other mouse lemurs. It is named after Berthe Rakotosamimanana, a Malagasy conservationist and primatologist who helped establish Madagascar's primate-research community.

Mouse lemurs feed on fruit, flowers, tree gum, sugary insect secretions, arthropods, and small vertebrates. Their small size does not make them harmless: predators include owls, snakes, and other forest animals. The species is Critically Endangered because deforestation, slash-and-burn agriculture, illegal logging, and charcoal production are destroying its specialized habitat.

A pygmy marmoset is also extremely small, but it is larger than Madame Berthe's mouse lemur.