Scientists Tuesday made a rare live addition to the order of primates, unveiling two new species of mouse lemur -- tiny, big-eyed animals that inhabit the forests of Madagascar.

The find brings to 20 the known tally of mouse lemurs, nocturnal tree-dwellers that weigh less than a large apple.

Yet even as the two minute animals were recorded in the book of life, the scientists warned that one of them was teetering on the brink of extinction.

Primates are the well-studied family of mammals that includes humans, apes and monkeys, and the addition of new, living species to the list is rare.

Biologists from the United States, Germany and Madagascar compared DNA, body mass and length, skull and tooth size and coat colouring to declare Microcebus marohita and Microcebus tanosi to be separate species and to usher them into clan of mouse lemurs.

With a body length of about 13.5 centimetres (5.3 inches) M. marohita is now the largest of the known mouse lemurs. Adding its bushy tail, it is all of 28 cm (11.2 inches) long and tips the scales at 78 grams (2.8 ounces).

The brownish primate has relatively large hind feet but small ears, and was named after the Marohita forest in eastern Madagascar where it was discovered, the team wrote in the International Journal of Primatology.

Marohita means "many views" in Malagasy.

Its cousin, M. tanosi, also falls on the large side of the mouse lemur scale, with a nose-to-tail length of about 27 cm (11 inches) and a weight of 51.5 grams (1.8 inches).

Discovered in Madagascar's southeast Anosy region, M. tanosi has a reddish head, with brown fur, a lighter-coloured belly, and a stripe along the spine.

The animals were discovered in 2003 and 2007, but it has taken years to formally identify them as a separate species. They probably escaped notice as they are outwardly similar to other mouse lemurs.

The team warned in their study that the Marohita forest has been "seriously fragmented and destroyed" since its namesake lemur was discovered there 10 years ago.

"Thus despite its species name, this mouse lemur is threatened by ongoing habitat destruction and 'many views' of its members are unlikely."

The team wants the International Union for the Conservation of Nature (IUCN) to add M. marohita to its Red List of threatened animals, and says M. tanosi was likely to follow the same route.

"Field studies and additional regional surveys are... urgently needed to determine at least the geographic range and population status of these newly described species so that appropriate conservation measures can be implemented."

The IUCN says Madagascar's lemurs are among the most endangered animals on Earth, with 91 percent of the 100-odd species and subspecies threatened with extinction.

Deforestation and poaching are the main threats to lemur survival in the Indian Ocean country plagued by political instability since a coup in 2009.

The island nation has lost some 11 million hectares (27 million acres) of its forest cover in the last 20 years, according to the IUCN.

In a report last year, the agency said the rarest lemur, the northern sportive lemur, was down to 19 known individuals.

Due to Madagascar's geographical isolation, all of the island's primates are endemic, as are 90 percent of its plants and 80 percent of its amphibians and reptiles.

New animals are still being discovered there, and the number of identified lemur species has more than tripled in the past decade.