Information gleaned from the unique birth could now be vital in helping to prevent the species from becoming extinct.

The unnamed female is just 8cm from nose to tail and is living with her mother Tilly in the forest-like small mammal enclosure at the zoo.

The zoo became aware of the birth only when the tiny baby was spotted in the mother's pouch on 4 April.

"Within three months we began to see arms and legs poking out of the pouch," said Frank Wheeler, head keeper of small mammals at London Zoo.

Diet of grubs

"This meant the baby was becoming too big for its mother to hold within the pouch.

"From this point at around 30 June the young possum attached itself to its mother's thigh."

The baby, as yet unweighed, will be fed on a diet of grubs. If she grows to an average adult-size she will stand 25cm tall and weigh 360g.

London Zoo keepers have been trying to get her parents Billy and Tilly, both aged about four years old, to successfully mate since 1996.

The striped possum's natural habitat is the forests of Northern Australia and New Guinea.

It is endangered because these habitats are being destroyed to provide land for agriculture.

'Vital information'

Mr Wheeler said: "This is really a breakthrough and it's not just by good luck.

"So little is known about the breeding habits of the species that it has been months of careful planning which resulted in this successful birth.

"We are keen to study how the female will behave, to provide vital information to help the international protection of the species."

London Zoo has eight adult striped possums in total.

Poland's Poznan Zoo and Germany's Berlin Zoo are the only other European sites housing stripped possums.