Ben Tapley, curator of reptiles and amphibians at ZSL, which runs the central London zoo, said: "They may be tiny enough to sit on your fingertip, but their arrival represents a huge step forward for an amphibian facing an uncertain future."

ZSL said no other zoo or institution was known to keep the species.

It was only described by scientists in 2018. Fully grown, the frogs weigh less than 1.75g.

ZSL said almost nothing was known about them when they arrived, and keepers have since developed breeding techniques that are being shared with the CSIR-Forestry Research Institute of Ghana's breeding centre in Kumasi.

The aim is to build up a population in Ghana that could be released into the wild.

Ghanaian conservationist Caleb Ofori-Boateng, who helped identify the species, named it after his mother, Afia Birago.

"I named this frog after my mother so that her legacy would live on," he said.

"Thanks to this breeding programme, it will. Her name will be linked to a species we saved, not one we lost."

The births follow the zoo's success last November in breeding the Atewa slippery frog, another critically endangered species from the same forest, which had also never been bred in captivity before.

Listen to the best of BBC Radio London on Sounds and follow BBC London on Facebook, external, X, external and Instagram, external. Send your story ideas to [email protected], external