A frog discovered in Papau New Guinea measuring less than 8mm long has been named the world's smallest vertebrate.

At an average of just 7.7mm (0.27 inches) long, the tiny black and red frog, named Paedophryne amanuensis, was discovered by scientists sitting on a leaf in the tropical island of Papau New Guinea.

It can now claim to be world's smallest vertebrate - animals with a spine - ousting the Paedocypris progenetica, an Indonesian fish averaging more than 8mm, from the record.

The scientists who discovered the minuscule frog also found a slightly larger species of frog named Paedophryne swiftorum, which measures at an average length of 8.5mm.

It is no surprise that the tiny amphibians proved to be especially difficult to find. Scientists located the creatures in 2010 by listening to the males' high-pitched mating call, a tricky task as they are especially hard for humans to hear.

"It's a great find," says Louisiana State University's Chris Austin in a statement, who made the discovery.

"New Guinea is a hotspot of biodiversity, and everything new we discover there adds another layer to our overall understanding of how biodiversity is generated and maintained."

The Paedophryne amanuensis has been named the world's smallest vertebrate despite the existence of the male Photocorynus spinicep, a species of anglerfish, which measures at just over 6mm.

This is because as they have no stomachs, they spend their lives living as a parasite to the larger female of the species, who measure up to 50mm long, meaning their inclusion in the contest is disputed.