An expedition to the island of New Guinea in the Pacific has rewarded intrepid researchers with three brand new species of tree frogs.

The new species, all members of the Litoria tree frog family, are incredibly rare, as scientists have only seen each of the species just once. They have been described for the first time in Zootaxa.

First up is Litoria pinocchio, which on first impression looks like a typical tree frog. On closer inspection, however, it has a small fleshy “rostral” spike, around 2.5 millimeters, protruding from its nose. Litoria vivissimia, which translates as “cheeky monkey”, has a similar protuberance on its snout.

“It’s pretty obvious how we came up with the name Litoria pinocchio – it refers to the distinctive spike between the frog’s nostrils,” said Dr Paul Oliver of Griffiths University, senior curator of Queensland Museum and lead author of the study.

“And Litoria vivissimia translates to ‘cheeky monkey’ – we have probably walked past dozens of them but have only ever seen one. We think they are probably up there in treetops laughing at us.”

They are not the first tree frogs found with these rostral spikes, but the size, structure, and degree of sexual dimorphism – the difference in appearance between males and females of the same species – varies across the Litoria family. 

"In four species the nose is actually erectile – sometimes it sticks out nearly straight from the snout, while sometimes it hangs loosely. This suggests these spikes really do serve a purpose," Dr Oliver told IFLScience. 

"In these four species, only male frogs are known to have an erectile nose. That tells us that selection is acting on the sexes to look different – like a male and female peacock."

One idea posited suggests the nose spike may be an indicator of fitness and females choose the males with the longest spike, however, Dr Oliver pointed out this theory isn't supported by studies on breeding choruses, where they found the females weren't choosing those with the longest spikes over other males.

"My preferred hypothesis is that it is for species recognition – in a noisy chorus of treefrogs around a pond – having a little spike on your snout might be a great way for females to confirm they have selected the right species of frog to mate with," Dr Oliver said. " The more prominent (erectile) it is, the harder it might be to mix things up."

The third frog is a parachuting frog, a type of frog that lives high in the treetops and leaps into the air, splaying its webbed feet to control its glide to neighboring tree branches, or occasionally, the ground.

The researchers described it as a large green frog with violet thighs, and named it Litoria pterodactyla. It's named after Pterodactylus, the first flying reptile, which itself comes from the Greek for "winged finger".

Indonesia, and New Guinea, in particular, is a biodiversity hotspot for frogs, with numerous new species described in the last 10-20 years. L. pinocchio was discovered in the Foja Mountains in northern Papua Province, the western side of New Guinea island that is administered by Indonesia. L. vivissimia was found in the mid-montane mountains of the Central Cordillera, the New Guinea Highlands also in Papua. It is morphologically similar to another known species of Litoria, L. pronimia, but was found 1,000 meters (3,280 feet) higher than any known locale for that species. L. pterodactyla was found in the hill forests in Western Province, Papua New Guinea, the independent country on the eastern side of the island.

"New Guinea is very, very wet. Some places get around 8 meters of rain a year – that is great for frogs," Dr Oliver explained to IFLScience. "[It] also has lots of mountains – this has provided opportunities for frogs to adapt to different climates and become isolated and diverge into different species. As a result, New Guinea has a remarkable frog fauna  – with over 400 species recognized, and many more awaiting description."

Although only just discovered, it's unlikely these frogs are in any danger just yet. "As far as we know each of the three frogs we describe has only been seen once by scientists.. [but] it is unlikely these three frogs are endangered as they live in areas with lots of forest and very few people."

However, "the forest of New Guinea are also coming under increasing pressure from agricultural development and clearing – and this will also pose an increasing threat to the survival of many species if not carefully managed."