A leaf-tail gecko, a golden-coloured skink and a boulder-dwelling frog are three new species discovered in a "lost world" in northern Queensland, Australia.

Scientists from James Cook University and National Geographic were dropped by helicopter in March this year into a remote mountain range on Cape Melville, to explore a pristine rainforest strewn with huge black granite boulders.

Within days the team had discovered three highly distinct new vertebrate species – believed to have been isolated for millions of years – as well as a host of other species that may also be new to science.

"Finding three new, obviously distinct vertebrates would be surprising enough in somewhere poorly explored like New Guinea, let alone in Australia, a country we think we've explored pretty well," said Dr Conrad Hoskin of James Cook University, who led the expedition together with Dr Tim Laman from Harvard University. "The top of Cape Melville is a lost world. Finding these new species up there is the discovery of a lifetime – I'm still amazed and buzzing from it."

Surveys had previously been conducted in the boulder fields around the base of Cape Melville, among "millions of giant, piled up boulders the size of houses and cars" but the plateau had remained largely unexplored, fortressed by a "monstrous wall" of boulders accessible only by helicopter.

The "primitive-looking" Cape Melville leaf-tailed gecko (Saltuarius eximius) measures 20cm and is believed to be a relic from a time when rainforest was more widespread in Australia. The species name translates as "exceptional", "extraordinary" or "exquisite", in reference to its unusual form and distinctiveness.

"The second I saw the gecko I knew it was a new species. Everything about it was obviously distinct," said Hoskin.

Herpetologist Dr Conrad Hoskin holds the Cape Melville leaf-tailed gecko, (Saltuarius eximius.) Photograph: Tim Laman

This gecko hides in the boulders in the day and emerges at night to hunt on rocks and trees. Highly camouflaged, its huge eyes and incredibly long and slender body and limbs are thought to be adaptations to life in the dimly lit boulder fields.

Patrick Couper, curator of reptiles and frogs at the Queensland Museum, and collaborator on the gecko's description, said: "The Cape Melville leaf-tailed gecko is the strangest new species to come across my desk in 26 years working as a professional herpetologist. I doubt that another new reptile of this size and distinctiveness will be found in a hurry, if ever again, in Australia."

The beautiful golden-coloured Cape Melville shade skink (Saproscincus saltus). Photograph: Conrad Hoskin

The beautiful golden-coloured Cape Melville shade skink (Saproscincus saltus) is also restricted to moist rocky rainforest on the plateau. It is also long-limbed, but unlike the gecko is active by day, running and jumping across the mossy boulders – the species name "saltus" means "leaping". This species is highly distinct from its relatives found in rainforests to the south.

Also discovered was the "fascinating" blotched boulder-frog (Cophixalus petrophilus). Its species name means "rock-loving" as it lives deep in the labyrinth of the boulder field where conditions are dark, cool and moist during the dry season. In the summer wet season, the frog emerges on the surface rocks to feed and breed in the rain.

The blotched boulder-frog (Cophixalus petrophilus) was among the three new vertebrate species discovered in Cape Melville, Australia. Photograph: Tim Laman

The frog has adapted to living in a boulder field with no water by laying eggs in moist rock cracks. "The tadpoles develop within the eggs, guarded by the male, until fully formed froglets hatch out," explained Hoskin.

The three new species have been named by Hoskin and described in the journal Zootaxa.