An international team of scientists says it has found a "lost world" in the Indonesian jungle that is home to dozens of new animal and plant species.
"It's as close to the Garden of Eden as you're going to find on Earth," said Bruce Beehler, co-leader of the group.
The team recorded new butterflies, frogs, and a series of remarkable plants that included five new palms and a giant rhododendron flower.
The survey also found a honeyeater bird that was previously unknown to science.
The research group - from the US, Indonesia and Australia - trekked through an area in the mist-shrouded Foja Mountains, located just north of the vast Mamberamo Basin of north-western (Indonesian) New Guinea.
The researchers spent nearly a month in the locality, detailing the wildlife and plant life from the lower hills to near the summit of the Foja range, which reaches more than 2,000m in elevation.
"It's beautiful, untouched, unpopulated forest; there's no evidence of human impact or presence up in these mountains," Dr Beehler told the BBC News website.
"We were dropped in by helicopter. There's not a trail anywhere; it was really hard to get around."
FOJA MOUNTAINS SURVEY
See more of the plants and animals found by the team
He said that even two local indigenous groups, the Kwerba and Papasena people, customary landowners of the forest who accompanied the scientists, were astonished at the area's isolation.
"The men from the local villages came with us and they made it clear that no one they knew had been anywhere near this area - not even their ancestors," Mr Beehler said.
Unafraid of humans
One of the team's most remarkable discoveries was a honeyeater bird with a bright orange patch on its face - the first new bird species to be sighted on the island of New Guinea in more than 60 years.
The researchers also solved a major ornithological mystery - the location of the homeland of Berlepsch's six-wired bird of paradise.
First described in the late 19th Century through specimens collected by indigenous hunters from an unknown location on New Guinea, the species had been the focus of several subsequent expeditions that failed to find it.
On only the second day of the team's expedition, the amazed scientists watched as a male Berlepsch's bird of paradise performed a mating dance for an attending female in the field camp.
It was the first time a live male of the species had been observed by Western scientists, and proved that the Foja Mountains was the species' true home.
"This bird had been filed away and forgotten; it had been lost. To rediscover it was, for me, in some ways, more exciting than finding the honeyeater. I spent 20 years working on birds of paradise; they're pretty darn sexy beasts," Dr Beehler enthused.
The team also recorded a golden-mantled tree kangaroo, which was previously thought to have been hunted to near-extinction.
Mr Beehler said some of the creatures the team came into contact with were remarkably unafraid of humans.
Two long-beaked echidnas, primitive egg-laying mammals, even allowed scientists to pick them up and bring them back to their camp to be studied, he added.
The December 2005 expedition was organised by the US-based organisation Conservation International, together with the Indonesian Institute of Sciences.
The team says it did not have nearly enough time during its expedition to survey the area completely and intends to return later in the year.
The locality lies within a protected zone and Dr Beehler believes its future is secure in the short term.
"The key investment is the local communities. Their knowledge, appreciation and oral traditions are so important. They are the forest stewards who will look after these assets," Dr Beehler told the BBC.
A summary of the team's main discoveries:
- A new species of honeyeater, the first new bird species discovered on the island of New Guinea since 1939
- The formerly unknown breeding grounds of a "lost" bird of paradise - the six-wired bird of paradise (Parotia berlepschi)
- First photographs of the golden-fronted bowerbird displaying at its bower.
- A new large mammal for Indonesia, the golden-mantled tree kangaroo (Dendrolagus pulcherrimus)
- More than 20 new species of frogs, including a tiny microhylid frog less than 14mm long
- A series of previously undescribed plant species, including five new species of palms
- A remarkable white-flowered rhododendron with flower about 15cm across
- Four new butterfly species.