This isolated area of South-East Asia has yielded a type of ox or antelope, four species of deer, a rhinoceros and a loris - a shy and slow-moving primate - as well as frogs, reptiles and birds.
British scientists identified the unknown species of striped rabbit using DNA investigation to analyse its genes, which confirmed that the animal was different from, although related to, the only other known species of striped rabbit living in nearby Sumatra.
Rob Timmins, a British biologist working on a biodiversity programme organised by the Wildlife Conservation Society in America, spotted the carcasses of three freshly trapped striped rabbits in a meat market in the rural town of Ban Lak, in Laos.
Conservationists working in the Pu Mat Nature Reserve in Vietnam, which protects the isolated Annamite Mountains on the border with Laos, were later able to take photographs of the same species of rabbit in the wild, using automatic camera traps.
Dr Diana Bell, a rabbit expert at the University of East Anglia, confirmed that the specimens were a new species of striped rabbit closely related to but genetically different from the critically endangered striped rabbit of Sumatra, Nesolagus netsheri.
Dr Alison Surridge, a geneticist at the university, analysed the rabbit's DNA and concluded that it had been separated from its Sumatran cousin for at least eight million years, since a time when ice ages meant that sea levels were 150 metres lower than today, resulting in Sumatra, Java and Borneo being connected to the Asian mainland, the research-ers say in the journal Nature.
"It's a great surprise because when we first heard the rumours of the one in Laos we thought the Sumatran rabbit was extinct, but it, too, was later photographed by camera traps," Dr Bell said.
The Annamite rabbit closely resembles the Sumatran rabbit as both possess the black or dark brown stripes on the face and back - although the Annamite animal has a shorter stripe - as well as the distinctive red rump and short tails and ears. "What's remarkable is just how similar they are," Dr Bell said.
If the biologists manage to capture a live striped rabbit from Laos or Vietnam they expect to find a new species of flea living on it, Dr Bell said. "The Sumatran rabbit has a quite specific flea, and we expect the other striped rabbit to have its own," she said.