A completely new family of rodents has been recognised to take account of a rat-like creature from Laos.
The animal has long whiskers, stubby legs and a tail covered in dense hair and was on sale in a hunters' market.
Dr Robert Timmins from the Wildlife Conservation Society saw that it was probably unknown to science and brought it to the attention of his peers.
Known by locals as Kha-Nyou, the rodent is said to be a nocturnal vegetarian that prefers the cover of the forest.
It also gives birth to one offspring at a time, rather than a litter.
"It was for sale on a table next to some vegetables," said Dr Timmins. "I knew immediately it was something I had never seen before."
Dr Mark Robinson, working with WWF Thailand, later discovered other specimens caught by hunters, and also identified bone fragments in an owl pellet.
Based on morphological differences in the skull and bone structure, coupled with DNA analysis, the authors estimate that the Kha-Nyou diverged from other rodents millions of years ago.
"To find something so distinct in this day and age is just extraordinary. For all we know, this could be the last remaining mammal family left to be discovered," Dr Timmins said.
The new species, Laonastes aenigmamus, is described in the recent issue of the journal Systematics and Biodiversity, by authors from WCS, The Natural History Museum in London, University of Vermont and WWF Thailand.