Fossilized bones of a previously unknown, long-extinct, small primate have been discovered in a coal mine in Lampang's Mae Moh district.
Geologists from the Department of Mineral Resources found the fossils in 2004 in the coal bed of the mine, owned by the Electricity Generating Authority of Thailand.
They spent four years verifying that the 13-million-year-old primate is a new species. It has been given the name Siamoadapis maemohensis.
The discovery will be published in the Journal of Human Evolution next month.
The newly discovered species is considered the smallest ancient primate, with a length of only 15 centimetres and weighing an estimated 500 grammes, team leader Yaowalak Chaimanee said.
''We have found four lower teeth, which helped us identify it as belonging to the family Sivaladapidae, which was found only in Asia _ mainly in China, Burma, India and Thailand _ from the mid-Eocene period [about 40 million years ago] until the lower Miocene [about eight million years ago],'' she said.
''With its small size, it would have probably have eaten insects and fruit.'' She said Siamoadapis maemohensis was a kind of Strepsirrhine. Lemurs and slow loris are believed to have developed from the species.
The discovery confirms the importance of the Mae Moh coal mine as a fossil site. The spot where the fossils were found is about two kilometres from the 43-rai area where a 13-million-year old snail fossil deposit was earlier found.
Sitting in layers of up to 12 metres deep, the site is believed to be the richest known freshwater snail fossil deposit in the world.