A Primate Presence in a Coal Mine
In the lignite layers of northern Thailand's Mae Moh Basin, miners uncovered fossils. They found the fossilized remains of a previously unknown primate, a creature that lived between 13.1 and 13.3 million years ago. This region, specifically the Mae Moh coal mine in Lampang province, has yielded one of the extensive Miocene vertebrate fossil records in all of Southeast Asia. The primate fossil from this site is a sivaladapid, a group of Asian adapiform primates known from the Eocene through the late Miocene. Named Siamoadapis maemohensis, this specimen is scientifically important because it is the first and only Miocene monkey relative discovered in the region.
The fossil itself is small, but it shows a distinct biogeographic province. The primate fauna of middle Miocene Thailand, which includes Siamoadapis, a loris, tarsiids, and hominoids, shows a composition similar to assemblages from southern China and the Indian subcontinent. Yet, the Thai fossils represent unique genera, suggesting the area had distinctive paleoenvironments. The collection and study of these fossils, including work by paleontologist Takeshi Setoguchi of Kyoto University, has helped define this unique ancient ecosystem. These collections are now part of the resources at Kyoto University.
Reconstructing an Ancient World
The Mae Moh Basin during the middle Miocene was a world unlike today. The presence of lignite, a soft brown coal, points to ancient swampy forests. The diverse collection of animal fossils found alongside Siamoadapis helps to build a more complete picture of this environment. The fauna includes otters, bear-dogs (amphicyonids), ancient elephants (deinotheres), rhinos, deer, and pigs.
This single primate specimen, Siamoadapis maemohensis, is distinguished from other Miocene sivaladapids by its smaller size and specific dental features. Its discovery expanded the known diversity of primates from this period and place. The acidic soils of tropical forests are generally poor at preserving fossils, which makes finds like this one especially informative. The presence of this sivaladapid indicates that Southeast Asia was a distinct ecological province during the middle Miocene. While large mammals from Mae Moh show connections to faunas in Pakistan and India, the smaller mammals, including primates, appear to be more localized and morphologically distinct.