Yaowalak Chaimanee and a team of palaeontologists discover a new species in Lampang

Story by CHOMPOO TRAKULLERTSATHIEN and Photos by SUCHADA HONGSA

Fossilised molars of `Siamoadapis maemohensis' dating back 13 million years.

Yaowalak Chaimanee (2nd left) and her team of palaeontologists.

Walking is actually an integral part of Dr Yaowalak Chaimanee's working life. The farther she walks, the farther she is brought back to the lost world where a wide variety of ancient creatures once roamed.

Her latest walk at the desolate Mae Mo coal mine in Lampang province sets another milestone in palaeontology; it provides a missing link in a puzzle, and bridges a gap between the modern era and the ancient world dating back to the middle Miocene period - some 13 million years prior.

The veteran palaeontologist hit the jackpot once again as the barren site yielded an abundant fossilised assemblage of many species including four lower molars of an ancient primate. What at first appeared to be blackened wood-like clusters turned out to be crucial evidence - since they belong to the world's new genus and species of primate, which shares similarities with present lemurs now living in Madagascar. Palaeontologists named the fossil Siamoadapis maemohensis, meaning fossils of Siam primate found in the Mae Mo locality.

Yaowalak's discovery sheds new light on the primate kingdom, and confirms that Thailand was once home to this primate belonging to the Sivaladapidae family and infraorder adapiforms, found only in Asia since the Eocene period, around 40 million years ago, which became extinct during the late Miocene era, some eight million years earlier. The discovery of Siamoadapis maemohensis shows that the palaeoenvironment in Thailand during the Miocene Epoch was a tropical forest - with a more humid and less seasonal climate.

Yaowalak compared all of the new specimens found with fossils previously excavated in other parts of the world to make sure they carried distinctive characteristics, which would set them apart from former species. The lab results brought her tremendous happiness, since what she found wasn't expected so soon, and likely to take her entire working life to unearth.

"The chance to discover fossils of primates in Thailand is very slim since primates can live only in an environment, which we can not know for sure, that suits them best. The more we find, the more we will know about human evolution. However, there are still many missing links between modern mankind and their ancestors. This discovery is a good start for me to forge ahead and find the missing puzzles," said Yaowalak, who has excavated some 40 new species of ancient animals over the past 20 years.

Yaowalak Chaimanee in her lab in Bangkok.

`Siamoadapis maemohensis' shares some similarities with lemurs living in Madagascar.

To keep the world's palaeontologists abreast of the latest discoveries, Yaowalak's findings were recently published in the Journal of Human Evolution last April.

"I stumbled upon the fossils of this primate in 2004, and started studying it in 2005. It took two-and-a-half years for my article to be published since there are numerous palaeontological articles in the queue. All of the information I presented had to be carefully read and approved by three veteran palaeontologists from the journal. It was a long wait but definitely worth waiting for," she added.

According to some palaeontologists, middle Miocene strata in Thailand abounds with fossils of diverse mammals. Yet, 10 years prior, only a few isolate teeth of primates, identified as tarsier and loris, have been reported from the Li basin of Lamphun province. Recently, hominoid teeth have been excavated at the Chiang Muan basin in Phayao province, and allocated to the new genus known as Khoratpithecus. However, the apparent absence of Asian adapiform primates has long been enigmatic, simply because the slightly older and earlier fossil localities in India, Pakistan and China have yielded abundant samples of these primates. The discovery of new sivaladapid adapiforms from the middle Miocene epoch in Thailand significantly expands the geographical range and taxonomic diversity of the group.

"We once discovered fossils of apes in Phayao and Nakhon Ratchasima provinces four to five years ago. The discovery of Siamoadapis maemohensis yields the first fossils of a primate living during the Miocene epoch, which was initially found in Thailand and Southeast Asia, and revealing the diversities of this primate during ancient times," said Yaowalak, who is a palaeontologist at the Department of Mineral Resources, Palaeontological Section, Bureau of Palaeontology and Museum.

Based on her studies, Siamoadapis maemohensis is categorised in the class of strepsirrhines, or wet-nosed primate, which includes the present lemur found in Madagascar and the loris native to Southeast Asia. Its nose bears the most outstanding characteristic since it is adjoined to the upper lip. Its front and canine teeth are comb-like. Its mandible has a low corpus and low-crowned molars, and the depth of the jaw is relatively uniform.

Throughout time, fossils of the genus Sivaladapidae have been found in several Asian countries, including China, Burma, India and Pakistan.

Compared to other species of the sivaladapid group, Siamoadapis maemohensis is the smallest primate with an estimated body mass of 500 to 700 grammes. Analysing from its size and its characteristics of dentition, many palaeontologists believe that Siamoadapis maemohensis is a nocturnal animal that subsists on fruit, leaves and insects. Living in trees, the long-tailed primate has a keen sense of smell and a small brain, and is also considered a lesser developed primate.

According to Yaowalak, Mae Mo coal mine is the largest lignite deposit and the biggest coal mine in Thailand. It's about 17km long and nine kilometres wide, and its tertiary sediments are 800m thick. The tertiary deposits of the Mae Mo basin have been categorised into three formations: Huai King, Na Khaem and the Huai Luang formation. Fossils, including the remains of gastropods, fish, turtles, crocodiles, mammals and primates, are found in the Na Khaem formation. Over several decades, the only mammalian fossils that have been reported from the Mae Mo coal mine are proboscideas, rhinoceros, two carnivores and two rodents.

"The place where I found the fossils was at the edge of the tertiary deposit where the stream once flowed through. Animals would come to forage for food here so we found an agglomerate of fossils in this area, which belong to both small and large animals. Mae Mo coal mine is a wonderful palaeontological site and I do believe that there are more fossils to be dug up. And there is a high potential that they will be of the new species," she said, adding that two years ago a new species of a Malay bear and elephants with four tusks were also found at the site.

Although the Mae Mo site is a big and inestimable treasure trove for Yaowalak, it is not an easy task to find and dig up fossils in a short time since everything is now all black. Any successful exploration requires a keen eye to differentiate the bones covered in blacken soil, and a strong mind to brave the sweltering sun and putrid pit.

Yaowalak had to walk along a five-kilometre track each day, and repeat her trail on every other day to ensure she didn't leave any important clues behind. Furthermore, she had to race against time because the soft layers of coal sediments could crumble down at any time, and if that happened, it would mean her chance of discovering more fossils would be nil.

"Worse still is the ambiance around the coal mine. It's much like a lifeless land shrouded by an endless black stretch. There is not one single tree. It is so hot and dirty but I got used to it. My job was to keep scanning the grounds to locate the right spot where I could collect fossilised bones," she explained.

To make her mission easier, Yaowalak had to pinpoint certain areas where she wanted to walk, otherwise her walks would be aimless. First of all, she had to identify the type of soil before launching an excavation. A clay layer teems with fossils of shells, turtles, soft-shell turtles and crocodiles, while an organic layer is rich in fossilised plants and fossils of species that foraged for food near the stream. In the areas where coal isn't completely formed, it is abundant with fossils of a wide variety of animals including mammals.

"I can't walk randomly since this coal mine is so vast. The situation would be better if I could scope down my search. When the bones are identified at a certain spot, it has a high potential of holding ample fossils, and I can then concentrate my excavation there with the aid of a small knife to dig up the soil," she explained.

To save time, Yaowalak fills 20 bags of soil, totalling a weight of 400 to 500kg, taken from the site daily for farther study at a temporary outdoor laboratory. The soil is left to dry in the sun to get rid of the humidity, then soaked in water to separate clay from hard objects. A very fine mesh is used to sieve unwanted residue stuck on the bones. On the first day of filtering, small teeth from an unidentified species are left behind, and on the next day, unfamiliar molars with teeth appeared. All of the fossils were covered with special chemicals to maintain their durability. With the aid of a microscope, palaeontologists were ecstatic at their findings since they belonged to the primate. Deep down though, Yaowalak had hoped it would be a new species. Several months later, her hopes became true, after a study revealed the newly-discovered fossilised teeth and molars had no similarities to other primates found in other parts of the world.

"The dentition of a Siamoadapis maemohensis is extremely unique. Normally all animals have premolars with teeth smaller than its molars but this primate is different. The teeth on premolars are exactly like its molars," she explained.

It is difficult to imagine what this primate would look like by looking only at the fossils, so an image of the Siamoadapis maemohensis was drawn and painted by Mana Rakmanee, Yaowalak's colleague. He also sketched every detail of the four molars with the aid of a microscope.

"He had to use one eye to look at the fossils through a microscope and the other eye to draw what he saw. He did a very good job. All of his Siamoadapis maemohensis drawings appeared in the Journal of Human Evolution, which allows anyone interested in this topic the chance to learn more about this primate," said Yaowalak.

Though Yaowalak's several missions have been completed, she still has high hopes for her next excavation at the Mae Mo coal mine. She is looking forward to seeing her "ancestors".

"I really want to see fossils of apes at this site since it is considered the greatest culmination of exploration. Unbelievably, I once found fossils of apes at two other sites in Phayao and Nakhon Ratchasima provinces, close to this basin. I keep asking myself whether I'm a horrible excavator, or I just can't seem to hit the right target to find ape fossils here. But the situation is becoming more hopeful after we discovered one more species of primate."