Cracking the Ice Age in Thailand with Prehistoric Hyena Fossils 

A lecturer at the Department of Geology, Faculty of Science, Chulalongkorn University, has discovered teeth fossils of hyenas, orangutans, and several other mammals, aged between 200,000 – 100,000 years in a cave in Krabi. These form an important piece of evidence indicating that the South of Thailand was once large grasslands mixed with forests during the Ice Age and may have been a migration route for Homo erectus moving from Africa to the Java islands. 

When mentioning the climate and terrain of southern Thailand, many people think of hot, humid weather with heavy rainfall and dense forests filled with tall trees. But during the Ice Age around 200,000 years ago, this same area had completely different conditions – cold, dry climate with vast open grasslands, similar to the savannas we see today in Africa. 

A prehistoric story is now revealed from the “spotted hyenas fossils” found in a cave in Krabi.

“During the Ice Age, the world had a much colder climate. Glaciers spread to northern and central China, but our world was not entirely covered by glaciers. Thailand has no evidence of glaciers, no mammoths, but it had hyenas!” said Assoc. Prof. Dr. Kantapon Suraprasit from the Department of Geology, Faculty of Science, Chulalongkorn University.  

“The spotted hyena fossils are commonly found across Asia, including in China, Laos, Vietnam, and northern Thailand. Finding them in the South means that the spotted hyena spread to Thailand’s southern peninsula as well, indicating that this region used to have similar conditions to the savannas,” explained Assoc. Prof. Dr. Kantapon.  

In Thailand, there have been reports of hyena fossils discovered in several areas, such as at Phra Cave (Ban Fa Suai) in Chiang Mai, at Wiman Nakin Cave in Chaiyaphum, and at Bo Sai Khok Sung in Nakhon Ratchasima where a complete skull of a spotted hyena was found. However, no fossils of this species had ever been surveyed and discovered in the South until a team of paleontologists led by Assoc. Prof. Dr. Kantapon, in collaboration with the Department of Mineral Resources and the Krabi Cave Lovers Club, began pioneering surveys of prehistoric animal remains in southern caves. They discovered spotted hyena tooth fossils at Khao Yai Ruak Cave in Tambon Ao Luk Nuea, Ao Luk District, Krabi, in 2019, and most recently in December 2024, they found spotted hyena tooth fossils along with fossils of wild deer, orangutan, pig, porcupine, cattle, and buffalo at Khao Toh Luang Cave in Ban Chong Phli, Tambon Ao Nang, Mueang District, Krabi. 

These fossils are preserved at the Department of Mineral Resources as well as at Chulalongkorn University’s Geological Museum to be studied and researched under the project titled “Survey of Pleistocene Mammalian Fossils in Southern Thailand.”  

“Studying the past, comparing evidence with the present, to predict the future” is one of the roles of paleontologists, said Assoc. Prof. Dr. Kantapon. “We study prehistoric fossils, analyze the habitats and environments of prehistoric animals through geological analysis processes, search for answers from the past, compare them with present-day animals, to find answers on what will happen to our world in the future.” 

“When teaching, I tell students that we learn about the past from evidence in the present to predict events that will occur in the future. We cannot know about the past at all if we don’t have evidence that we find in the present. We can know how this fossil, this animal, lived in the past by using present-day animals as examples to compare with the habitats and environments where current animals live. When we learn the past from the present, we can link it to answer questions about the future, such as ‘when will the ice age cycle return?’ or ‘how will the climate change?’” 

Unlocking Prehistoric Secrets from Cave Sediments  

Assoc. Prof. Dr. Kantapon explained the fundamental principles in surveying and searching for prehistoric animal fossils that “Dinosaurs went extinct 66 million years ago. After that, the world was dominated by mammals. Therefore, the search for prehistoric animal remains in Thailand must be limited to areas where the rocks are younger than 66 million years old. The fossilization process takes hundreds of thousands or millions of years, sometimes several million years. Therefore, to find mammalian fossils, we must look for areas that have sedimentary rocks that date to that time period.” 

Caves are significant destinations in surveying and discovering prehistoric animal fossils.  

“Most caves in Thailand are made up of limestone that is 300-250 million years old, but the sediments that fill the caves are approximately hundreds of thousands of years old, making them younger than the caves themselves. Suppose the rock we step on is 300 million years old—geological processes would take more than 100 million years to create the caves we see today, such as the uplift of the earth’s surface, mountain formation, or underground water erosion creating caverns. Once the cave becomes a hollow space, surrounding sediments flow in to fill the cave’s cracks.” 

“To find terrestrial mammals, we need to search along cave fractures where sediments from around the cave have filled in. Later, these sediments harden from calcium carbonate solutions or rainwater that dissolves limestone and coats them. For example, if an animal died near a cave, the remains would decompose, and then rain would wash the decomposed remains into crevices or cavities inside the cave along with the surrounding cave sediments,” explained Assoc. Prof. Dr. Kantapon.

Determining Fossil Age through Scientific Methods

Cave sediments allow for a rough estimation that the spotted hyena fossils found in caves are several hundred thousand years old. However, this may not be the exact age, said Assoc. Prof. Dr. Kantapon, because the animals may have died long before being buried in cave sediments, creating limitations in determining the precise age. Therefore, various scientific methods must be used in combination for analysis. Currently, there are 3 main methods:

1. Direct tooth age determination using Electron Spin Resonance principles 
2. Sediment age determination using Optically Stimulated Luminescence principles, or determining the age of sediments last exposed to light 
3. Rock age determination using U-Series principles to analyze the age of speleothems (stalactites and stalagmites) that accumulated and covered the sediment layers where fossils were found 

“Thailand has the equipment for all 3 methods, but we don’t have direct expertise in determining the age of fossils and cave sediments. Therefore, I had to rely on cooperation from foreign experts and brought Australian and Spanish specialists to collect soil sediment samples where hyenas were found. We took the soil and tooth fragments for analysis and learned that the hyena fossils found are approximately 200,000 years old and date back to the Pleistocene epoch, or Ice Age.” 

Ice-Age Spotted Hyenas in Thailand 

Assoc. Prof. Dr. Kantapon said that the spotted hyena fossils found at Khao Yai Ruak Cave and Khao Toh Luang Cave are likely the same species. At Khao Yai Ruak Cave, a jawbone with 3 consecutive teeth was found still in perfect condition from when the animal died, even though more than 200,000 years have passed. 

“Spotted hyenas belong to the mammal group and are carnivores. Their teeth have sharp pointed cusps. Carnivores have unequal numbers of teeth, and their dental sets are divided into several types such as incisors, canines, molars, and premolars. The upper premolars of spotted hyenas have a blade-like appearance, which is distinctive and larger than those of typical wolves today,” added Assoc. Prof. Dr. Kantapon.

The analysis of the hyena tooth fossils found in Khao Yai Ruak Cave for isotope ratios, along with physical component analysis, conducted in Germany, not only indicates that hyenas lived in savannas but also tells us what they ate. 

“The carbon isotope values from the hyena teeth match those of wild deer, which are herbivores. So, we know that hyenas likely ate wild deer as food, because when they consumed deer, the carbon isotope values from the wild deer entered into the tooth formation process of the spotted hyenas. The carbon isotope values from wild deer also indicate they ate grass, which shows that in the past, the southern region during the Ice Age was likely filled with grasslands.” 

Assoc. Prof. Dr. Kantapon is interested in studying life forms during the Ice Age, or Pleistocene epoch (approximately 2.6 million years–12,500years ago), which was the period before the Holocene epoch, or the current warm period. 

“I’m interested in studying what life forms looked like during the Ice Age and found that this era had spotted hyenas and orangutans. But when the world was in warm periods between ice ages, we found tiger fossils and many other animal species similar to animals in the current era.” 

Fossils from different time periods reveal changes in the environment and climate that affected the existence of living organisms, elaborated Assoc. Prof. Dr. Kantapon.

“When the world became warmer and more humid, tall trees were able to grow higher, causing difficulty for grasslands to flourish. Hyenas did not like this environment, as they were not adept at hunting in dense woodlands, so they gradually became extinct from the area that is currently Thailand.” 

Grasslands and Mixed Forests During the Ice Age  

From “The Survey of Pleistocene Mammalian Fossils in Southern Thailand” research, Assoc. Prof. Dr. Kantapon also discovered that Thailand during the Ice Age was not merely savanna grasslands but also had areas of mixed forests. 

“Thailand is located in an area influenced by monsoon winds. Its humid weather conditions are consistent with the formation of rainforests due to the influence of monsoon winds blowing from the sea. However, some areas were not directly affected by ocean monsoons or may have received monsoon winds that brought drought. Grasslands could then develop extensively in those areas. From my fossil studies, there were many mammals that lived in grasslands, but there were still remaining forest areas that were once habitats for orangutans, which have since gone extinct in Thailand.” 

Assoc. Prof. Dr. Kantapon added that fossils of ice-age orangutans were found in Thailand, first in Chaiyaphum, before more discoveries occurred in the caves in the North and then the South.

“This is evidence that orangutans dispersed from China to Indonesia during the Ice Age, with Thailand serving as a corridor. Pleistocene orangutans have carbon isotope values that we analyzed matching the carbon isotope values of their current populations living in trees, showing that during the time when savanna grasslands existed, forests were also present. “Likely they were open forests, not pure savanna grasslands like those found in Africa,” explained Assoc. Prof. Dr. Kantapon about discoveries from fossil surveys in caves in Krabi over the past 5 years. Currently, orangutan tooth fossils are undergoing research studies for species identification. 

Corridor for Homo Erectus  

Not only orangutans, but southern Thailand was also a dispersal route for ancient humans like Homo erectus, who traveled from Africa and appeared in Indonesia. 

“Homo erectus was an ancient human species that emerged approximately 2,000,000 years ago in Africa and went extinct around 100,000 years ago in Indonesia, as no Homo erectus remains have been found after that period, with Homo sapiens replacing them.” 

In addition to prehistoric mammalian fossils, Assoc. Prof. Dr. Kantapon has been trying to identify fossil evidence of Homo erectus from the Pleistocene epoch in Thailand. For over 7 years, he has conducted research on “The Study of Paleoenvironments Where Ancient Humans Lived During the Pleistocene in the Thai Peninsula,” hypothesizing that “Thailand was a dispersal corridor for Homo erectus connecting South Asia to the Indonesian archipelago, because if ancient humans were able to travel to the Indonesian islands during periods when sea levels dropped and the Sunda continental shelf became land, Thailand would serve as a geographical connecting route.” 

“All ancient human species of the genus Homo originated in Africa, until the environment in Africa began changing from forests to savannas, which facilitated migration out of the continent. From geological evidence and fossils in the Southeast Asian region, it’s believable that most of Thailand’s area during the Ice Age was savanna grasslands.” 

“The hypothesis supporting human migration from the Southeast Asian mainland to the Java islands is called the ‘Savannah Corridor hypothesis,’ which was proposed over 30 years ago, because if the landscape was mostly covered by rainforests, it might not be conducive to the dispersal of ancient humans.” 

“Scientists are currently trying to find paleoclimatic evidence, such as palynological evidence and various isotope analyses, and the latest research suggests that the Sunda continental shelf area or the Gulf of Thailand region that was once a land bridge, may have consisted more of open forests rather than grasslands. Nevertheless, Homo erectus could still cross Sundaland and travel to Java during the Ice Age.” 

In addition to savannas, lower sea levels during the Ice Age were another factor that created more exposed land than today, serving as bridges connecting the mainland with various islands in this region. 

“During the Ice Age, the world had a colder climate than today. Global sea levels dropped, and the Gulf of Thailand became dry land, so Homo erectus used this route to walk through to Indonesia.” 

Certainly there’s a possibility that Homo erectus once lived in the land area of the Gulf of Thailand at that time. “But we still haven’t found fossil evidence, and of course it’s difficult to survey for fossils in the sea,” said Assoc. Prof. Dr. Kantapon.

The Return of the Ice Age  

From studying prehistoric animal remains from the Ice Age, Assoc. Prof. Dr. Kantapon predicts that “the world is moving back towards an ice age.” 

“This is nature’s cycle. Ice ages alternate with warm interglacial periods, occurring throughout the Pleistocene epoch, and there will be alternation between these 2 epochs approximately every 20,000 – 30,000 years. Currently, or in the Holocene epoch, Thailand is in a warm interglacial period. We will certainly enter an ice age next, but while we’re living during this transition to an ice age, the world experiences minor climate variations, including the global warming we’re experiencing today.” 

If Homo sapiens or modern humans survive the global warming crisis and maintain the species for another ten thousand years until the world enters an ice age, what will happen then? 

“10,000 years from now, no one can know for certain what will happen. If technology continues to develop, we may be able to establish settlements in space by then. Natural disasters may not be the main factor destroying humanity. However, the current trend we know well is that the collapse of ecosystems, one linked to food, water, and resources, all of which are the main factors for our survival, has already begun. Hunting, habitat encroachment, and climate change have caused animals to go extinct at very high rates from the Industrial Revolution period until the present.” 

Assoc. Prof. Dr. Kantapon added that studying Ice Age animals and understanding the environment of that era allows for the recognition of the importance of biodiversity in the past and to plan the restoration of habitats and environments suitable for the survival of living organisms today. This will directly impact the conservation of species that are on the verge of extinction in the near future, based on evidence from the past, namely the fossil record itself. 

Chulalongkorn University’s Geological Museum, Department of Geology, Faculty of Science, Chulalongkorn University, is open to the public on Monday–Friday from 8:00 to 16:00 hrs. (closed on public holidays) free of charge.

Reference: https://www.chula.ac.th/news/231429/ 

• Facebook
• Twitter
• Line