Scientists identified a previously unknown species of giant rodent that lived in present-day southern Thailand approximately 33 to 35 million years ago. The discovery, based on two fossilized teeth, reveals a creature estimated to weigh around 30 kilograms (66 pounds), making it one of the largest known rodents from the Paleogene period.
The fossils, consisting of a molar and an incisor, were originally discovered in 2004 at a coal mine in the Krabi province of southern Thailand. Pannipa Tian, a geologist with Thailand’s Department of Mineral Resources, reported that she initially misidentified the incisor due to its large size before her supervisor identified it as a rodent tooth. While the Krabi basin has yielded fossils of primates and carnivores in the past, researchers lacked the technology and evidence to identify this specific species at the time of the find.
After two decades, a joint team of researchers from Thailand, France, and Canada analyzed the teeth to confirm the new species. They named the animal Yakamys sirindhornae in honor of Thailand’s Princess Sirindhorn. According to the research team, the rodent belonged to the extinct Ischyromyidae family, which was one of the first major groups of rodents, rather than the lineage of the modern capybara.
For the general public, the discovery clarifies the prehistoric biodiversity of Thailand. The scale of the animal—roughly half the weight of a modern capybara—highlights a period of mammalian growth millions of years ago. However, because only two teeth were recovered, scientists noted that specific details about the animal's physical appearance, diet, or social behavior cannot yet be determined.
The research establishes Yakamys sirindhornae alongside other large prehistoric rodents found in South America, such as the 1-ton species reported in Uruguay in 2008 and the 1,545-pound creature identified in 2003. What happens next involves ongoing analysis of the Krabi basin deposits. The findings were published in the journal Scientific Reports on a Wednesday, providing a peer-reviewed foundation for future paleontological expeditions in Thailand. Further discoveries would be required to determine the full skeletal structure of the species.