Scientists Identify Giant 66 Pound Rodent in Thailand

Fossilized teeth have revealed a previously unknown giant rodent that weighed approximately 66 pounds and lived in what is now southern Thailand between 33 and 35 million years ago. Researchers identified the extinct species from two teeth discovered in a coal mine in Krabi province, placing it among the largest known rodents of the Paleogene period.

The findings, published Wednesday in the journal Scientific Reports, identify the species as Yakamys sirindhornae. Its estimated weight was approximately 30 kilograms, about half the weight of a large capybara, the world's largest living rodent, according to the research team.

The fossils consist of a molar and an incisor recovered in 2004. Researchers from Thailand, France and Canada eventually identified the animal through detailed examinations of the specimens more than two decades after their discovery.

Pannipa Tian, a geologist with Thailand's Department of Mineral Resources, discovered the incisor during the expedition. Its unusual dimensions initially led her to mistake it for another type of fossil.

"At first, I thought it was a bone. I showed it to my supervisor, who told me it was a giant rat's tooth," Pannipa, 51, told AFP on Thursday.

The cream-colored incisor was particularly noticeable against the mine's dark coal deposits. Another expedition member discovered the darker molar on the same day.

The Krabi Basin had previously produced fossils of ancient primates, carnivores and hoofed mammals. However, the researchers initially lacked the evidence and technology needed to establish the identity of the animal represented by the teeth.

The newly identified species belongs to the extinct Ischyromyidae family, one of the earliest major groups of rodents. This distinguishes it from the modern capybara, which belongs to a different evolutionary lineage.

Pannipa said the discovery highlights the variety of animals that inhabited the region millions of years ago.

"It tells a lot about the diversity of life in the past," Pannipa said, suggesting that ancient rodents may have evolved in what is now Thailand before spreading to other parts of the world.

Despite the identification, scientists have limited information about the animal's physical appearance, diet and behavior because only two teeth have been recovered. The species received the name Yakamys sirindhornae in honor of Thailand's Princess Sirindhorn, who supports scientific and paleontological research.

Other fossil discoveries have documented rodents considerably larger than the newly identified Thai species. In 2020, scientists announced the discovery of a prehistoric rodent roughly the size of a human that inhabited the Amazon rainforest approximately 10 million years ago.

Uruguayan scientists also reported fossil evidence in 2008 of a rodent weighing approximately one ton. The animal lived in wooded areas of South America around 4 million years ago.

Another discovery announced in 2003 involved fossils attributed to a 1,545-pound rodent that inhabited a swampy South American forest millions of years ago.