An international team of paleontologists has identified fossils of a giant 66-pound prehistoric rodent that lived in southern Thailand roughly 34 million years ago. McGill University announced the find on November 10; it was published in Scientific Reports. Researchers named the new species Yakamys sirindhornae after finding two remarkably large fossil teeth—a lower second molar and a lower incisor—at the Bang Mark Pit of the Krabi lignite mine in Krabi Province. The genus name combines the Thai word yak, meaning giant, with the Greek mys, meaning mouse or rat.
Giant rodents evolved repeatedly during the later history of the group, mostly in South America. This discovery suggests that Southeast Asia also played an important role in the early evolutionary history of large-bodied rodents, said McGill University biology professor Virginie Millien. Using seven established formulas that calculate body mass from dental dimensions, the team estimated Yakamys weighed approximately 30 kilograms, or 66 pounds; estimates span 47 to 104 pounds depending on the equation. Even the midpoint makes Yakamys roughly twice the size of other known rodents from the mid-Paleogene period, such as Hulgana. Today, the largest living rodent is South America's capybara, which lives in wetland habitats.
Millien cautioned that estimating weight from limited fossil teeth carries substantial uncertainty. The species name, sirindhornae, honors Princess Maha Chakri Sirindhorn for her longstanding support of science and paleontological research in Thailand. The project united scientists from McGill University, Thailand's Department of Mineral Resources, France's CNRS, Université de Poitiers, and Université de Montpellier. Yaowalak Chaimanee and Laurent Marivaux joined Millien and Thai and French colleagues in authoring the paper. Because only two fossil teeth have been recovered so far, researchers cannot yet reconstruct how Yakamys lived, what it ate, or how it moved.
