An international team of paleontologists has identified a previously unknown species of giant rodent from fossil remains discovered in a mine in southern Thailand. The species, named Yakamys sirindhornae, lived approximately 34 million years ago during the middle of the Paleogene period. The researchers recovered two teeth—a lower second molar and a lower incisor—from the Bang Mark Pit at the Krabi lignite mine in Thailand’s Krabi Province.
Using seven established methods that rely on tooth measurements to estimate body mass, the research team calculated that Yakamys sirindhornae weighed around 30 kilograms, or approximately 66 pounds. This would have made it roughly twice as heavy as other known rodents from the same era, including a species called Hulgana. However, scientists acknowledge that determining an extinct animal’s weight from limited fossilized teeth involves significant uncertainty. Virginie Millien, a biology professor at McGill University and co-author of the study, emphasized that the figure represents a rough estimate rather than a precise measurement.
The discovery provides evidence that giant rodents appeared much earlier and across more geographic regions than previously understood. While the largest living rodent today is the capybara, and giant rodents are known to have evolved repeatedly later in the group’s history—particularly in South America—this finding indicates that Southeast Asia also played an important role in the early evolutionary development of large-bodied rodents. The species name sirindhornae honors Princess Maha Chakri Sirindhorn in recognition of her support for scientific research in Thailand.
The fossil analysis was conducted through an ongoing international collaboration investigating ancient mammals in Thailand’s Krabi Basin, involving researchers from McGill University, Thailand’s Department of Mineral Resources, and French institutions including CNRS and Université de Poitiers. Scientists note that additional fossil discoveries will be necessary to better understand the species’ physical characteristics, ecological role, and evolutionary relationships to other rodents.
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