Paleontologists have discovered fossils of a giant prehistoric rodent in southern Thailand, providing new evidence that large-bodied rodents evolved earlier and across a wider geographical area than previously understood.
The newly identified species, named Yakamys sirindhornae, lived approximately 34 million years ago. Researchers estimate that it weighed around 30 kilograms, making it roughly twice as large as other known rodents from the same period.
The discovery was made at the Bang Mark Pit of the Krabi lignite mine in Krabi Province by an international research team involving scientists from McGill University, Thailand’s Department of Mineral Resources, and French research institutions.
The findings were published in the journal Scientific Reports.
Giant Rodent Fossils Reveal Southeast Asia’s Evolutionary Significance
The researchers identified fossilised teeth, including a lower second molar and a lower incisor, belonging to the previously unknown species.
The discovery offers new insights into the evolution of rodent gigantism, the process through which rodents develop significantly larger body sizes.
Although giant rodents are commonly associated with South America’s evolutionary history, the findings suggest that Southeast Asia also played an important role in the early development of large-bodied species.
“Today, the largest living rodent is the capybara, but very large rodents are not restricted to recent ecosystems,” said Virginie Millien, study co-author and Professor of Biology at McGill University.
“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.”
The researchers named the new genus Yakamys by combining the Thai word “yak”, meaning giant, with the Greek word “mys”, meaning mouse or rat.
The species name sirindhornae honours Princess Maha Chakri Sirindhorn in recognition of her longstanding support for scientific and paleontological research in Thailand.
Prehistoric Species May Have Weighed Around 30 Kilograms
To estimate the animal’s body mass, the research team applied seven established methods based on measurements of fossilised teeth.
Their calculations suggest that Yakamys sirindhornae weighed approximately 30 kilograms. This would make it about twice the size of other known rodents from the same geological period, including Hulgana.
However, the researchers cautioned that the estimate carries considerable uncertainty because it is based on limited fossil material.
“This is only a ballpark figure, as there is substantial uncertainty associated with fossil body-mass estimation,” Millien said.
Despite these limitations, the estimated size indicates that unusually large rodents existed in Southeast Asia much earlier than previously recognised.
Further Fossil Discoveries Needed to Understand Its Evolution
The discovery emerged from a collaborative research project investigating fossil mammals in Thailand’s Krabi Basin. The initiative involves McGill University, the Department of Mineral Resources of Thailand, and French institutions including the French National Centre for Scientific Research (CNRS) and Université de Poitiers.
Although the fossilised teeth have helped researchers identify the species and estimate its size, the limited remains make it difficult to reconstruct its complete anatomy, biology, and ecological role.
Further fossil discoveries will be necessary to establish how Yakamys sirindhornae evolved and how it relates to other prehistoric rodent groups.
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