Yakamys sirindhornae: giant rat weighing 66 pounds
Scientists identified Yakamys sirindhornae from two fossilized teeth found in southern Thailand. The rodent weighed around 30 kilograms and lived 33 to 35…
Scientists identified Yakamys sirindhornae, a giant rat weighing 66 pounds, from two fossilized teeth found in southern Thailand, revealing a rodent that lived there 33 to 35 million years ago. The animal weighed around 30 kilograms and was among the largest known rodents of the Paleogene period.
The finding links a small fossil record to a much larger question: how early rodents evolved to enormous sizes. Researchers analyzed a molar and an incisor discovered at a coal mine in Krabi province.
The evidence is strikingly limited. Just two teeth.
The findings were published Wednesday in the journal Scientific Reports. Researchers from Thailand, France and Canada identified the previously unknown species through detailed analysis, more than two decades after the fossils were found.
What did the fossilized teeth reveal?
The teeth established that the animal belonged to the extinct Ischyromyidae family, one of the earliest major groups of rodents. The species name, Yakamys sirindhornae, honors Thailand’s Princess Sirindhorn, who supports scientific and paleontological research.
Pannipa Tian, a geologist with Thailand’s Department of Mineral Resources, found the incisor. She said its size initially led her to mistake it for a bone.
“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 said on Thursday.
The fossil was cream-colored and stood out against dark coal deposits. Another member of the expedition found the dark-colored molar on the same day.
The discovery dates to 2004, but the team initially lacked enough evidence and technology to identify the species. The later analysis turned the two isolated teeth into evidence for an animal that adds to scientists’ understanding of rodent diversity in the distant past.
Why does the Thailand discovery matter?
The animal’s estimated weight was around 30 kilograms, roughly half that of a large capybara, the world’s largest living rodent, according to the researchers. But the comparison has limits: the ancient animal belonged to a different, now-extinct family and lived tens of millions of years ago.
Pannipa said the finding “tells a lot about the diversity of life in the past.” She also suggested ancient rodents may have evolved in what is now Thailand before spreading to other parts of the world.
That possibility gives the Krabi fossils significance beyond the size of the animal. They offer a clue to where early rodent groups may have developed, while leaving major parts of the creature’s life unresolved. With only teeth recovered, researchers do not know what it looked like, what it ate or how it behaved.
The Krabi basin had previously yielded fossils of ancient primates, carnivores and hoofed mammals. The newly identified rodent adds another group to the record from the area, but the two teeth remain the only evidence described for this species.
The researchers placed the animal among the largest known from the Paleogene period. Its estimated weight, around 30 kilograms, puts a concrete measure on that claim, even as its body and habits remain out of reach.
