A giant rodent weighing about 66 pounds roamed what is now southern Thailand 33 to 35 million years ago, scientists say after identifying a previously unknown species from two fossilized teeth.
The ancient animal, dubbed a “giant rat” by one of the geologists on the research team, is one of the largest animals known from the Paleogene period and provides new clues about how early rodents evolved to their gigantic sizes.
The findings, published Wednesday in the journal Scientific Reports, are based on a molar and an incisor discovered in 2004 in a coal mine in southern Krabi province.
Pannipa Tian, a geologist at Thailand’s Ministry of Mineral Resources who discovered the incisor, said she initially misidentified the fossil because it was “unusually large in size.”
“At first, I thought it was a bone. I showed it to my supervisor and he told me it was a giant rat tooth,” Pannipa, 51, told AFP on Thursday.
The cream-colored fossil stands out against dark coal deposits, the same day another expedition member discovered dark molars.
The Krabi Basin has previously yielded fossils of ancient primates, carnivores and ungulate mammals.
But at the time of discovery, the team lacked sufficient evidence and technology to identify the species.
More than two decades later, researchers from Thailand, France and Canada were able to do just that through detailed analysis of the teeth.
They said the animal weighed about 30 kilograms, estimated to be half the size of the giant capybara, the world’s largest living rodent.
However, unlike the South American capybara, this prehistoric rodent belonged to the now-extinct family Ischyromyidae, one of the earliest major rodents.
“It tells a lot about the diversity of life in the past,” said Pannipa, who believes the ancient rodents may have evolved in what is now Thailand and then spread to other parts of the world.
But with only two teeth recovered, the animal’s appearance, diet and behavior remain unknown.
The species was named Yakamys Sirindhornae in honor of Princess Sirindhorn of Thailand, a supporter of scientific and paleontological research.
While the new species appears large, other discoveries around the world have revealed even larger rodents. In 2020, scientists announced the discovery of a prehistoric human-sized rat that lived in the Amazon rainforest 10 million years ago.
In 2008, Uruguayan scientists said they had discovered fossil evidence largest rodent species A 1-ton creature discovered so far roamed the forested areas of South America some 4 million years ago.
In 2003, researchers said they found fossils weighing 1,545 pounds “Rat pull” Thriving in the swamp forests of South America millions of years ago.