A pair of fossil teeth recovered from a coal mine in southern Thailand has revealed a previously unknown giant rodent that lived roughly 33 million to 35 million years ago. The animal, named Yakamys sirindhornae, is estimated to have weighed about 30 kilograms, making it one of the largest rodents known from the Paleogene period.
The discovery is based on an incisor and a lower molar found in 2004 in the Krabi basin. Although the fossils were collected more than two decades ago, researchers from Thailand, France and Canada were only later able to identify their significance through detailed analysis. Their findings were published in Scientific Reports.
Two teeth, a new species
The fossils are modest in number but striking in scale. Pannipa Tian, a geologist with Thailand’s Department of Mineral Resources who found the incisor, initially thought the unusually large specimen was a bone. A second team member found the molar on the same day.
The analysis concluded that the teeth belonged to a new genus and species, Yakamys sirindhornae. The fossil animal has been described as a “giant rat,” though it was not a close equivalent of the familiar rats that live today. It belonged to Ischyromyidae, an extinct family among the earliest major rodent groups.
The estimated body mass of about 30 kilograms places the animal well beyond the size of ordinary modern rodents. It was still smaller than a large capybara, the largest living rodent, but its size is notable for an animal living in the Paleogene, a period that followed the extinction of non-avian dinosaurs and saw mammals diversify into new ecological roles.
A window into ancient Southeast Asian ecosystems
The Krabi basin has already produced fossils of ancient primates, carnivores and hoofed mammals. The addition of a very large rodent broadens the picture of the communities that occupied what is now southern Thailand during the early Cenozoic era.
Large body size is particularly useful to researchers studying rodent evolution because rodents are now a remarkably diverse mammal group, yet much of their early history is preserved in fragmentary fossils. Teeth are often among the most durable and informative remains: their shape, ridges and enamel patterns can distinguish lineages even when skulls and skeletons are absent.
The Thai fossils also raise questions about geography. One member of the research team suggested that ancient rodents may have evolved in the region before spreading elsewhere. The current evidence does not settle that history, but it adds a significant data point from Southeast Asia, a region whose fossil record can help test ideas built largely from finds in other parts of the world.
Important limits on what the fossils can show
The new species is known from only two teeth. That makes it possible to identify a distinct rodent lineage and estimate its size, but not to reconstruct its full appearance or way of life with confidence. Researchers do not yet know its diet, behavior or the details of its habitat.
Those unanswered questions are part of the value of the find. A single fossil site can preserve evidence of lineages that have no living descendants, while also pointing to gaps that further fieldwork may fill. More remains from the Krabi basin could reveal whether Yakamys was a specialized browser, a generalist feeder or part of a wider assemblage of oversized mammals.
Why the discovery matters
Fossil discoveries are not only about identifying spectacular extinct animals. They also help researchers map how body size, ecology and geographic distribution changed as mammals diversified. In this case, two teeth have documented a large, extinct rodent lineage in Thailand and extended the known diversity of Paleogene mammals in the region.
Yakamys sirindhornae lived about 33 million to 35 million years ago.
It is estimated to have weighed around 30 kilograms.
The species was identified from an incisor and a molar found in southern Thailand.
Its closest broad grouping is the extinct Ischyromyidae family.
The evidence is limited, but it is enough to establish that giant rodents were part of ancient Southeast Asian ecosystems. Future fossils may turn this isolated dental record into a fuller account of an animal that, for now, is known mainly through the unusually large teeth it left behind.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
