35-Million-Year-Old Fossil Teeth from Thailand Reveal Rodent as Heavy as Large Dog

” Today, the biggest living rodent is the capybara, however huge rodents are not limited to current environments, “stated McGill University’s Professor Virginie Millien, co-author of a paper released in the journal Scientific Reports

“Giant rodents developed consistently throughout the later history of the group, mainly in South America.

“Our discovery recommends that Southeast Asia likewise played an essential function in the early evolutionary history of large-bodied rodents.”

In the paper, Professor Millien and associates explained a brand-new rodent types from the Late Eocene, in between about 35 and 34 million years earlier.

Called Yakamys sirindhornaethe animal is understood from simply 2 fossils: a single lower molar and a piece of a lower incisor.

Both were discovered in a clay layer within a coal joint at the Krabi lignite mine in Thailand’s Krabi province.

The molar steps about 11.6 mm long and 11.3 mm broad; the biggest formerly recognized Asian loved ones had molars less than half that size.

The paleontologists approximated that Yakamys sirindhornae weighed approximately 30 kg– about the size of a big pet dog.

“This is just an estimate, as there is significant unpredictability related to fossil body-mass evaluation, “Professor Millien stated.

The scientists put the brand-new types in the Ischyromyidaean early rodent household, based upon its tooth shape and on the tiny structure of its incisor enamel.

Regardless of the incisor’s size, its enamel is extremely thin, about 235 micrometers.

Before this discovery, among the couple of recorded examples of a huge early rodent was Manitsha tankaan ischyromyid from the Oligocene of South Dakota.

The scientists approximate that the 2 animals had likewise big body masses, yet their molars vary considerably fit and size, which recommends that big ischyromyids did not share a single tooth style.

The discover recommends that huge body size progressed in rodents well before the giants of South America, such as Josephoartigasia monesiwhich resided in the Plio-Pleistocene and was approximated at about 350 kg in later research studies.

“Because the fossil product is restricted, it is hard to identify precisely how Yakamys sirindhornae developed,”Professor Millien stated.

“Further discoveries will be very important for comprehending the animal’s biology, ecology and evolutionary history. ”

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Y. Chaimanee et al2026. A huge Eocene ischyromyid from Southeast Asia exposes the early advancement of rodent gigantism. Sci Rep 16, 34523; doi: 10.1038/ s41598-026-76711-6