Ancient Giant Rodent Species Discovered in Thailand Coal Mine
Fossilized teeth from the late Eocene reveal early rodent gigantism in Southeast Asia.
1Discovery in Krabi Mine
A Thai-French expedition discovered two fossilized teeth within a clay band at the Krabi lignite mine in southern Thailand. These remains, identified as a molar and a lower incisor, belong to a newly named species, Yakamys sirindhornae. The fossils were recovered from a geological layer dating back 35.1 to 33.7 million years.
2Estimating Body Mass
Researchers estimate the rodent weighed approximately 30 kilograms, roughly the size of a large dog. This figure was derived from seven different mathematical equations based on living rodents. However, the team emphasizes this is a loose summary, as the wide range of statistical error spans from 10.8 to 69.0 kilograms total.
3Taxonomic Classification Details
The species is classified within the extinct family Ischyromyidae, a group of very early rodents. Microscopic analysis of the incisor enamel revealed Hunter-Schreger bands, which are sheets of enamel rods that cross each other. This specific structural pattern is a diagnostic feature used to confirm the animal's placement within this ancient family.
4Comparison to Other Giants
Yakamys sirindhornae represents a significant departure from typical Asian ischyromyids, which were generally small. Its molar is more than twice the size of previously known Asian relatives. It shows similarities in mass to Manitsha tanka, an Oligocene rodent from South Dakota, though their tooth shapes differ, indicating diverse evolutionary designs for gigantism.
5Evolutionary Timeline Significance
This discovery suggests that large body sizes in rodents evolved much earlier than the famous giants of South America, such as Josephoartigasia monesi. While South American caviomorphs diversified millions of years later, Yakamys sirindhornae demonstrates that Southeast Asia played a critical, previously unrecognized role in the early history of large-bodied rodent evolution.
6Technical Analysis Methods
To study the specimens, researchers used an EasyTom 150 micro-CT machine for 3D modeling and a Hitachi S-4000 scanning electron microscope for enamel analysis. The molar, measuring 11.56 millimeters long, serves as the holotype. These high-resolution scans are being archived in MorphoMuseuM to allow for open access and further scientific study.
7Naming and Preservation
The name Yakamys combines the Thai word 'yak' for giant and the Greek 'mys' for mouse. The species honors Princess Maha Chakri Sirindhorn for her support of Thai paleontology. The Department of Mineral Resources in Bangkok currently holds the specimens, cataloged as TF 2942 and TF 2943, for future research reference.
8Future Research Directions
Because the current evidence is limited to two teeth, a formal family-tree analysis remains impossible. Scientists hope to find more skeletal material to understand the animal's biology and ecology. An unpublished, large incisor from Myanmar's Pondaung Formation suggests that other unidentified giant rodents may still be waiting to be formally described.
Original article: Earth.com — Ancient Giant Rodent Species Discovered in Thailand Coal Mine