Fossil teeth place Yakamys among the giant rodents of Eocene Thailand
Fossil teeth from southern Thailand identify Yakamys sirindhornae, a newly described rodent that lived roughly 35 million years ago. Dental comparisons suggest a body mass around 30 kilograms, with substantial uncertainty. The peer-reviewed discovery places exceptionally large rodents in an early Asian lineage, well before the better-known giant rodents of South America’s Neogene period.
Science··Evening
Teeth reveal an ancient giant
Researchers have identified Yakamys sirindhornae, a previously unknown giant rodent, from teeth recovered in southern Thailand. The animal lived in the Krabi Basin roughly 35 million years ago. Its description, published after peer review on 4 November, adds an Asian example to the early history of exceptionally large rodents. Dental estimates place its mass at around 30 kilograms, although considerable uncertainty surrounds that figure.[1], [2]
The specimens came from a clay layer at Bang Mark, a lignite mine in Thailand’s Krabi region. The clay accumulated in a lake environment during the late Eocene, approximately 35.1–33.7 million years ago. A lower second molar supplies the main anatomical evidence. A nearby incisor was provisionally assigned to the same species because its size and location were compatible.[1]
Body size comes from dental comparisons
The molar is 11.56 millimetres long and 11.27 millimetres wide, with a crown reaching 7.85 millimetres in height. Its shape and the organization of enamel in the incisor support placement in Ischyromyidae, an early family of rodents. Three-dimensional tooth images and enamel sections provided the anatomical comparisons used to distinguish the new species. The fossils are kept in the collection of Thailand’s Department of Mineral Resources.[1]
Gigantism predates the familiar South American examples
Comparative equations relating tooth dimensions to body mass gave central estimates between 21.4 and 47.3 kilograms. Their mean was 31.6 kilograms and their median 28.6 kilograms. These are estimates from teeth rather than a skeleton with preserved body dimensions; model prediction errors widen the possible range further. The rounded description of about 30 kilograms summarizes that calculation rather than an exact weight.[1]
The rodent Yakamys documents substantial body-size growth in an early Asian rodent lineage before the Neogene giants better known from South America. Large size arose repeatedly among rodents, across different evolutionary histories. The small fossil sample leaves this species’ detailed ancestry unresolved. Lake sediments also leave its way of life open: they do not establish that it spent time swimming or that island isolation drove its size.[1]
