An Ancient Animal Assembly
In the sediments of central Myanmar, paleontologists have uncovered a large collection of mammal fossils dating to the Miocene Epoch, approximately 23 to 5.3 million years ago. These remains are primarily found within the Irrawaddy Formation, a thick layer of river-deposited sandstones and clays that is also characterized by abundant silicified fossil wood. The specific fossil-bearing layers near Pyinmana are considered to be from the late Miocene, around 11 to 5 million years ago.
The animal life of this period was remarkably diverse. Among the most significant finds are the ancestors of modern elephants, known as proboscideans. Species like Stegolophodon and members of the Gomphotheriidae family roamed this ancient region. Alongside these giants were several species of rhinoceros. One common genus was Brachypotherium, a large, hornless rhinoceros that was widespread across the Old World during the Miocene. The fauna also included ancient pigs like Tetraconodon and Propotamochoerus, early horse relatives called Hipparion, and various bovids (the family that includes cattle and antelope) and giraffids. The discovery of a hominoid primate, Khoratpithecus ayeyarwadyensis, shows the range of mammals present in this ecosystem.
Reading the Tooth Record
The teeth of these fossilized animals provide direct evidence of their diet and the environment they inhabited. Through a method called dental microwear analysis, scientists study the microscopic scratches and pits on the enamel surface. Different foods leave distinct patterns. Tough grasses, which contain abrasive silica particles, create fine, parallel scratches, a pattern typical of grazers. Softer foods like leaves and fruit result in fewer scratches and more pits, the signature of a browsing animal.
Analysis of tooth enamel from the Irrawaddy Formation fauna, including bovids and hippopotamids, shows patterns consistent with a diet of C4 plants—grasses adapted to open, sunny environments. This dental evidence strongly suggests that the region was not the dense forest it is today, but a more open C3/C4 grassland or savanna ecosystem. The presence of woodland-adapted animals alongside grazers points to a mosaic environment with forests near riverine areas and extensive grasslands beyond.
This ancient savanna is different from the modern landscape. The environmental shift is believed to be linked to long-term geological and climatic changes, including the uplift of the Himalayas, which altered monsoon patterns and eventually favored the development of the forests that now dominate central Myanmar. The fossils of Pyinmana Township record a world when the climate and ecology of Southeast Asia were dramatically different.