Jaeger, who has announced past discoveries of primate fossils in Thailand, is working with Yaowalak on the latest excavation.
The scientists have not yet established the exact age of the fossils, but they estimate the remains are about 400,000 years old.
"Most are [from] extinct animals in Thailand today," Jaeger said.
Southward Migration
The location where the bones were found used to be a river, and researchers believe the area was once a tropical forest that attracted animals from the north.
"During the cold periods of the Middle Pleistocene era [1.8 million years ago to 11,500 years ago], mammalian communities shifted southwards in Asia in a similar way to Europe and North America," Jaeger said.
As the climate changed and the forested area turned into floodplains, the animal species may have gone extinct.
"This site serves as a link between the past and the present," Yaowalak said.
Studying what happened to the mammals found in the ancient riverbed, she said, could help researchers understand migration patterns for prehistoric animals and early humans.
Scientists believe that, similar to the southward migration of mammals such as the stegodon, populations of Homo erectus may also have moved south in Asia at one point.
Researchers have been focusing on cave deposits as they look for remains of Homo erectus in Thailand. The latest discovery, however, suggests they may have to broaden their search.
"We didn't expect to find these [mammal] remains in a river deposit," Yaowalak said. "Maybe now we will change our mind as to where to look for human ancestors."
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