Mongolian Microfossils Point to the Rise of Animals on Earth

The new cache of fossils represents eight genera and about 17 species, comprising tens to hundreds of individuals. Many of them are spiny microfossils called acritarchs, which are roughly 100 microns in size — about one-third the thickness of a fingernail.

The Khesen Formation is located to the west of Lake Khuvsgul in northern Mongolia. “This site was of particular interest to us because it had the right type of rocks — phosphorites — that had preserved similar organisms in China,” Anderson said.

The discovery may help scientists confirm a much earlier date for the existence of Earth ecosystems with animals, rather than just microbes. For two decades, researchers have debated the findings at the Doushantuo Formation, with no resolution. If confirmed as animals, these microfossils would represent the oldest animals to be preserved in the geological record.

The other authors of the study are Derek Briggs, Yale’s G. Evelyn Hutchinson Professor of Geology and Geophysics and curator at the Yale Peabody Museum of Natural History; Sean McMahon, a postdoctoral fellow in the Briggs lab; Francis Macdonald of Harvard; and David Jones of Amherst College.

The researchers said the Khesen Formation should provide scientists with additional information for years to come.

“This study is only the tip of the iceberg, as most of the fossils derive from only two samples,” Anderson said. Since the original discovery, the Yale team has worked with Harvard and the Mongolian University of Science and Technology to sample several additional sites within the formation.