Phoebe Cohen's Research Published in Two Journals

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WILLIAMSTOWN, Mass., June 28, 2017—Phoebe Cohen, assistant professor of geosciences at Williams College, has published her most recent research that dates shell-making in fossils to a time 200 million years earlier than originally thought. The research was published this week in Science Advances. Additionally, Cohen’s research with Spencer Irvine ’16 on vase-shaped microfossils (VSMs) was published this week in the journal Palaeontology.

In Science Advances, Cohen details her research into fossilized eukaryotes, which are complex life-forms that include plants and animals but also a wide diversity of single-celled organisms. These single-celled eukaryotes were discovered in Canada and show layers of mineral plates. At more than 800 million years old, they represent the oldest evidence of organisms controlling the formation of minerals, known as biomineralization.

These ancient life-forms built their exoskeletons using a different process than modern shell-making eukaryotes, Cohen said, adding this research shows how mineral-making evolved. Previous evidence dated biomineralization to 560 million years ago.

“The most important thing from this research is that eukaryotes were building very complex biomineralized structures much earlier than we thought they were, and that they were using minerals that were available to them at the time—even if they don’t often use those minerals today,” Cohen said. “What’s powerful to me is the co-evolution story—organisms and their environment evolved together through time. I think this is important because it leads to some interesting questions about why and how organisms biomineralize. This is really intriguing and something we’ll be following up with in the future. Sometimes the most important part of a discovery can be that it leads to questions you didn’t even know to ask and that can lead to new ideas.”

Cohen and colleagues dated the organic-rich shale a few meters below the fossils, and pegged the fossils’ age at 809 million years old, give or take a few million years. An electron microscope let researchers see that each plate is woven out of elongated mineral fibers. This intricate, orderly design had to have been purposefully built by life manipulating mineral formation, Cohen said.

In Palaeontology, Cohen and Irvine, along with Dartmouth College researcher

Justin Strauss, take a look at the abundance, taxonomy and taphonomy of VSMs from the Callison Lake Formation in Yukon, Canada.

VSMs, which are interpreted as the remains of testate amoebae, are found in Late Tonian sedimentary rocks around the world. A new assemblage of them recently was described in the Callison Lake Formation in Yukon, Canada. Found in silicified black shale horizons, as well as carbonate rocks, data suggests these VSMs inhabited a lagoonal or shelf interior environment. These microfossils are indicative of early diversification of eukaryotic life.

The team’s work also uncovered two new species of VSMs—a long-necked form and an elongate, curved-neck form.

Professor Justin Strauss from Dartmouth first described this set of fossils, and the work by Cohen, Irvine and Strauss carried on the research into them. Irvine wrote his senior thesis about the research, which formed the basis of the paper submitted to Palaeontology.


Founded in 1793, Williams College is the second-oldest institution of higher learning in Massachusetts. The college’s 2,000 students are taught by a faculty noted for the quality of their teaching and research, and the achievement of academic goals includes active participation of students with faculty in their research. Students’ educational experience is enriched by the residential campus environment in Williamstown, Mass., which provides a host of opportunities for interaction with one another and with faculty beyond the classroom. Admission decisions on U.S. applicants are made regardless of a student’s financial ability, and the college provides grants and other assistance to meet the demonstrated needs of all who are admitted.