The Late Devonian mass extinction (roughly 372 million years ago) was one of five mass extinctions in Earth’s history, with roughly 75% of all species disappearing over its course. It happened in two ‘pulses,’ spaced about 800,000 years apart, with most of the extinctions happening in the second pulse. However, for one group of animals living in eastern North America, the first pulse dealt the deadlier blow.

Research out today in Scientific Reports looks at how and why this group of animals, called brachiopods, seemed to do the opposite of so many other species. What caused this group to hit the accelerator toward extinction?

Brachiopods are small, shelled, filter-feeding ocean dwellers that are extremely abundant and well-preserved in the fossil record, says researcher Jaleigh Pier ’18 (CLAS), now a Ph.D. student in Earth and Atmospheric Sciences at Cornell University. These qualities make brachiopods ideal for studying disturbances, like mass extinctions, from the deep past.

Pier started this research as a master’s student in the Department of Ecology and Evolutionary Biology in the lab of Professor Andrew Bush, who is a member of EEB and Geosciences. Many samples had been previously collected by others in Bush’s group, including co-author and Ph.D. student Sarah Brisson (Department of Geosciences), who also helped with the identification and classification. The specimens were collected from several sites near the border of New York and Pennsylvania, which, in the Late Devonian, had been a shallow sea.

For this study, Pier identified around 8,000 brachiopod specimens to determine which species were present leading up to this first pulse, while Brisson identified the species that were still around after the extinction. Andrew Beard ’21 Ph.D., with guidance from Professor Michael Hren from the Department of Geosciences, performed geochemical measurements to confirm the timing of the extinction pulses and to determine oxygen levels during the extinctions.

Bush says it was surprising to discover the first pulse was more detrimental to the brachiopods in this area, and they wanted to understand why. To answer this question, Pier says it is necessary to apply a comparative approach.

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Materials provided by University of Connecticut. Original written by Elaina Hancock. Note: Content may be edited for style and length.