Research led by Museum scientists shows that ammonites made homes in the unique environments surrounding methane seeps in the seaway that once covered America’s Great Plains. The findings, recently published in the journal Geology, provide new insights into the mode of life and habitat of these ancient animals.
In the Black Hills region of South Dakota, researchers are investigating a 74-million-year-old mound of fossilized material where methane-rich fluids once migrated through the sediments onto the sea floor. When the face of this cliff recently slumped off, a wide variety of bivalves, sponges, corals, fish, crinoids, and, as recently documented, ammonites, were revealed.
Studying these well-preserved shells, the researchers tried to determine the role of ammonites in the unique seep ecosystem. By analyzing the abundance of isotopes (alternative forms) of carbon, oxygen, and strontium, the group made a surprising discovery. The ammonites at the seep, once thought to be transient, had spent their whole lives there. The seeps also likely attracted large clusters of plankton, the ammonites’ preferred prey.