Four bivalve specimens from Antarctica’s Seymour Island analyzed in the University of Michigan-led study, showing the range of sizes of the different mollusks. Species names clockwise from the top shell: Lahillia larseni, Cucullaea antarctica, Eselaevitrigonia regina and Cucullaea ellioti. Photo credit: Sierra V. Petersen.

Two small drill holes below a larger drilled area show where sample material was extracted from the umbo (hinge) region of this Cucullaea antarctica shell, with four other shells of the same species in the background. Photo credit: Sierra V. Petersen.

In some specimens, the two halves of the bivalve were still connected as in life, as in this small Cucullaea antarctica specimen. The mollusks analyzed in the U-M-led study lived 69 to 65.5 million years ago in a shallow coastal delta near the northern tip of the Antarctic Peninsula. Photo credit: Sierra V. Petersen.

The preservation of Cretaceous mollusk fossils from Seymour Island is excellent, with shells preserving original mother-of-pearl material as in these two specimens of Eselaevitrigonia regina. Photo credit: Sierra V. Petersen.