Late Pleistocene gray whales (Eschrichtius robustus) offshore Georgia, U.S.A., and the antiquity of gray whale migration in the North Atlantic Ocean

•Documentation of Pleistocene sub fossil remains of Atlantic gray whales•Record of the oldest gray whales from the North Atlantic basin•Morphological measurements of sub fossils diagnostic to gray whale•Support that Georgia coast was winter breeding ground for extinct gray whales•Paleoecology of large cetaceans

Living gray whales (Eschrichtius robustus) are key consumers in benthic communities of the North Pacific Ocean. Gray whales, however, also inhabited the North Atlantic Ocean until recent historical times (~ 1600 AD), leaving open questions about their historical ecology in nearshore communities of this basin. Here we report the discovery of fossil remains from two individual gray whales recovered from underwater excavations at separate localities of JY Reef, an offshore reef situated approximately 32 kilometers (km) offshore of St. Catherine's Island, Georgia, U.S.A. Both mandibles are diagnostic to the living E. robustus. Radiometric dating of shells from JY Reef suggests an approximate age range of these two specimens between 42 and 30 thousand years before present (ka). Morphological measurements of the preserved elements indicate that both of the mandibles likely belonged to immature and possibly yearling individuals. Collectively, these findings are among the oldest occurrences of gray whales in the North Atlantic basin, and their presence at temperate latitudes provides limited support for the hypothesis that Atlantic gray whales used a southerly breeding area at the end of a migratory pathway, by analog with lagoonal breeding environments of Baja California, Mexico, for the extant California gray whales, and the breeding areas for the extant North Atlantic right whales (Eubalaena glacialis) off the Georgia coast today. Stronger support for this latter contention may stem from future fossil discoveries in the region, as well as ancillary lines of evidence, such as the remains of species-specific ectoparasites and/or ancient DNA (aDNA).