The almost complete skull of a walrus has been discovered in Champlain Sea sediments at Sainte-Julienne-de-Montcalm, 60 km north of Montréal. It is the first report of that species in glacial marine deposits west of Québec City. The skull has been dated by accelerator mass spectrometry at 10 090 ± 60 BP (TO-2224) and the shells in the sediment adhering to it at 10 880 ± 60 BP (TO-2225). The discrepancy between the two age determinations is attributed to diachronism between the skull and the shells, the latter having been redeposited. The radiometric age implies that walruses were part of a Champlain Sea marine vertebrate fauna consisting of three species of seals and five whale species. As the sea drained, walruses withdrew toward the Gulf of St. Lawrence, where they have been hunted to extinction in historic times.