Landman N.H. auteur aut IRD Mapes R.H. auteur aut IRD Cochran J.K. auteur aut IRD Lignier V. auteur aut IRD Hembree D.I. auteur aut IRD Goiran C. auteur aut IRD Folcher Eric auteur aut IRD Brunet P. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Exploration of a landlocked cenote on Lifou (Loyalty Islands) revealed 37 shells of the cephalopod Nautilus macromphalus Sowerby, 1849, in saltwater on the cenote floor, approximately 40 m below the water surface. The occurrence of these shells is unusual because N. macromphalus is restricted to the open marine waters surrounding the island. All of the shells are mature, and nearly all of them are unbroken, with faded red-brown color stripes. We analyzed seven shells to determine their age. Radiocarbon dating yielded ages of 6380¡30 to 7095¡30 y BP. The 238U-series radionuclides 210Pb (half-life 522.3 y) and 226Ra (half-life 51600 y) also were measured. Two of the samples showed radioactive equilibrium between the nuclides, consistent with the old radiocarbon dates, but the other five samples showed excess 210Pb. When corrected for radioactive decay, the 226Ra activities were much greater than those found in living Nautilus. We conclude that exposure to high activities of 222Rn and 226Ra in the salty groundwater of the cenote altered the activities originally incorporated into the shells. Human placement of the shells in the cavity is rejected based on their radiocarbon age and the geometry of the cenote. The most probable explanation is that the animals entered the flooded karstic system through a connection on the seaward side at approximately 7,000 y BP, during an interval of slowly rising sea level. Unable to find an exit and/or due to anoxic bottom waters, the animals were trapped and died inside. The open connection with the sea persisted for ,700 y, but after ,6400 y BP, the connection was lost, probably due to a roof collapse. This is a rare example of Nautilus in a karstic coastal basin and provides a minimum age for the appearance of N. macromphalus in the Loyalty Islands. specialized INVERTEBRE AQUATIQUE NIVEAU MARIN DATATION PALEONTOLOGIE NAUTILE NOUVELLE CALEDONIE LOYAUTE LIFOU 034BIOINV05 e113372 [13 ] 2014 1932-6203 https://www.documentation.ird.fr/hor/fdi:010065811 10.1371/journal.pone.0113372 1932-6203 [F B010065811] https://www.documentation.ird.fr/hor/fdi:010065811 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers15-11/010065811.pdf IRD - Base Horizon / Pleins textes 2015-08-19 2015-11-27 fdi:010065811 fre