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 = 22.3 y) and 226Ra (half-life = 1600 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.
Division of Paleontology (Invertebrates), American Museum of Natural History, New York, New York 10024, United States of America;North Carolina Museum of Natural Sciences, Raleigh, North Carolina 27601, United States of America;School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York 11794, United States of America;Laboratoire PPME (Pôle Pluridisciplinaire de la Matière et de l'Environnement), Université de la Nouvelle-Calédonie, BP R4, 98851 Nouméa cedex, New Caledonia;North Carolina Museum of Natural Sciences, Raleigh, North Carolina 27601, United States of America;Labex Corail & LIVE (Laboratoire insulaire du Vivant et de l'Environnement), Université de la Nouvelle-Calédonie, BP R4, 98851 Nouméa cedex, New Caledonia;Institut de Recherche pour le Développement, BP A5, 98848 Nouméa cedex, New Caledonia;Independent Researcher, 21 rue Louis Fablet, 94200 Ivry sur Seine, France
Recommended Citation:
Neil H. Landman,Royal H. Mapes,J. Kirk Cochran,et al. An Unusual Occurrence of Nautilus macromphalus in a Cenote in the Loyalty Islands (New Caledonia)[J]. PLOS ONE,2014-01-01,9(12)