| Previously unknown Mio-Pliocene relict molluscan assemblages have been found to exist in pockets in shallow water along northern Columbia and Venezuela. Thirty-five relict gastropod species of the families Turritellidae, Calyptraeidae, Cypraeidae, Cassidae, Ficidae, Columbellidae, Buccinidae, Fasciolariidae, Olividae, Mitridae, Volutomitridae, Volutidae, Marginellidae, Cancellariidae, Conidae, Terebridae, and Turridae, are described and their Recent and fossil distributions outlined. Based on the unusual ecological conditions in which the relicts have been found to be living, the environment of the Neogene Caribbean region is reconstructed and a new model of Neogene provinciality is proposed. A synthetic working definition of provinciality is given and, using this, two new Neogene molluscan provinces, the Caloosahatchian and the Gatunian, are described. The evolution of their gastropod faunas is traced from the Lower Miocene to the Upper Pliocene, and into the Recent as the Gatunian relict pocket. To explain both the existence of the relicts and their affinities with the Recent Panamic fauna, a new model of Upper Pliocene biological catastrophism and extinction is proposed, incorporating aspects of the effects of the closing of the Isthmus of Panama and glacially induced sea level fluctuations and temperature changes. |
