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Journal of Paleontology

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THE EVOLUTIONARY AND BIOGEOGRAPHIC ORIGINS OF THE ENDEMIC PECTINIDAE (MOLLUSCA: BIVALVIA) OF THE GALÁPAGOS ISLANDS

¹ Department of Paleobiology, National Museum of Natural History, Washington, District of Columbia 20013-7012, <wallert{at}si.edu>

New phylogenies of endemic Pectinidae of the Galápagos Islands allow their endemic status to be assessed relevant to the relict theory of insular endemism. Nodipecten magnificus and Leopecten isabelensis n. sp. are neoendemic species that evolved in the Pliocene from ancestors in the tropical eastern Pacific and more remote ancestors in the Tertiary Caribbean Province before closure of transisthmian seaways. Spathochlamys vestalis, an eastern Pacific species whose incipiently neoendemic Galápagos representatives have diverged only slightly from the mainland stock, is related to an extant, broadly distributed western Atlantic sister species, S. benedicti, which has an ancestry traceable back to the Miocene in the Tertiary Caribbean Province. Euvola galapagensis is a paleoendemic whose ancestral lineage is extinct on mainland coasts. Veprichlamys incantata is a paleoendemic with an exclusively Pacific history, with its probable immediate ancestor occurring in the Pliocene of Ecuador and its more remote Miocene ancestors in the cooler waters of the southeastern Pacific. The high frequency of endemism and the evidence that originations are Pliocene or later are consistent with the high rates of morphological evolution attained by the Pectinidae relative to many other bivalves.

New species described are L. isabelensis of the Galápagos Islands and L. cocosensis of Cocos Island. Leopecten is shown to be restricted to the Americas and to differ morphologically from Flabellipecten, an extinct Neogene European genus that is phylogenetically not closely related. Based on a new phylogeny, the genus Lyropecten is extinct, and living representatives of the Lyropecten-Nodipecten clade are all in the genus Nodipecten.