Summary of North American Blancan Nonmarine Mollusks1
MALACOLOGIA , 1966, 4(1): 1-172 SUMMARY OF NORTH AMERICAN BLANCAN NONMARINE MOLLUSKS1 D. W. Taylor U. S. Geological Survey, and Research Associate, University of Michigan Museum of Zoology, Ann Arbor, Michigan, U. S. A. ABSTRACT All known North American nonmarine mollusks of Blancan (late Pliocene and early Pleistocene) age have been here fitted into the available framework of associated fossils, physical stratigraphy and radiogenic potassium-argon dates. Many of the independently dated molluscan assemblages are so similar to other faunas that most of the fossils summarized can be assigned confidently to the Blancan age. These assignments permitted compilation of lists of last appear- ances of genera and families that are unknown during or after Blancan times. About 50-55 Blancan assemblages are known, and together with about 10-15 older or younger faunas included for convenience of discussion they are summarized under 57 local geographic headings (map, Fig. 1). For each local assemblage the following data have been given so far as possi- ble: location, previous references to mollusks, stratigraphic unit and most recent geologic maps, number of species of mollusks, mention of other fossils from the same locality or formation, age, institution where fossils are preserved, and most recent topographic maps. The detail of treatment varies widely, according to available information, progress of knowledge since previous liter- ature and the usefulness of new information. Lists of species are included usually only if the fauna is revised or first recorded in this paper, but the references to previous work are intended to be complete. The Blancan faunas from the Great Plains region (Nebraska, Kansas, Okla- homa, Texas), and from Arizona, are generally similar and include mainly widespread living species.
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