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Neogastropoda, Opisthobranchia, and Basommatophora from the Ripley, Owl Creek, and Prairie Bluff Formations

1964; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp331b

2330-7102

Norman F. Sohl,

Marine Biology and Ecology Research

Description of the gastropods found in the Upper Cretacsous (Late Campanian-Maestrichtian) deposits of southwestern Tennessee and northeastern Mississippi is concluded in this chapter.A discussion of the major monographed gastropod faunas of the geologic column indicates that there is a decided progression with decreasing age as to the percentage representation of the Archaeogastropoda, Mesogastropoda, and Neogastropoda of any given fauna.Paleozoic gastropod faunas were dominated by the Archaeogastropoda.The Mesogastropoda grew in proportional abundance at the expense of a decrease in Archaeogastropoda until they became the dominant group during most of the Mesozoic.About 50 percent of the represented species and genera of any Upper Cretaceous gastropod fauna were mesogastropods.The Neogastropoda became the dominant group, in terms of the number of species and genera in the Tertiary.The graphs presented indicate that the gastropod fauna of the Ripley, Owl Creek, and Prairie Bluff Formations was unique among Upper Cretaceous faunas in that the Neogastropoda were dominant and the percentage representation of the various groups mirrors that of the Tertiary and Recent fauna.The gastropod fauna of the Ripley Formation was perhaps the largest in terms of species and genera of any known Upper Cretaceous formation.The literature offers little information pertinent to determining its development.New evidence derived from preliminary studies of the gastropod faunas of the Chattahoochee River region of Georgia and Alabama indicates that the major Ripley faunal components are well developed in the Eutaw Formation (Santonian).Knowledge of the Turonian Gastropoda of the gulf coast is lacking.The Woodbine (Cenomanian) faunas of Texas show numerous similarities with the Comanche faunas (Lower Cretaceous) and few similarities with the Ripley or later Upper Cretaceous faunas.Therefore, the Ripley faunas did not appear suddenly but developed gradually from Coniacian and possibly Turonian time through the late Upper Cretaceous.Analysis of the Upper Cretaceous faunas of the world indicates broad outlines of possible zoogeographic provinces.Although specific and generic similarities between the gulf coast Ripley faunas and those of other areas are small, save for cosmopolitan genera, gross aspect and composition of many are similar.The faunas of other zoogeographic realms such as those of Pondoland, Union of South Africa, northern Germany (Aachen and Limburger Kreide), and those of southern India all show a gross similarity, especially when compared to those of the Caribbean, Gosau, north Africa, the Middle East, or Baluchistan.These differences appear to be due to the proximity to, or being a component part of, the Tethyan Belt.The former are ecologically similar.For the most part these were sand-facies faunas and generally occupied coastal embayments outside of the major Tethyan sphere of influence.The main body of this report consists of the systematic description of the Ripley, Owl Creek, and Prairie Bluff species of the Neogastropoda, Opisthobranchia, and Bassomatophora.There are 210 species and subspecies described and formally named.Fifty-two species represented by inadequate material are only tentatively assigned or are merely mentioned.Of the 210 named species, 77 are described as new.These species are assigned to 95 genera and subgenera.Of the genera and subgenera Lowenstamia and Ornopsis (Pornosis) are proposed as new.