2000 GSA Annual Meeting -- Reno, Nevada
2000 GSA Annual Meeting -- Reno, Nevada
Author(s): HENDRICKS, Jonathan R., Department of Geological Sciences, Snee Hall, Cornell University, Ithaca, NY 14853; ALLMON, Warren D., Paleontological Research Institution, 1259 Trumansburg Road, Ithaca, NY, 14850, wda1@cornell.edu
Keywords: Conus, Sinistral, Coiling, Pinecrest, Neogastropoda
The neogastropod genus Conus (Conidae), comprised of over 1500 extant and fossil species and with an evolutionary history spanning at least 55 million years, is composed almost exclusively of members with dextrally coiling (right-handed) shells. The only known exception to this convention occurs in the Neogene of the southeastern United States in which a widely distributed complex of sinistrally coiling (left-handed) species arose. In the richly fossiliferous, Pliocene age Pinecrest beds of southern Florida, a single highly morphologically variable sinistral species, Conus (Contraconus) adversarius Conrad, is particularly common and is also recognized in Neogene deposits from other Florida localities, as well as North Carolina, South Carolina, Maryland, and Virginia. C. adversarius may be the most abundant cone species in the Pinecrest beds, which contain a minimum of 14, but perhaps as many as 34, species of Conus. Four additional sinistral cone species have been named in the Pinecrest beds, although a preliminary morphometric survey strongly suggests that at least two of these fall within the range of variation expressed by C. adversarius and should be regarded as synonyms. It is not known why there are so many sinistral Conus shells in the Pinecrest beds. Possibly a combination of intrinsic and extrinsic factors that may suppress sinistral coiling in Conus (e.g., developmental mode, nutrient availability, substratum type, water temperature, or salinity) were relaxed during the Neogene in the southeastern United States, allowing this complex to evolve and flourish.
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