Part of the fascination with fossil shells is the excellent preservation which occurs under the proper conditions. With the exception of color, specimens whether shell, coral, or echinoderm, many times look as if they were picked off of a beach. Yet careful examination reveals differences between fossil and recent related species which demonstrate changes within taxa through time. Often overlooked however, are the geological processes which form shell beds. A principle of global geology is transgressive/regressive sea level rise. During warm periods, less water is captured in ice caps and glaciers resulting in a rise of sea level. As oceans encroach upon dry land (transgression) marine environments move accordingly and remains of organisms become deposited within building sediments. The process is not linear but gradual and the remains of these organisms are concentrated through currents and storms in dense accumulations by the process known as winnowing. As water levels continue to rise, the shallow marine zones which contain the most abundant life move according to optimum depth. Sediments continue to accumulate but into zones containing few macro organisms. When global temperatures drop, water is once more captured in ice and a regression of the oceans occur which remove sediment as sea levels retreat sometimes removing fossiliferous zones created during the previous transgression. When the next transgression cycle occurs, shell bed formation can be deposited on top of an older bed resulting in a time gap or unconformity. In Florida, species identification based upon age is particularly difficult where the southern most part of the state is only a few feet above sea level and fossils can only be obtained from quarries in which mining might go through several different beds producing specimens out of spacial context (fig. 1).
Figure 1. SMR Aggregates Phase 10 Pit, Sarasota County, Florida. November 2013.
During the late Pliocene one such period of warming produced shell beds worldwide which can be correlated as to age on the basis of calcareous nanofossils and magnetostratigraphy. This period is called the Piacenzian stage based upon the incredibly rich shell beds near the Italian city of Piacenza. During this period Italy was no more than a sliver of land with the Adriatic reaching as far west as Turin. In northern Europe the English Channel was much wider as sea levels flooded west to London and eastward over much of the Netherlands and East Flanders. There was not a arctic ice cap and sea otters ranged up to the northern shore of Alaska where their fossilized remains have been found. In the Southern Hemisphere, the high southern shore of Australia was flooded as much of the Nullabor Plain was a shallow sea (fig. 2).
Figure 2. Selected Piacenzian Gastropods. From left to right: Aphorrais pespelecani (Linne, 1758) Piacenzian Stage, Valchiavenna, ITALY; Nassa reticosa J.Sowerby, 1815, Red Crag Formation, Walton-on-the-Naze, Essex, UK; Cassis fimbriata Quoy & Gaimard, 1833, Roe Calcaranite, Madura, Western AUSTRALIA; Opalia varicostata anomala (Stearns, 1875), San Diego Formation, San Diego County, California USA.
The main regional geological event in North America just prior to the Piacenzian was the final closure of the Central America isthmus which forced warm equatorial waters up the North American eastern seaboard producing a local marine mass extinction. The Atlantic Ocean flooded the Salisbury Embayment covering much if not all of the Delmarva Peninsula, eastern Maryland and Virginia almost to the fall line in northeastern North Carolina. The shell beds formed here are referred to as Zone 2 Yorktown Formation. Further south the Western Atlantic extended from a line west of Robeson, North Carolina; Florence, South Carolina; the Okefenokee Basin in Georgia and Jacksonville, Florida. A secession of beds were laid down in this area during the Piacenzian, the best known being the Duplin Formation. The northern Gulf of Mexico reached almost to the Georgia state line depositing the Jackson Bluff formation while in the flooded Everglades Basin, the Tamiami Formation was formed. All of these beds can be correlated to each other based upon the mollusk taxa that they share (fig. 3).
Figure 3. Some Piacenzian index fossils of the class Gastropoda found within the Southeastern United States. From left to right: Pterorytis umbrifer (Conrad, 1832), Moore House Member of the Yorktown Formation, Chucatuck, Isle of Wight County, Virginia; Sconsia hodgii (Conrad, 1841), Duplin Formation, Bladen County, North Carolina; Ecphora quadricostata (Say, 1824), Jackson Bluff Formation, Alum Bluff, Liberty County, Florida; Fasciolaria rhomboidea Rogers, 1839, Pinecrest Member of the Tamiami Formation, SMR Phase 10, Sarasota County, Florida.
This post represents an update to my Pliocene Project which I began in early 2012 resulting in a species list in 2013 of my Upper Pliocene collection organized and cross-referenced according to species found across the southeastern United States. Between that initial compilation and this one, however, I found that the methodology in which I performed identification was flawed. It is easy enough identify species one location at a time and to organize a collection by horizon, however when I began looking at those identifications side by side I found that there were errors. To rectify the discrepancies I reorganized my collection taxonomically as opposed to stratigraphically. Although this led to a great deal of invested time, the deep dive into taxonomy using descriptions within the original references has improved the accuracy and the confidence that have with the phylum mollusca, which I like to refer to as the “insects of the sea” based upon their numerical diversity. The expansion of the Piacenzian species list below includes the additions from my collecting efforts in the Tamiami Formation in 2013 and from the Chowan River Formation in 2014. A few corals, mollusks, and vertebrates were added to the list from the Pinecrest however the list was significantly increased with mollusks from the Chowan River Formation which introduced a number of Lower Pleistocene mollusks which first appeared towards the end of the Pliocene.
My plan is to periodically update the list as I will continue to collect within the Piacenzian particularly at SMR prior to its closure. Also on tap for 2015 is a concerted effort to investigate Duplin deposits in the Carolinas which contain many endemic species and is represented in my collection from only two localities.
Although I have previously listed many of the references below these are the ones that I have used the most for species identification. The website for the World Register of Marine Species (WoRMS) has been particularly useful for providing the most updated names of mollusk genera.
Bouchet, P., Yu. I. Kantor, A.Sysoev and N. Puillandre. 2011. New Operational Classification of the Conoidea (Gastropoda). Journal of Molluscan Studies (2011) 77: 273–308.
Campbell, Lyle. 1975. Check List of Marine Pliocene Mollusks of Eastern North America in Plio-Pleistocene Faunas of the Central Carolina Coastal Plain. Geologic Notes (South Carolina Division of Geology) Vol. 19, No. 3.
Campbell, Lyle. 1993. Pliocene Molluscs from the Yorktown and Chowan River Formations in Virginia. Virginia Division of Mineral Resources Publication 127.
Dall W.H. 1890-1903. Contributions to the Tertiary Fauna of Florida, with Especial Reference to the Miocene Silex-Beds of Tampa and the Pliocene Beds of the Caloosahatchie River, Part I: Pulmonate, Opisthobranchiate and Orthodont Gastropods, Transactions of the Wagner Free Institute of Science of Philadelphia 3(1-VI).
Gardner, J. A. 1944. Mollusca from the Miocene and Lower Pliocene of Virginia and North Carolina: Part 1. Pelecypoda, United States Geological Survey Professional Paper 199-A: iv, pages 1-178, plates 1-23
Gardner, J. A. 1948. Mollusca from the Miocene and Lower Pliocene of Virginia and North Carolina: Part 2. Scaphopoda and Gastropoda, United States Geological Survey Professional Paper 199-B: iv, pages 179-310, plates 24-38, [iii]
Gardner, J. A. and T.H. Aldrich. 1919. Mollusca from the Upper Miocene of South Carolina: with Descriptions of New Species. Proceedings of the Academy of Natural Sciences of Philadelphia 71: pages 17-53.
Gibson, Thomas G. 1987. Miocene and Pliocene Pectinidae (Bivalvia) from the Lee Creek Mine and Adjacent Areas in Geology and Paleontology of the Lee Creek Mine, North Carolina, II. Smithsonian Contributions to Paleobiology No. 61.
Hendricks, Jonathan. 2008. The genus Conus (Mollusca: Neogastropoda) in the Plio-Pleistocene of the southeastern United States, Bulletins of American Paleontology 375.
Hulbert, Richard C. (ed.). 2001. The Fossils Vertebrates of Florida. University Press of Florida.
Mansfield, W.C. 1930. Miocene Gastropods and Scaphopods of the Choctawhatchee Formation of Florida, Florida Geological Survey Bulletin 3, 189 pages.
Mansfield, W.C. 1931. Some tertiary mollusks from southern Florida. Proceedings of the United States National Museum, v. 79.
Mansfield, W.C. 1931. Pliocene Fossils from Limestone in Southern Florida in Shorter Contributions to General Geology, USGS Professional Paper 170, 11 pages.
Mansfield, W.C. 1932. Miocene Pelecypods of the Choctawhatchee Formation of Florida, Florida Geological Survey Bulletin 8, 233 pages.
Mansfield, W.C. 1936. Stratigraphic Significance of Miocene, Pliocene, and Pleistocene Pectinidae in the Southeastern United States, Journal of Paleontology, Vol 10, No. 3, 24 pages.
Mansfield, W.C. 1939. Notes on the Upper Tertiary and Pleistocene Mollusks of Peninsular Florida, Florida Geological Survey Bulletin 18, 128 pages.
Hollister, S.C. 1971. New Vasum Species of the Subgenus Hystrivasum. Bulletins of American Paleontology 262.
Olsson, A.A. 1967 (1993 Reprint). Some Tertiary Mollusks from South Florida and the Caribbean, Originally - Bulletins of American Paleontology 54(242), The Paleontological Research Institute Special Publication 19: pages 11-75, 9 plates
Olsson, A.A., and A. Harbison. 1953 (1990 Reprint). Pliocene Mollusca of Southern Florida with Special Reference to Those from North Saint Petersburg, with special chapters on Turridae by W.G. Fargo and Vitinellidae and Fresh-water Mollusks by H.A. Pilsbry, The Academy of Natural Sciences of Philadelphia Monographs 8, The Shell Museum and Educational Foundation, 457 pages, 65 plates
Olsson, A.A., and R.E. Petit. 1964. Some Neogene Mollusca from Florida and the Carolinas, Bulletins of American Paleontology 47(217): pages 509-574, plates 77-83
Olsson, A.A., and R.E. Petit. 1968 (1993 Reprint). Notes on Siphocypraea, Originally - Special Publication 9, The Paleontological Research Institute Special Publication 19: pages 77-88.
Petuch, Edward J. 1994. Atlas of Florida Fossil Shells (Pliocene and Pleistocene Marine Gastropods). Chicago Spectrum Press.
Portell, Roger W. and Craig W. Oyen. June 2002. Pliocene and Pleistocene Echinoids. Florida Fossil Invertebrates Part 3, 30pp.
Portell, Roger W. and Jeffery G. Agnew. February 2004. Pliocene and Pleistocene Decapod Crustaceans. Florida Fossil Invertebrates Part 4, 29 pp.
Portell, Roger W. November 2004. Eocene, Oligocene and Miocene Decapod Crustaceans. Florida Fossil Invertebrates Part 4, 29 pp.
Rathbun, Mary J. 1935. Fossil Crustacea of the Atlantic and Gulf coastal plain. Geological Society of America. Special papers; no. 2.
Tucker, H.I. and Druid Wilson. 1932. Some new or otherwise interesting fossils from the Florida Tertiary. Bulletins of American paleontology; v. 18: no. 65.
Tucker, H.I. and Druid Wilson. 1933. A second contribution to the Neogene paleontology of South Florida. Bulletins of American paleontology; v. 18: no. 66.
Tuomey, M., and F.S. Holmes. 1855-1856 (1974 Reprint). Pleiocene Fossils of South-Carolina: Containing Descriptions and Figures of the Polyparia, Echinodermata and Mollusca, Original pages 1-30 and plates 1-12 published in 1855, Original pages 31-152 and plates 13-30 published in 1856, The Paleontological Research Institution Special Publication 12: xvi, 152 pages, 30 plates, [addendum]
Turgeon, D.D. et al. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks. Second edition. American Fisheries Society Special Publication. No. 26. 526 pp.
Waller, T.R. 1969. The evolution of the Argopecten gibbus stock (Mollusca: Bivalvia), with emphasis on the Tertiary and Quaternary species of eastern North America. Journal of Paleontology, Memoir 3 (vol. 43, suppl. to No. 5).
Ward L.W. and Blackwelder, B.W. 1975. Chesapecten, a New “Genus of Pectinidae (Mollusca: Bivalvia) from the Miocene and Pliocene of Eastern North America. USGS Professional Paper 861.
Ward, L. W., and Gilinsky, N. L. 1993. Molluscan assemblage of the Chowan River Formation, Part A. Biostratigraphic analysis of the Chowan River Formation (Upper Pliocene) and adjoining units, the Moore House Member of the Yorktown Formation (upper Pliocene) and the James City Formation (Lower Pleistocene): Virginia Museum of Natural History Memoir 3, part A., 33 p.
Williams, Margaret. 2006. Shallow-Water Turridae of Florida and the Caribbean. Self published.
Weisbord, Norman E. 1966. Some late Cenozoic cirripeds from Venezuela and Florida. Bull. Amer. Paleont., vol. 50, no. 225, pp. 1-145, pls. 1-12.
Weisbord, Norman E. 1974. Late Cenozoic Corals of South Florida. Bulletins of American Paleontology vol. 66, no. 285. 544 pp.
Zullo, Victor A., 1992. Revision of the balanid barnacle genus Concavus Newman. Supplement to Journal of Paleontology, v. 66, no. 6, pt. II.
Zullo, Victor A. and Portell, Roger W. 1993. Paleobiogeography of the Late Cenozoic Barnacle Fauna of Florida in The Neogene of Florida and Adjacent Regions, Florida Geological Survey Special Publication No. 37.
The Bailey-Matthews National Shell Museum Southwest Florida Shells http://shellmuseum.o.../shellindex.cfm
Florida Museum of Natural History Invertebrate Paleontology Database http://www.flmnh.ufl.edu/invertpaleo/search.asp
Florida Museum of Natural History Invertebrate Paleontology Image Gallery http://www.flmnh.ufl.edu/invertpaleo/galleries.htm
Fossilworks, Gateway to the paleobiology Database http://fossilworks.org/
Gastropoda Stromboidea http://www.stromboidea.de/?n=Main.HomePage
Greta L. Polites Worldwide Fossil Muricidae Collection http://glpolites.us/murex/index.htm
International Fossil Shell Museum http://www.fossilshells.nl/
Let’s Talk Seashells http://www.letstalkseashells.com/
Natural History Museum Rotterdam Mollusks Database http://www.nmr-pics.nl/
The Neogene Atlas of Ancient Life Southeastern United States http://neogeneatlas.org/
Olividae and Olivellidae Lifedesk – Mollusca http://olivirv.lifedesks.org/
The World Register of Marine Species (WoRMS) http://www.marinespecies.org/index.php