80 Paleontology II, Mesozoic and Cenozoic (Posters)

Tuesday, 16 March 2010
1:30 PM - 5:35 PM
International ABCDF

DIVERSITY PATTERNS OF MOLLUSCS ACROSS THE MULTI-PHASED PLIO-PLEISTOCENE MASS EXTINCTION IN NORTH CAROLINA

Paper number: 80-10
Program: Technical Sessions
Time: 1:30 PM – 5:35 PM

Authors

Abstract

Plio-Pleistocene western Atlantic molluscs experienced a multi-phased mass extinction. To clarify timing of the extinctions, we examined diversity of Plio-Pleistocene mollusc faunas as part of a Research Experiences for Undergraduates program. Bulk samples were collected from the Duplin Formation (Natural Well site at Magnolia, NC); Colerain Beach Member of the Chowan River Formation (Colerain, NC); lower James City Formation at Lee Creek Mine (Aurora, NC) and the upper James City on the Neuse River (James City, NC). Samples of an unnamed Pliocene unit (Yorktown Formation?) were collected at a granite quarry at Fountain, NC. Samples were sieved through a quarter-inch mesh and specimens with beaks (bivalves) and apices (gastropods) were picked, sorted and identified to genus level and counted. The study included >1,000 gastropods and ~13,000 bivalves. Results were combined with our 2008 REU data (~14,000 specimens from the Duplin Formation on the Lumber River and lower Waccamaw Formation, Columbus County, NC). Genus-level richness was compared among units using rarefaction; bivalve richness was rarefied to 360 specimens and gastropods to 130 specimens (size of the smallest samples).

As expected, richness was greatest in the Duplin Formation prior to onset of extinction. Gastropod richness was similar and greatest in the Duplin on the Lumber River and at Magnolia (44 and 46 genera; rarefied richness ~25 genera). Bivalve richness was also greatest in the Lumber River Duplin (66 genera, 40 rarefied genera), though Magnolia bivalves were less diverse (42 genera, 23 rarefied genera). Bivalve diversity declined significantly from the Duplin to lower Waccamaw (41 genera, 35 rarefied genera) and lower James City (45 genera, 26 rarefied genera). Rarefied gastropod richness was also less (~16 genera) for both lower Waccamaw and lower James City Formations. Chowan River richness was similar to the lower James City (18 and 26 rarefied gastropod and bivalve genera). In the upper James City, although gastropod richness remained similar (18 genera, 16 rarefied genera), bivalve diversity dropped markedly (25 genera, 19 rarefied genera). The unusual, barnacle-dominated assemblage at the Fountain Quarry had lower richness than expected for a pre-extinction fauna (20 and 17 rarefied gastropod and bivalve genera respectively).