42 Paleontology (Posters)

Friday, 11 April 2014
1:00 PM - 5:00 PM
Latham A/B/C

LIFE MODES IN MOLLUSCAN ASSEMBLAGES OF THE LOWER WACCAMAW FORMATION (PLEISTOCENE) OF SNAKE ISLAND PIT IN NORTH CAROLINA

Paper number: 42-5
Program: Technical Sessions
Time: 1:00 PM – 5:00 PM

Authors

Abstract

Specimens obtained from the lower Waccamaw Formation at Snake Island Pit near Old Dock in North Carolina were studied as part of an ongoing research effort to examine extinctions in molluscan faunas during the Plio-Pleistocene. The paleontology class at Georgia State University (GSU) analyzed five bulk samples from this locality (Bags #6–#10) yielding ~5800 specimens (86% bivalves, 14% gastropods). Samples were sieved using a ¼” mesh and intact umbos (bivalves) and apices (gastropods) were picked, sorted, identified to genus, and counted. Life modes were assigned using the NMITA database, which contains information on feeding, attachment, mobility, and substrate relationship for bivalves and feeding for gastropods. Data from a smaller sample of 750+ specimens collected at the same locality and studied previously by University of North Carolina (UNCW) students were used for comparisons. Composition of life modes was analyzed using relative abundance data calculated separately for bivalves and gastropods.

GSU bivalves were dominated by individuals that were unattached (80%), actively mobile (83%), and infaunal (84%) followed by immobile (10%), byssally attached (11%), and epifaunal (13%) bivalves. Feeding categories for bivalves were represented mostly by individuals that were suspension feeders (80%) with chemosymbiotic (9%) and other deposit feeders (8%) less common. Gastropods were comprised mostly of individuals categorized as predatory carnivores (75%) followed by suspension feeders (10%) and herbivores (9%). Life modes have not yet been assigned to all individuals in these samples as 8% of gastropods and 4% of bivalves are still being identified.

Similar patterns for bivalves were found in the UNCW sample, in that most individuals were unattached (68%), actively mobile (66%), and suspension feeders (97%). However, epifaunal and infaunal life habits were evenly represented (51% vs. 49%); very few bivalves were deposit feeders (3%). Bivalves immobile (31%) via cementation (31%) were more common than byssally attached individuals (1%). The distribution of gastropod individuals is represented by increased suspension feeders (53%) and fewer predatory carnivores (45%) compared to the GSU samples. Taxa responsible for differences in the UNCW sample include elevated Crepidula and Conradostrea.