• Anti-predation strategy, growth rate and extinction amongst Pliocene scallops of the US eastern seaboard

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Sloane, Hilary J.; Schoene, Bernd; Surge, Donna; University of Derby; University of Loughborough; British Geological Survey; University of Mainz; et al. (2017-07-07)
      Placopecten, Chesapecten and Carolinapecten are scallop (pectinid bivalve) genera occurring in the Pliocene of the US eastern seaboard. The first, present in the area today, is a smooth, streamlined form, adept at escaping predators by swimming (‘flight’ strategy). The other two, which are extinct, are plicate (‘ribbed’) forms. Plication facilitates a ‘resistance’ strategy towards predators which is benefited by large size and high shell thickness - maximally so if these states are achieved early in life. Oxygen isotope (δ18O) profiles show that early ontogenetic extensional growth in Pliocene Placopecten was at the same moderate rate as in modern Placopecten. By contrast, in Chesapecten it was as fast as in the fastest-growing modern scallop (c. 80 mm/annum), and accompanied by development of an unusually thick shell, while in Carolinapecten it was substantially faster still (<140 mm/annum). Rapid growth in Chesapecten and Carolinapecten may have been enabled by high primary productivity, which is indicated by the abundance, diversity and large size of co-occurring vertebrates. The extinction of Chesapecten and Carolinapecten, and the survival of Placopecten, can be attributed to a decline in primary productivity which prevented a maximally effective ‘resistance’ strategy towards predators but had no deleterious impact on a ‘flight’ strategy.