Barnacles, their molluscan hosts, and comparative ecology in the St. Mary’s Formation (late Miocene) of Maryland, USA

Abstract

AbstractFossils can inform the study of modern ecosystems by showing how species interactions in ancient communities compare with those today and how extinction is selective not only with respect to species but also with respect to entire modes of life. We studied the life habits and pattern of occurrence of the barnacleChesaconcavus chesapeakensisZullo, 1992 on the shells of the gastropodConradconfusus parilis(Conrad) and the bivalveChesapecten santamaria(Tucker) from Chancellor’s Point in the Windmill Point Member of the St. Mary’s Formation (late Miocene, Tortonian) of Maryland. Using several criteria, we show that the barnacle occupied living hosts only. The 59% incidence of the barnacle onConradconfusus parilisis high compared to known living associations between barnacles and gastropods. AlthoughConradconfusus pariliswith and without barnacles do not differ in size, suggesting that the barnacle had little effect on this gastropod, there is some indication thatChesapecten santamariawith barnacles are somewhat smaller than those without and may therefore have been adversely affected by the presence of barnacles. On the basis of morphology and the low (15%) incidence of repaired scars,Conradconfusus pariliswas a predator that did not use its shell lip to subdue prey. No ecological equivalents ofConradconfususandChesaconcavushave existed in the temperate northwestern Atlantic between Cape Cod and Cape Hatteras for the past three million years.