186


Journal of Paleontology 92(2):183–188


(Bruguière) in Hong Kong (Chan and Chan, 2005). Similar effects were detected in the mussel Mytilus edulis Linnaeus in Germany (Buschbaum and Saier, 2001) and the scallop Chlamys hastata (Sowerby) in British Columbia (Farren and Donovan), and especially in Mizuhopecten yessoensis (Jay) in eastern Russia (Silina and Zhukova, 2016). A heavy load of barnacles impedes the escape response of the Californian Norrisia norrisi (Schmitt et al., 1983). Such effects would not apply to the sedentary Trichotropis cancellatus and would likely have been minor for Conradconfusus parilis, which like most living buccinids would not have had a well-developed escape response to predators.


Mode of life of Conradconfusus parilis.—The presence of abundant barnacles on living individuals, together with details of shell form and sculpture, indicate that Conradconfusus par- ilis was an epifaunal predator. The strong spiral cords, wide rounded axial ribs, angular whorl profile, and axially straight siphonal canal are consistent with an epifaunal mode of life and inconsistent with the burrowing habit (Vermeij, 2017). The species lacks adaptations such as ratchet sculpture, a stream- lined shape, and other features often or invariably associated with active infaunal locomotion. The profile of the outer lip of the shell of Conradconfusus


parilis is planar when seen from the ventral side. The planar lip implies that Conradconfusus parilis employed neither wedging nor chipping as a method of feeding, which is associated with a convex outer lip (see Introduction). Moreover, only four of 27 individuals (15%) show signs of shell repair,with only one repair per individual, indicating that the species did not damage the shell lip during feeding and that shell breakage by predators was rare. Where damage occurs, it extends overmuch of the contour of the last whorl, in one case including the siphonal canal, and is thus not limited to the central sector as it is in convex-lipped species that chip or wedge their prey. In these latter species, shells are damaged repeatedly, often showing 10 or more scars per shell in living busyconine and fasciolariine gastropods. These inferences are supported by the known diets of


morphologically similar living species. A planar outer lip, horizontally straight and extended siphonal canal, angular whorl profile, and variably developed symmetrical spiral and axial sculptural elements characterize many melongenids (Hemifusus, Pugilina, Rexmela, and Volegalea), the fasciolariid Triplofusus, buccinids (Kelletia, Neptunea, and Penion), and the turbinellid Syrinx. The melongenids feed on mollusks and, in the case of Volegalea cochlidium (Linnaeus), on barnacles, either by suffocating the prey in the foot or by stealthily approaching prey and then rapidly inserting the proboscis between valves or into the aperture (Morton, 1985, 1986; Matthews-Cascon et al., 1990; Bowling, 1994; Tan and Phuah, 1999; for updated taxonomy of melongenids, see Vermeij and Raven, 2009; Landau and Vermeij, 2013; Abbate and Simone, 2015). Species of Neptunea feed on completely closing bivalves and on polychaetes, again by inserting a long proboscis (Shimek, 1984). Kelletia kelleti (Reeve) feeds on bivalves and carrion (Rosenthal, 1971). Unlike fasciolariids with a medially convex outer lip, which wedge or chip bivalve prey, species of Triplofusus feed on bivalves and gastropods with methods similar to those of melongenids and Neptunea (Kent, 1983;


Stupakoff, 1986). Syrinx aruanus Linnaeus feeds on large tube- dwelling infaunal polychaetes by thrusting its very long proboscis into the tubes while remaining on the sediment surface (Taylor and Glover, 2003). Planar-lipped individuals of the buccinid Buccinum undatum Linnaeus also do not wedge or chip their bivalve prey, unlike individuals of the same species with a convex lip (Nielsen, 1975; Scolding et al., 2007). From these modern examples, we conclude that Conradconfusus parilis fed on prey mollusks and/or polychaetes and perhaps barnacles without the use of its outer lip to subdue prey.


Comparison with modern communities.—The genus Con- radconfusus became extinct at the end of the Miocene (Petuch,


1993). Not only did it fail to leave descendants, but no gastropod fills its ecological role in the modern northwestern Atlantic fauna on the coast between Cape Cod and Cape Hatteras. Modern predatory gastropods in this region today include large infaunal drilling naticids, small drilling muricids, and large shell-wedging and shell-chipping semi-infaunal busyconine whelks. Large drilling muricids, represented in Miocene and Pliocene communities of the northwestern Atlantic by species of Ecphora (Casey et al., 2015), also disappeared. In short, the extinction of large epifaunal predatory gastropods left an eco- logical void that has not been reoccupied in the temperate northwestern Atlantic. The high abundance of large barnacles on shells and other


substrates, together with other evidence, points to high planktonic primary productivity at Chancellor’s Point. Experi- ments in the Java Sea, which like the Neogene Chesapeake region is an epicontinental sea, have shown that abundant suspension-feeding epibionts on shells are associated with high plankton concentrations (Lescinsky et al., 2002). The fauna of the Java Sea includes large suspension-feeding bivalves (Placuna, Anadara) and gastropods (Turritella) as well as large predatory gastropods (Hemifusus). Likewise, at Chancellor’s Point, large barnacles lived alongside very large suspension- feeding bivalves of the genera Chesacardium, Chesapecten, Costaglycymeris, Dallarca, Glossus, Mercenaria, and Panopea. Together with large predatory Ecphora and Conradconfusus, these genera show size increases from the early Miocene to the late Miocene and in some cases the Pliocene (Vermeij, 2012), indicating that planktonic productivity rose during this interval in the Chesapeake region. Late Pliocene cooling and the ensuing Pleistocene glacia-


tions ended this trend and radically changed community composition in the temperate northwestern Atlantic. Along with some small-bodied clades, most large-bodied lineages of mollusks with a maximum shell dimension of 5 cm or more became globally or regionally extinct. These include epifaunal Chesaconcavus, Chesapecten, Conradconfusus, Conradostrea, Crucibulum, Ecphora, Hippochaeta, Mariafusus, and Perna; soft-bottom epifaunal to semi-infaunal gastropods Coronaful- gur, Scaphellopsis, Sycopsis, Turrifulgur, and Volutifusus; nonsiphonate soft-bottom bivalves Costaglycymeris, Dallarca, Granoarca, Glossus, and Marvacrassatella; and siphonate burrowing bivalves Chesacardium, Dosinia, Leptomactra, Mactrodesma, Panopea, and Stewartia (Ward, 1992; Zullo, 1992; Petuch, 1993, 2004; Vermeij et a1., 2008; Vermeij, 2012). Chesapeake lineages of large size surviving to the Recent in the


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