First fossil evidence of a drill hole attributed to an octopod in a barnacle

All modern cephalopods are versatile, opportunistic predators employing a variety of hunting techniques such as ambushing, luring, stalking, camouflaging and pursuing (Boyle & Rodhouse 2005). Extant octopods (Octopodidae) prey on a host of organisms including crustaceans, fish, molluscs, cephalopods, polychaetes, ophiuroids and foraminifers, and are able to structure subtidal communities (Nigmatullin & Ostapenko 1976; Moriyasu 1981; Nixon & Young 2003; Boyle & Rodhouse 2005). The methods of preying used by octopods are to capture with their arms and interbrachial web followed by pulling apart shells (McQuaid 1994), biting with the beak (Dodge & Scheel 1999; Voight 2000) or drilling (e. g. Nixon in press). Drilling frequently takes place in decapod crustacean prey (e. g. Boyle & Knobloch 1981), in mollusc shells (e. g. Nixon & Maconnachie 1988; Fig. 2, pls. I-VII), and also in modern barnacles, although rarely reported (Guerra & Nixon 1987; Nixon & Maconnachie 1988; Barnes 1999). Drilling predation in the Cenozoic fossil record is a well-studied phenomenon. Most of the work has focussed on drill holes inferred to be produced by gastropods in shells of both bivalves and gastropods (e. g. Kowalewski et al. 1998; Kelley & Hansen 2003; Klompmaker 2009; Chattopadhyay & Dutta 2013), but these predatory drill holes are also known from other invertebrates such as echinoids (Kowalewski & Nebelsick 2003; Zlotnik & Ceranka 2005), scaphopods (Yochelson et al. 1983; Klompmaker 2011), ostracods (Reyment et al. 1987; Reyment & Elewa 2003), polychaete annelids (Klompmaker 2012; Martinell et al. 2012), brachiopods (Baumiller et al. 2006) and barnacles (Gordillo 2013). Predation evidence of ancient octopods is, to date, inferred only from drill holes. The first report, known to us, of drill holes attributed to ancient octopods is that of Robba & Ostinelli (1975) showing Pliocene bivalves and gastropods from Italy exhibiting such holes. To describe these trace fossils more systematically, Bromley (1993) erected the ichnotaxon Oichnus ovalis for oval drill holes and he also documented similar drill holes attributed to octopods in scallops from the Pliocene of Greece, whereas Harper (2002) reported on similar-shaped drill holes in Plio-Pleistocene scallops from Florida. It should be noted that octopod drill holes do not have a uniform shape, as subcircular drill holes are also known (e. g. Arnold & Arnold 1969; Fig. 2C, H; Nixon & Maconnachie 1988; pl. 3A) and can be classified as O. simplex instead of O. ovalis. Renewed interest in this type of predation is evidenced by Todd & Harper (2011), who attributed subcircular drill holes in an Eocene bivalve to octopods, and Klompmaker et al. (2013) showed the presence of oval drill holes attributed to octopods in Plio- and Pleistocene decapod crustaceans. The goal of this study is to report the first fossil evidence of a drill hole in a barnacle that can attributed to an octopod, thereby adding to the growing body of evidence of octopods drilling prey during the Cenozoic. The drill hole microhabitat was subsequently fouled by an encrusting foraminifer.