The endolithic life habit has evolved several times in the Bivalvia, e.g., in the superfamilies Modiolopsoidea (family Modiolopsidae), Mytiloidea (family Mytilidae, subfamily Lithophaginae), Arcoidea (family Arcidae), Cardioidea (family Tridacnidae), Veneroidea (family Petricolidae), Gastrochaenoidea, Myoidea (family Myidae), Hiatelloidea, and Pholadoidea (families Pholadidae and Teredinidae) (Otter, 1937; Yonge, 1963; Cox, 1969; Carter, 1978; Kleemann, 1980). The oldest known definite bivalve borings are Ordovician slotlike depressions in stromatoporoids, made by the facultative nestler/borer modiolopsid Corallidomus Whitfield, 1893 [1895] (Pojeta and Palmer, 1976; Wilson and Palmer, 1988). Pojeta and Palmer (1976) and Morton (1990) cited Corallidomus as the ancestor of the Lithophaginae. However, lithophaginids more likely evolved from modiolinid mytilids, which in turn evolved from modiolopsids (Fang and Morris, 1997; Fang, 1998; Carter et al., 2000). Lithophaga-like shells are known from the Carboniferous and Permian, but these Upper Paleozoic examples are not known to have been endolithic (Kleemann, 1983, 1990, table 2). Wilson and Palmer (1998) attributed certain borings without associated shells in Upper Carboniferous limestone cobbles to lithophaginids because the borings are widest near their anterior end and they lack a constricted neck. However, if, as Wilson and Palmer suggested, these borings are not posteriorly truncated, then their openings are relatively much wider than typical lithophaginid borings. One boring illustrated by Wilson and Palmer (1998, fig. 4) has an irregular anterior cross-sectional shape that is unlike lithophaginid and gastrochaenid borings. This irregularity recalls the Early Ordovician ichnospecies Gastrochaenolites oelandicus Ekdale and Bromley, 2001, which is similarly vase-shaped. Ekdale and Bromley (2001) noted that the latter boring predates known endolithic bivalves, so they attributed it to an unknown invertebrate.