Drill hole convergence and a quantitative analysis of drill holes in mollusks and brachiopods from the Triassic of Italy and Poland

The history of predation is recorded primarily from drilling in Cenozoic invertebrates. Quantitative data are uncommon from the Triassic, a period before the appearance and radiation of many known drill hole producers such as various gastropod families and octopods. We present quantitative evidence of drilling from the Late Triassic (Carnian) Cassian Formation of Italy and the Middle Triassic (Anisian) Lower Muschelkalk of Poland, documenting the first drill holes in Triassic brachiopods. A single brachiopod with a cylindrical, complete drill hole was found in a brachiopod sample from of Poland (drilling percentage = 0.3%, n = 365). The Cassian Formation yielded drill holes in gastropods, bivalves, and brachiopods, indicating that more species are drilled than was known previously. The minimum drilling percentage exclusive of incomplete drill holes of a sample from the Stuores Wiesen (Cassian Formation) is 1.7% (n = 116.5). Prey selectivity is evident: complete drill holes are primarily present in one gastropod species, Polygyrina lommeli (11.8% of specimens with a complete drill hole), whereas other common species were not drilled. Single drill holes in brachiopods are cylindrical and complete and may be predatory in origin. Multiple drill holes in mollusks are common, and drill holes are parabolic and often incomplete with a central boss, resembling the shape of drill holes produced by extant naticid gastropods. A survey of the Paleozoic literature showed that such drill holes are also present in Devonian and Carboniferous brachiopods. However, naticids did not evolve until the Cretaceous so we propose the term drill hole convergence for similar-shaped drill holes produced by different organisms. The Triassic parabolic drill holes are not caused by domicile-seeking or boring organisms. Instead, we favor a predatory origin of these drill holes, but we cannot entirely rule out parasitism. Surveying other Triassic invertebrate assemblages should yield more evidence of drilling. (C) 2016 Elsevier B.V. All rights reserved.