Edge-drilling on the brachiopod Perditocardinia cf. P. dubia from the Mississippian of Missouri (USA)

Examination of a bulk sample of the Mississippian orthide brachiopod Perditocardinia cf. P. dubia revealed borings in 25.8% of the 259 specimens. The drillholes are small (0.13–0.80 mm in diameter), round, and each brachiopod has been drilled only once. Normally, Paleozoic brachiopods are drilled at a low frequency (<5%) and the placement of the drillhole is directly over the viscera of the animal. The majority of the specimens of P. cf. P. dubia in this sample, however, are drilled directly on the anterior margin; this is the first documentation of Paleozoic edge-drilling on brachiopods. The high frequency of boring and especially the location of drillholes near the margin, suggest either a different predatory/parasitic organism or a different feeding behavior than is commonly associated with Paleozoic brachiopods. These drillholes may represent a behavior analogous to modern capulid gastropods that parasitize bivalves by positioning themselves along the host’s commissure and sometimes drilling the shell. It could also represent a behavior similar to modern naticid gastropods, which drill along the commissure of its bivalve prey. Regardless, this example further illustrates that the Paleozoic was characterized by a broader repertoire of drilling behaviors than has been previously recognized.