Borings in shells from the Paleozoic are common in fossil assemblages, but their origins are often poorly understood. No consensus has been reached on if these borings represent predatory, parasitic or post-mortem excavations. In this study, observations were made on a large sample size of borings in strophomenides and pentamerides from Late Lochkovian, Wenlock-Ludlow, and Late Ordovician localities in northern Canada and on Anticosti Island. Multivariate statistical analyses were used to identify the origin of the borings and to describe their spatial and temporal trends.
Several hundred borings in Thaerodonta-type and Strophomena-type strophomenides were identified as Oichnus simplex and Oichnus paraboloides. Borings exhibiting characteristics of predation were most common in Devonian Thaerodonta-type strophomenides and Ordovician Strophomena-type strophomenides, while parasitic and post-mortem borings were present in strophomenides of all ages. Cluster Analysis and Principal Component Analysis segregated predatory borings from non-predatory borings, and identified trends related to geologic age in Thaerodonta-type strophomenides and external shell ornamentation in Strophomena-type strophomenides. In contrast to the strophomenides, there was little evidence for predatory borings in pentamerides and multivariate analyses failed to resolve any trends. Pentamerides may have been unsuitable prey items due to their internal muscle platform structure, which made muscles unavailable to drilling predators.
Borings in Paleozoic brachiopods from northern and eastern Canada represent a combination of post-mortem, parasitic and predatory behaviors, the interactions of which were complex and affected by numerous factors, such as geologic age, brachiopod shell ornamentation and internal skeletal structures. These relationships can be better understood by studying large sample sizes of borings and applying quantitative and multivariate analyses.