Revisiting abnormalities of trilobite Paradoxides davidis from Manuels River, Canada, alongside additional abnormal specimens from Porth-y-rhaw, Wales

Abstract Trilobites, one of the most abundant and diverse Paleozoic groups, often preserve abnormalities on their calcium carbonate exoskeletons. These abnormalities have been characterized by the presence of aberrant circular or oval structures, the partial removal, distortion or addition of segments. Abnormalities are generally attributed to pathologies, genetic complications or injuries. Abnormalities on Paradoxides davidis specimens from Manuels River, Canada (Cambrian: Drumian) were previously attributed to developmental aberrations. This study revisits these abnormalities from Manuels River and describes new abnormal P. davidis specimens from the type locality for the species, Porth-y-rhaw, Wales, UK (Cambrian: Drumian), and argues that these abnormalities resulted from injuries rather than developmental aberration. Analyses of injury location and frequency show an increased concentration towards the posterior. A cannibalistic lifestyle for P. davidis is possible, based on the large size of injuries.