Healed injury in a nektobenthic trilobite: “Octopus-like” predatory style in Middle Ordovician?

Abstract

The Lower Paleozoic sediments of the Barrandian area are globally renowned as a classical example of well-preserved skeletal marine fauna, including abundant remains of trilobites. Several tens of morphologically anomalous exoskeletons of trilobites have been collected and documented from Cambrian to Devonian clastic sediments and carbonates. One of them, an exceptionally well preserved, articulated and partly enrolled exoskeleton of the Ordovician nektobenthic trilobite Parabarrandia bohemica (NOVÁK, 1884) exhibits a prominent palaeopathological anomaly in its pygidium. We interpret this anomaly as a healed traumatic injury and attribute this damage to a failed predatory attack. The subsequently healed injury is classified as the ichnogenus Oichnus BROMLEY, 1981. The structure on the pygidium is strongly reminiscent of injuries caused by octopods and a large cephalopod is proposed as a potential durophagous predator responsible for the herein described trilobite injury. However, an attack from an unknown arthropod while the trilobite was in a soft-shelled stage cannot be excluded.