Ecological interactions between rhipidomella (Orthides, Brachiopoda) and its endoskeletobionts and predators from the Middle Devonian Dundee Formation of Ohio, United States

Only the small (2.0 ± 0 . 1 cm) orthide brachiopod Rhipidomella in the Middle Devonian Dundee Formation exposed at Whitehouse Quarry, Ohio, preserves evidence of interactions with endoskeletobionts and predators (39.6%, n = 48), as opposed to the slightly larger atrypides, spiriferides, and stropheodonts (n = 245). All traces of prédation and boring by other organisms are lacking on such larger brachiopods as strophomenides and spiriferides, which are more often encrusted in Devonian localities of North America—the Silica Shale of Ohio, Hamilton Group of New York, and Cedar Valley Limestone of Iowa. Punctate shells of Rhipidomella preserve interactions with endoskeletobionts and predators, phenomena less common for punctate brachiopods. All traces on Rhipidomella were preserved as endoskeletobionts; if calcified encrusters were present, they likely were lost postmortem. Several Rhipidomella individuals bear partially repaired grooves from parasitic interactions with sinuous, boring organisms, attributed to ctenostome bryozoans. These parasites bored into the shell along the commissure, likely benefiting from the inhalant and exhalant currents produced by the brachiopod, and in some cases, expanded away from the commissure following the host's death. The straight, U-shaped borings in one Rhipidomella specimen with boreholes are similar in morphology to Caulostrepsis traces that occurred with their tubes opening along the margins of a modern brachiopod. Other endoskeletobiont traces likely formed on the postmortem shells of Rhipidomella. Prédation repair scars are present on two specimens, indicating the presence of predators and the survival of some Rhipidomella individuals from durophagy. No specimens contain evidence of drilling predators.