Biomechanical assessment and the fossil record suggest a sensory function in the anterior glabellar and genal spines in Ordovician raphiophorid trilobites

Abstract

Raphiophorid trilobites were small, abundant, and diverse Ordovician trilobites. One of the most remarkable features of these blind trilobites was a spine projecting from the anterior part of the glabella. The discovery of rows of Ampyx in the Ordovician of Morocco suggests that the function of this structure may have been related either to enhancing hydrodynamics or to acting as a sensory organ in conjunction with the genal spines. However our results using computational fluid dynamics (CFD) have shown that the spine did not provide any hydrodynamic advantage to these animals. Instead, the shape of the cephalon and body alone was sufficient to prevent them from being dislodged from the seafloor by water currents. The CFD simulations combined with new evidence from the fossil record, of various raphiophorid cuticular structures, suggest that the anterior glabellar and genal spines functioned as a sensory organ. This adaptation likely helped these blind trilobites interact with conspecifics and maintain their orientation in their environment.