Pearl formation in an Early Cretaceous belemnite

Abstract

Many aspects of the paleobiology and biomineralization of belemnites, the most common fossil coleoid cephalopods of the Mesozoic, are still unclear. Here, we describe a pearl from an Early Cretaceous belemnite rostrum (Duvalia emerici) using high-resolution micro-CT imaging. After initial formation of a free pearl within the soft tissue, the pearl was fused to the rostrum and later overgrown by rostrum increments, thereby forming a blister pearl. The contact zone of the pearl with the rostrum shows resorption and deformation of earlier rostrum increments. Formation of a free pearl inside the soft tissue of the belemnite demonstrates a relatively thick (min. 5.6 mm) tissue layer surrounding the rostrum in this species. Our data show that classification of paleopathologies based on external features alone might lead to false inferences of formation mechanisms.