ITERATIVE EVOLUTION OF FUSED DENTICLES (SPATULATE FORMS) AMONG OZARKODINID CONODONTS IN THE AFTERMATH OF SUCCESSIVE SILURIAN BIOGEOCHEMICAL EVENTS

Several species of Silurian conodonts assigned to the genus Ozarkodina exhibit fused denticulation either immediately above the basal cavity, or extending completely to the dorsal (posterior) end of P₁ elements. Specifically, Ozarkodina bohemica longa, Ozarkodina bohemica bohemica, Ozarkodina snajdri, Ozarkodina crispa, and to a lesser extent, Ozarkodina sagitta rhenana all develop some degree of denticle fusion during the Silurian. As global biogeochemical studies begin to provide better temporal resolution between inter-related biological and geochemical events during this interval of Earth history, it has become clear that the three intervals of the Silurian during which ozarkodinid species developed fused denticles are not random, but rather occurred in the immediate aftermath of major biogeochemical events that took place during the Wenlock and Ludlow epochs (Ireviken, Mulde, and Lau events).

At this point, it remains entirely unclear what the relationship was, if any, between these biogeochemical events and the development of fused denticulation in some ozarkodinid species. However, the context of the biogeochemical event intervals presents several potential causal mechanisms for these changes in morphology. Firstly, they could be a response to altered predator-prey interactions caused by changes in prey availability within the lower tiers of the food chain during the disaster intervals of these events. They could be the result of geochemically induced malformations in the growth of P₁ elements in these conodonts that turned out to be ecologically advantageous. They could be the result of altered seawater chemistry affecting the conodont animals’ ability to mineralize their elements. Regardless of any possible causal mechanism(s), it seems very likely that this phenomenon would not be restricted solely to the Silurian Period and this specific group of conodonts. Other intervals of Earth history likely contain similar biogeochemical events that may have similarly affected other evolutionary lineages, and efforts should be made to bring such evidence to light.