Heintzichthys gouldii

The giant placoderm Heintzichthys gouldii (not to be confused with Heintzosteus) menaces the primitive shark, Stethacanthus resistens, in late Devonian Cleveland.
H. gouldii was slightly smaller than its more infamous contemporary, Dunkleosteus terrelli. Apparently, it had eyes the size of watermelons, suggesting it may have been nocturnal.