Two middle Cambrian diceratocephalid trilobites, Cyclolorenzella convexa and Diceratocephalus cornutus, from Korea: development and functional morphology

摘要

Silicified sclerites of the latest middle Cambrian trilobites, Cyclolorenzella convexa and Diceratocephalus cornutus, have been recovered from the Sesong Formation, Korea. Their morphological similarity and stratigraphic occurrences suggest that D. cornutus is a descendant of C. convexa. The ontogenies of both trilobites demonstrate that a pair of long frontal horns in the cephalon of D. cornutus is an evolutionarily novel structure. It is inferred that redeployment of some pre-existing regulatory gene played a significant role in constructing the frontal horns of D. cornutus. The frontal horns may have been a defensive structure to deter predators. The facial suture of D. cornutus, which extends onto the frontal horns and splits them into the dorsal and ventral halves, was a solution to enable easier forward egression during ecdysis.