Reconstructing Dunkleosteus terrelli (Placodermi: Arthrodira): A new look for an iconic Devonian predator

Abstract

Dunkleosteus is a widely-recognized prehistoric organism, yet its life appearance, paleobiology, and even basic morphology remain poorly understood. A new reconstruction of D. terrelli is presented here based on examination of complete, threedimensionally mounted dermal skeletons and a review of available paleontological evidence. Despite the post-thoracic body of D. terrelli being poorly known, its morphology and body shape can be constrained based on preserved elements and conserved anatomical patterns seen both within arthrodires and across fishes more broadly. Trunk armor proportions, estimated body length, and the locations of the fin bases suggest D. terrelli had a relatively stout, deep trunk. Its trunk armor is apomorphically deep among arthrodires, resulting in a body shape reminiscent of other pelagic vertebrates (lamnids, thunnins, ichthyosaurs). The anterior trunk is stiffened due to the interlocking ventral shield plates and fused spine restricting lateral motion, and its anatomy suggests extremely large lateral trunk muscles and a well-developed horizontal septum, compatible with thunniform swimming. Body depth is positively allometric in D. terrelli, resembling other arthrodires. Eubrachythoracid arthrodires likely had incomplete lateral lines. The pectoral fin base of Dunkleosteus is located at an extreme anterior position on the body, and the pelvic girdle is unusually small. Arthrodires appear more disparate in body shape than previously assumed, and many taxa may have been well-adapted to active nektonic life, though their rigid dermal armor and generally stocky bodies imply swimming kinematics unlike most living fishes. Many questions about their biology and biomechanics remain unanswered, representing ideal targets for future research.