Structure, Growth and Histology of Gnathal Elements in Dunkleosteus (Arthrodira, Placodermi), with a Description of a New Species from the Famennian (Upper Devonian) of the Tver Region (North-Western Russia)

A new species of Dunkleosteus, D. tuderensis sp. nov., is named based on an infragnathal from the Famennian Tver Region, Russia. CT scanning holotype revealed two high-density bony constituents comparable in position and interrelations to components described for coccosteomorph arthrodires, supported by presence at least clusters large vascular canals marking separate arterial supplies. Coccosteomorph dunkleosteid pachyosteomorphs exhibit similar growth patterns including labio-basal depositions vascularized bone infragnathals basally supragnathals. In contrast coccosteomorphs, reinforcement occlusal margins occurred via formation dense osteonal bone, parallel with resorption forming extensive lingual fossae. Active remodeling proceeded without a complete reworking primary structure original arrangement canals. Due inconsistent anatomical terminology gnathal elements revised suggested terms are introduced.