Temporal range: Eifelian-Lower Givetian
Protitanichthys is a genus of comparatively large coccosteid arthrodire placoderm from the Middle Devonian of the eastern United States. Fossils are found primarily in the Eifelian-epoch aged Delaware Limestone of Ohio, and the Lower Givetian-aged Rockport Quarry of Michigan
Protitanichthys is very similar to other coccosteids, though the skull is proportionally narrower, and the orbits are comparatively smaller. As mentioned earlier, species are quite large for coccosteids, surpassed only in size by the Old World genus, Livosteus.
As the specific name suggests, numerous scrappy remains of this species are found in the Lower-Givetian Rockport Quarry in Michigan. Denison (1978) questions the status of P. rockportensis being distinct from P. fossatus, as there are very few differences between the two, aside from chronological and geographical differences.