NEW INFORMATION ON TITANICHTHYS (PLACODERMI: ARTHRODIRA) FROM THE CLEVELAND SHALE MEMBER OF THE OHIO SHALE FORMATION (FAMENNIAN) OF OHIO, USA
The new, mostly complete specimen is articulated and includes several cranial plates previously undescribed in American Titanichthys specimens; these include the rostral, postmarginal, posterior superognathal, postsuborbital and submarginal plates, with a possible fragment of a sclerotic ring. The anterior border of median dorsal plate preserves a narrow, deep embayment in addition to the normal emargination seen in this taxon and other derived arthrodires. This deep embayment has not been previously observed in Titanichthys or other related taxa, and thus may represent an autapomorphy that can only be confirmed by the discovery of new specimens.
The new phylogenetic analysis indicates a close relationship of Titanichthys with Heintzichthys, also found in the Cleveland Shale, and has confirmed Titanichthys position within the aspinothoracid arthrodires.