New information on Titanichthys (Placodermi: Arthrodira) from the Cleveland shale (upper devonian) of Ohio, USA

The placoderm (Titanichthys) from the Late Devonian (Famennian) is based on incomplete and fragmentary specimens that have hindered understanding of its overall anatomy and phylogenetic relationships. A new, nearly complete, articulated specimen from the Upper Devonian Cleveland Shale provides new information about the previously undescribed rostral, postmarginal, postsuborbital, submarginal, posterior superognathal plates, and the nasal capsule. A revised diagnosis is provided for the genus. Three new diagnostic characters are identified including a transversely elliptical rostral plate that does not contact adjacent plates, a reduced posterior superognathal, and a median dorsal plate that inserts into the posterior dorsal lateral plate. The first comprehensive phylogenetic analysis of (Titanichthys) indicates that the genus is a basal aspinothoracid arthrodire closely related to the enigmatic taxa (Bungartius) and (Tafilalichthys).晚泥盆世（Late Devonian）法门期（Famennian）的泰坦鱼属（Titanichthys，隶属于盾皮鱼（placoderm）），其相关研究长期受制于不完整且碎片化的标本，极大阻碍了学界对其整体解剖结构与系统发育关系的认知。本次研究报道一件采自上泥盆统克利夫兰页岩（Cleveland Shale）的全新近乎完整且关联保存的标本，为此前尚未被描述的吻板（rostral）、缘后板（postmarginal）、眶后下板（postsuborbital）、亚缘板（submarginal）、后上颌板（posterior superognathal plates）以及鼻囊（nasal capsule）提供了全新的研究资料。本研究为该属提供了修订后的鉴别诊断，共识别出三项新的鉴别性状：其一为横椭圆形且不与相邻骨板接触的吻板，其二为退化的后上颌板，其三为嵌入后背侧板（posterior dorsal lateral plate）的中背板（median dorsal plate）。针对泰坦鱼属（Titanichthys）的首次全面系统发育分析显示，该属属于基干无棘胸节类节甲鱼（basal aspinothoracid arthrodire），与疑难类群邦干鱼属（Bungartius）和塔菲拉利鱼属（Tafilalichthys）亲缘关系密切。