DINICHTHYIDAE NEWBERRY, 1885

Carr, Robert K. & Hlavin, William J., 2010, Two new species of Dunkleosteus Lehman, 1956, from the Ohio Shale Formation (USA, Famennian) and the Kettle Point Formation (Canada, Upper Devonian), and a cladistic analysis of the Eubrachythoraci (Placodermi, Arthrodira), Zoological Journal of the Linnean Society 159 (1), pp. 195-222 : 212-213

FAMILY DINICHTHYIDAE NEWBERRY, 1885

Newberry (1885) erected the family Dinichthyidae for a number of large North American arthrodires. Dunkle & Bungart (1946) recognized two subgroups among the taxa they included as dinichthyids. Their herzeri group consisted of Di. herzeri , Gor. clarki, He. gouldii , and Ho. holdeni . Their terrelli group included Du. terrelli , along with the additional species Dunkleosteus intermedius ( Newberry, 1889) and Dunkleosteus curtis ( Newberry, 1888) . Dunkle & Bungart (1946) based these subgroups on the presence of an obtuse ( herzeri group) vs. an acute cutting edge ( terrelli group) on the inferognathal, and the absence ( herzeri group) vs. the presence ( terrelli group) of a parasphenoid–anterior superognathal plate contact. Such subdivisions were an attempt to uncover the phylogenetic relationships among the Dinichthyidae ; however, it can now be shown that these putative subgroups are not closely related (i.e. polyphyletic), although independently they may each represent a natural group. Hlavin (1976) subsequently synonymized Du. intermedius , Du. curtis , and Dunkleosteus prentis - clarki ( Claypole, 1896) with Du. terrelli (see also Denison, 1978). Denison (1978) included in the family Dinichthyidae , Dinichthys , Dunkleosteus , Eastmanosteus , Gorgonichthys , Hadrosteus , Heintzichthys , Holdenius , Hussakofia , and Kiangyousteus . Carr (1991) noted that He. gouldii and Gor. clarki are related more closely to some members of the Aspinothoracidi than to either Dunkleosteus or Eastmanosteus . Based on the present analysis, Di. herzeri and Ho. holdeni are also members of the Aspinothoracidi. Therefore, the distinction noted by Dunkle & Bungart (1946) is valid (i.e. the herzeri and terrelli groups represent members of distinct clades), although members of the herzeri group are assigned to the Aspinothoracidi. It also appears that the herzeri group members may belong to a more inclusive clade within the Aspinothoracidi (node 8; Fig. 9 ). The terrelli group has indeed collapsed with the synonymy of the Dunkleosteus species. The remaining taxon ( Du. terrelli ) is part of a larger monophyletic family, the Dunkleosteidae (node 11; Fig. 9B ).

An analysis of the described material ( Newberry, 1868; Hlavin, 1976) for Di. herzeri suggests that this species is the sister taxon for the clade (( Gor. clarki , Ha. rapax ) He. gouldii ) ( Fig. 9 ). These relationships are consistent among all the analyses conducted during the current study ( Fig. 9 ); however, a more detailed resolution of the phylogenetic relationships of Di. herzeri among the Aspinothoracidi (node 8; Fig. 9 ) should require a complete analysis of the Aspinothoracidi. Dinichthys herzeri shares with aspinothoracid arthrodires a reduction of the occipital thickening of the skull roof, and the modification of the paired pits and posterior process on the nuchal plate ( Fig. 1A ).

The position of Di. herzeri among the Aspinothoracidi requires the reassignment of the Dinichthyidae (node 13; Fig. 9B ) to the Aspinothoracidi (node 8; Fig. 9 ). This leaves the family with only a single species ( Di. herzeri ). This assessment remains tentative pending a more inclusive and detailed analysis of the Aspinothoracidi. However, the reassignment of the family Dinichthyidae comb. nov. leaves its former member genera ( Dunkleosteus , Eastmanosteus , Hadrosteus , Hussakofia , and Kiangyousteus ) in an unnamed clade, among which Dunkleosteus is the best known and is the type genus for the family Dunkleosteidae . Hadrosteus rapax is a member of Aspinothoracidi united with Gor. clarki . Hussakofia minor ( Newberry, 1878) is known only from fragmentary material: only a nuchal plate, the form of which suggests a brachythoracid level of organization, and an inferognathal plate that possesses two cusps (character 89, state 1), suggesting a closer relationship with either Dunkleosteus or Golshanichthys . Kiangyousteus yohii is too poorly known to be evaluated at the present time, and is referred to Pachyosteomorphi incertae sedis. The remaining former dinichthyid genera include Eastmanosteus , Hussakofia , Westralichthys , and Golshanichthys . These taxa are united with Dunkleosteus (node 9; Fig. 9 ) in the Dunkleosteidae (node 11; Fig. 9B ).

Figures

Figure 1. Dinichthys herzeri. A, AMNH 81 (holotype), incomplete nuchal plate in internal view. B, AMNH 73 (paratype), left inferognathal plate in lateral view. C, AMNH 34, left anterior superognathal in lateral view. D, AMNH 33, right posterior superognathal in lateral view. Reconstruction of six denticles in the posterior tooth row based on CMNH 7257. Drawings reproduced from Hlavin, 1976. Scale bars equal 3 cm.

Figure 9. A, strict consensus tree based on 98 characters and 23 taxa derived from PAUP* (consensus tree length, TL = 246; consistency index, CI = 0.498; retention index, RI = 0.502; and Rohlf’s CI = 0.708; consensus based on six trees, TL = 237, CI = 0.498, and RI = 0.537). B, strict consensus tree based on 98 characters and 22 taxa (excluding Kiangyousteus yohii, consensus TL = 237, CI = 0.498, RI = 0.535, and Rohlf’s CI = 0.993; consensus based on three trees, TL = 237, CI = 0.498, and RI = 0.535). Named nodes: node 1, Brachythoraci; node 4, Eubrachythoraci; node 5, Pachyosteomorphi; node 6, Coccosteomorphi; node 8, Aspinothoracidi; node 9, Dunkleosteus; node 10, Panxiosteidae; node 11, Dunkleosteidae; node 12, Dunkleosteoidea; and node 13, Dinichthyidae. *Character scores for Homostius compiled for the Baltic species sensu Heintz, 1934. **Scores based on Camuropiscis concinnus and Camuropiscis laidlawi.