Lund 1982 described an eel-like specimen with almost no scales
Harpagofututor volsellorhinus (Figs. 1, 3, 5), as a type of bradyodont shark.
the large reptile tree (LRT, 1782+ taxa) Harpagofututor nested with another eel-like bony fish close to sharks with no scales, Gymnothorax (Figs. 2, 4). Both were derived from the traditional chimaera, Gregorius (Fig. 6). and the scaleless incertae sedis, Prohalecites. These nest as basalmost bony fish in the LRT, derived from the shark, Hybodus. Lund did not mention these taxa in his paper on Harpagofututor.
From the Lunds 1982 abstract:
“A new chondrenchelyoid bradyodont, Harpagofututor volsellorhinus is described from the Namurian Bear Gulch limestone beds, Bear Gulch member of the Heath Formation, of Montana. It has a bladelike body form with a low, continuous dorsal fin, segmental vertebral arcualia, and a biserial archipterygial pectoral fin, as does Chondrenchelys problematica. There are two paired flat upper tooth plates, and a symphysial plus two paired crushing lower tooth plates. Males have large paired, distally biramous ethmoid claspers.”
the much larger and more derived, Helicoprion vessonowi (Figs. 5; Karpinsky 1899; Bendix-Almgreen 1966; Tapanila et al. 2013; Permian, 290-270 mya; possibly 12m in length) had a symphysial (central) tooth whorl and two lateral tooth plates arising from the dentary. In the more primitive, Harpagofututor, those three tooth plates arose one in front, two in back. In Helicoprion the two now toothless plates support the much larger central tooth whorl. The other elements resemble Harpagofututor to such an extent that a relationship seems to be present, reducing the mystery surrounding Helicoprion. Harpagofututor was not mentioned in the Tapanila et al. 2013 redecription of Helicoprion. They referred Helicoprion to the Euchondrocephali, which includes Gregorius (Fig. 6).
The facial claspers of a male Harpagofututor
(Fig. 5) are similar to, but different from similar additional nasal bones arising from ratfish.
The present hypothesis of interrelationships appears to be a novel one.
If there are similar prior hypotheses, please bring them to my attention so I can promote them.
Bendix-Almgreen SE 1966. New investigations on Helicoprion from the Phosphoria Formation of south-east Idaho, USA. Biol. Skrifter udgivet af det Kongelige Danske Videnskabernes Selskab 14, 1–54.
Lund R 1982. Harpagofututor volsellorhinus new genus and species (Chondrichthyes, Chondrenchelyiformes (from the Namurian Bear Gulch limestone, Chondrenchelys problematica Traquair (Visean), and their sexual dimorphism. Journal of Paleontology 56(4):938–958.
Tapanila L et al. (6 co-authors) 2013. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helcoprions. Biology Letters 9, 20130057, http://dx.doi.org/10.1098/rsbl.2013.0057