Debeerius, Caseodus, Chondrenchelys, Heteropetalus, Harpagofututor and Edestus

Debeerius ellefseni (Grogan and Lund 2000; Mississipian, 320 mya) was originally considered intermediate betweeen sharks and ratfish, but here nests basal to the buzz saw 'shark' clade that includes Helicoprion (below).

Heteropetalus elegantulus (Lund 1977; Bear Gulch Fm., Mississipian, 320mya)is a sister to Harpagofututor and thus basal to the clade that produced circular-saw-toothed Helicoprion. It retains a tiny dorsal spine, but it has become eel-like overall. Widely considered an aberrant shark, here it bridges the transition from ratfish to buzz tooth fish.

Chondrenchelys problematica (Traquair 1888, Finarelli and Coates 2014; Viséan, Early Carboniferous) nests with Heteropetalus, only longer. These are eel-like holocephalians.

Harpagofututor female and male skulls from Lund 1982

Harpagofututor volsellorhinus (Lund 1982; Viséan, Late Carboniferous; 17cm) was originally considered a bradyodont shark from the Bear Gulch Formation with sexual dimorphism (claspers on the nasal of the male). Here it nests between Gregorius and Gymnothorax. Lund did not mention these taxa in his paper on Harpagofututor. Four embryos are found in one female specimen.

Caseodus basalis (Zangrel 1981, Carboniferous to Early Triassic, 1.5m) was considered a member of the Eugeneodontida, the clade of chondrichthyans with tooth whorls. This specimen has tooth whorls at its jaw tips. Note the large eyes followed immediately by the hyomandibular, migrating the jaw joint below the orbit. Gray arrow points to the occipital region of the skull.

Edestus heinrichi (Leidy 1856; Tapanila et al. 2020; FMNH PF2204; 25cm skull length; Pennsylvanian)is an extinct scissor shark with medial dentition, small eyes and a sharp rostrum, similar to, but distinct from Helicoprion.

Helicoprion vessonowi (Karpinsky 1899; Bendix-Almgreen SE 1966; Tapanila et al. 2013 Permian, 290-270 mya; possibly 12m in length; above) is known from tooth whorls, palate and jaw elements that nearly match those of the much smaller Harpagofututor. In Helicoprion the posterior pair of tooth plates migrate to both sides of the medial tooth for support.

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.

Finarelli JA and Coates MI 2014. Chondrenchelys problematica (Traquair, 1888) redescribed: A Lower Carboniferous, eel-like holocephalan from Scotland. Article in Earth and Environmental Science Transactions of the Royal Society of Edinburgh

.Grogan ED and Lund R 2000. Debeerius ellefseni (Fam. Nov.,Gen. Nov., Spec Nov.), an autodiastylic chondrichthyan from the Misssissippian Bear Gulch limestone of Montana (USA), the relationships of the Chondrichthyes, and comments on gnathostome evolution. Journal of Morphology 243:219–245.

Leidy J 1856. Indications of five species, with two new genera, of extinct fishes. Proc Acad Nat Sci Philadelphia 7:414.

Lund R 1977. A new petalodont (Chondrichthyes, Bradyodonti) from the Upper Mississippian of Montana. Annals of Carnegie Museum 46 article 10:129–155.

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

Tapanila L, Priuitt J, Wilga CD and Pradel A 2020. Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition. The Anatomical Record 303:363–376.

Traquair RH 1888a. Further notes on Carboniferous Selachii. Proceedings of the Royal Physical Society of Edinburgh 9, 349–61.

Traquair RH 1888b. Further notes on Carboniferous Selachii. Geological Magazine 5, 101–04.

Zangerl R 1981. Chondrichthyes I: Paleozoic Elasmobranchii, In: Schultze, H.P.
(ed.), Handbook of Paleoichthyology 3A, Gustav Fischer Verlag, 115 p.

wiki/Harpagofututor
wiki/Euchondrocephali
wiki/Debeerius
wiki/Edestus
wiki/Chondrenchelys
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wiki/Caseodus