Helodus, Belantsea, Deltoptychius, Delphyodontos, Obruchevodus, Rhinochimaera, Callorhinchus and Chimaera

Helodus simplex (Agassiz 1838; Late Devonian to Early Permian; 30cm) nests basal to chimaeroids, derived from Isurus. The skull bones are fused together, so estimates in color are provided above for them. Note the tiny premaxillary teeth and multicusped maxillary teeth. The hyomandibular swings anteriorly. and the lacrimal extends further beyond the orbit, as in Callorhinchus. Tabulars appear to be absent. The skull rotates snout down. Note the co-osified cervicals = anterior dorsals to the spine.

Callorhinchus millii (Lacepede 1798, 120cm in length) is the extant elephantfish. Lacrimal and nasal processes anchor the fleshy portion of the sensitive snout for sensing buried prey. The temporal fenestrae are absent. Teeth are reduced to two pair in the upper jaw and one pair in the lower, all flat and broad, not shown above. The dorsal fin spine is erectible.

Obruchevodus griffithi (Grogan et al. 2014; Bear Gulch, Late Carboniferous) is a petalodont close to Belantsea (below) exposing the internal more than the external.

Delphyodontus dacriformes (Lund 1980; Bear Gulch, Late Carbonferous; second specimen, 2.9cm) was named earlier, but considered a finless embryo with a teardrop-shaped body capable of oophagy (eating siblings within the womb). The 'abdominal enlargement' is actually a pair of pectoral fins, as in Obruchevodus and Belantsea.

Belantsea montana (Lund 1989; Early Mississipian, Early Carboniferous; 25 cm in length) is a mid-sized petalodont ratfish. These taxa have giant, fan-like pectoral fins and a small diphycercal tail. The dark spot on the torso is the liver and other internal organs. Morphology and dental similarities indicate convergence with extant queen triggerfish, like Balistes.

Chimaera monstrosa (Linneaus 1758), the extant rabbitfish, a type of ratfish, nests between sharks and sturgeons in the LRT. The quadrate shifts anteriorly to below the orbit. The teeth are transformed and fused to plates and beaks. The large pectoral fins provide propulsion while the tail is reduced.

Deltoptychius armigerus (Morris and Roberts 1862; Traquair 1897; Early to Late Carboniferous; P62092) is known from several specimens. This ratfish has an antorbital fenestra and nests with Chimaera, not with Menaspis, a spiny shark.

Rhinochimaera pacifica (Mitsukuri 1895, 130cm in length) is the extant Pacific spookfish. A long nasal bone greatly extends the rostrum, creating a larger sensory surface, as in sawfish, hammerheds and paddlefish by convergence.

Agassiz L 1838. Recherches Sur Les Poissons Fossiles. Tome III (livr. 11). Imprimérie de Petitpierre, Neuchatel 73-140.

Agassiz L 1848. Nomenclatoris zoologici index universalis: continens nomina systematica classium, ordinum, familiarum et generum animalium omnium, tam viventium quam fossilium, secundum ordinem alphabeticum unicum disposita, adjectis homonymiis plantarum, nec non variis adnotationibus et emendationibus.

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.

Grogan ED, Lund R and Fath M 2014. A new petalodont chondrichthyan from the bear gulch limestone of montana, USA, with reassessment of Netsepoye hawesi and comments on the morphology of holomorphic petalodonts. Paleontological Journal 48 (9): 1003–1014.

de Lacepede BGE 1798. Histoire naturelle des poissons. Plasson, Paris. Vol. 1: 1-8.

Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

Long JA 1995. The rise of fishes. The Johns Hopkins University Press, Baltimore and London.

Lund R 1980. Viviparity and Intrauterine Feeding in a New Holocephalan Fish from the Lower Carboniferous of Montana. Science, New Series 209(4457):687–699.

Lund R 1985. The morphology of Falcatus falcatus (St. John and Worthen) a Mississippian stethacanthid chondrichthyan from the Bear Gulch limestone of Montana. Journal of Vertebrate Paleontology 5:1–19.

Lund R 1989. New petalodonts (Chondrichthyes) from the Uppper Mississippian Bear Gulch limestone (Namurian E2b) of Montana. Journal of Vertebrate Paleontology 9(3):350–369.

Mitsukuri x 1895. On a new genus of the chimaeroid group Hariotta. Dobutsugaku Zasshi, 7 (80): 97–98, Pl. 16.

Morris J and Roberts GE 1862. On the Carboniferous Limestone of Oreton and Farlow, Clee Hills, Shropshire. Quarterly Journal of the Geological Society of London, 18: 94–106.

Patterson C 1965. The phylogeny of the chimaeroids. Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences, 249(757): 101–219.

Patterson C 1968. Menaspis and the Bradyodonts. Nobel Symposium 4: 171–205.

Traquair RH 1897. List of the Fossil fish-remains Occurring in the Bone Bed at Abden, Near Kinghorn, Fifeshire. Proceedings of the Geologists' Association, 15(4):143–145.

wiki/Chimaera
wiki/Symmoriida
wiki/Rhinochimaera
Wike/Obruchevous - not yet posted
wiki//Delphyodontos
wiki/Belantsea
wiki/Deltoptychius
wiki/Callorhinchus
wiki/Helodus