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Taxonomy from Fossilworks. From Ebert 2014, p. 39: "Belonostomus sphyraenoides Agassiz, 1844 is known only from the Eichstätt basin. Belonostomus is very rare in the Plattenkalk basin of Eichstätt and as far as I know, all specimens belong to B. sphyraenoides. The Plattenkalk of Eichstätt is dated as eigeltingense β horizon of the Tithonian (Schweigert et al. 2013). Belonostomus sphyraenoides has about 71 vertebrae and 71 lateral line scales." References: Agassiz, L. (1833-1844): Recherches sur les Poissons Fossiles.- 5 vols., 1420 pp. 396pls., with supplements. Petitpierre, Neuchâtel et Soleure. Ebert, Martin (2014) The genus Belonostomus Agassiz, 1834 (Neopterygii, Aspidorhynchiformes) in the late Jurassic of the Solnhofen Archipelago, with a focus on Belonostomus kochii Münster, 1836 from Ettling (Germany). Archaeopteryx 32: 15-43.

Quote from Ebert 2014, p. 16-17: “The genus Belonostomus Agassiz, 1834b is one of four genera of the extinct family Aspidorhynchidae Nicholson & Lydekker 1889. The other three are the type genus Aspidorhynchus Agassiz, 1833 from mid to late Jurassic marine deposits of the Tethys (Cuba, France, Germany, Great Britain), Vinctifer Jordan, 1919 from Cretaceous marine deposits of the Gondwana coasts (Antarctica, Argentina, Australia, Brazil, Columbia, Equatorial Guinea, Mexico and Venezuela) and Richmondichthys Bartholomai, 2004 from marine deposits of the Cretaceous (Albian) of Queensland (Australia). The genus Belonostomus is widespread, ranging from the late Jurassic (Kimmeridgian to Tithonian of England, France and Germany) to the Cretaceous (England, Germany, Italy, Lebanon, North and South America) and maybe even up to the Paleocene…” Diagnosis of the genus (amended from Brito 1997 in Ebert 2014, p. 22): "A very slender and elongated Aspidorhynchidae, with a maximum depth (MD) of about 6-9% of standard length (SL). The cranium is also slender and elongate with both jaws of great length. The main characteristic feature is an elongated predentary, which is nearly as long as the dentary. A supramaxilla does not exist. The maxilla is pointed at the ends with a laterally expanded lamella at the dorsal border. Ganoin on the scales is present. There are three dorsoventrally elongated flank scales in the middle of the body, of which the median one is the lateral line scale, which is two to three times higher than long. All fins are reduced in size and have fewer rays than in other members of Aspidorhynchidae." Brito (1997, p. 743-744) mentions a new species of the genus Belonostomus (Belonostomus sp. " 3 ") from the quarry Tlayúa without giving an official name. Identified as Belonostomus sp. by oilshale using Brito, 1997. References: Agassiz L. (1834) Abgerissene Bemerkungen über fossile Fische.- Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde, pp. 379-390. Brito P. M. (1997) Révision des Aspidorhynchidae (Pisces, Actinopterygii) du Mésozoïque : ostéologie, relations phylogénétiques, données environnementales et biogéographiques. Geodiversitas 19 (4): 681-772. g1997n4a2.pdf (mnhn.fr) Espinosa-Arrubarrena, L. and Alvarado-Ortega, J. (2010) Field trip to the Tlayúa quarry. Gonzalez-Rodriguez, K. and Arratia, G. (eds.), Fifth International Meeting of Mesozoic Fishes-Global Diversity and Evolution. Abstract Book & Field Guides. Pachua, Cinecia al Dia, 19:93-113. Ebert, Martin (2014) The genus Belonostomus Agassiz, 1834 (Neopterygii, Aspidorhynchiformes) in the late Jurassic of the Solnhofen Archipelago, with a focus on Belonostomus kochii Münster, 1836 from Ettling (Germany). Archaeopteryx 32: 15-43; Eichstätt.

Belonostomus together with Aspidorhynchus and Vinctifer belongs to the Aspidorhynchidae. Belonostomus and other members of the extinct Aspidorhynchidae family are sometimes called "Needle Fishes". Although the Aspidorhynchidae would have looked superficially similar to the present day gar or a scaled-down version of a modern swordfish, its closest living relative is actually the bowfin. Even the rather similar looking Rhynchodercetis, a fish from the Cretaceous of Lebanon and Morocco, is not related to Aspidorhynchus and Belonostomus. There are two forms described: Belonostomus muensteri Agassiz 1837 and Belonostomus tenuirostris A. Wagner, 1863, the even rarer and above all much smaller representative from the locality Zandt. The species name tenuirostris refers to its tiny rostrum. Whereas the genus Aspidorhynchus (meaning "shield snout") is rather common in the Solnhofen Formation (lower Tithonian, Malm zeta 2a and b, 147mio), the genus Belonostomus (meaning “big long mouth”) is a scarcity. Only in the Daiting area, its marginal outcrop, a larger number of those fishes were recovered. The Daiting deposits are slightly younger and belong to the Mörnsheim Formation (Lower Tithonian, Malm zeta 3, 148mio). This Belonostomus here comes from Painten and is somewhat older (Kimmeridgian, Malm epsilon, 151mio). Similar in body shape to Aspidorhynchus, Belonostomus was also a slender, fast-swimming fish with its fins set far back on the body, like those of a pike. Fish with this body shape generally feed by darting out from ambush and grasping other fish by surprise. Belonostomus is characterized by a ganoid scale covering with much deepened scales along the flank, by an elongate fusiform body and head with long slender snout, and by an externally symmetrical tail. Belonostomus muensteri Agassiz, 1837 reached only a size of 30cm (1ft.), so it was the pocket size version of Aspidorhynchus. Whereas Aspidorhynchus has an upper jaw that was longer than the lower jaw and ended in a toothless spike, the lower yaw of Belonostomus was nearly as long as the upper yaw. This rostrum is a bit of a mystery. It is hard to imagine Belonostomus attacking other fish without spearing them even by accident! Their slender body profile and the fact that the upper jaw bones were immobile preventing the fish from inhaling their prey, suggest that Belonostomus was designed to be a predator. Fossil stomach remains of other fish have been found in specimens of Belonostomus. References: Ebert, M. (2014) The genus Belonostomus Agassiz, 1834 (Neopterygii, Aspidorhynchiformes) in the late Jurassic of the Solnhofen Archipelago, with a focus on Belonostomus kochii Münster,1836 from Ettling (Germany). Archaeopteryx 32: 15-43.