Belonostomus tenuirostris (Agassiz, 1833)

Taxonomy

Kingdom: Animalia
Phylum: Chordata
Class: Actinopteri Cope 1871
Order: Aspidorhynchiformes Bleeker 1859
Family: Aspidorhynchidae Bleeker 1859
Genus: Belonostomus
Species: Belonostomus tenuirostris
Author Citation (Agassiz, 1833)

Geological Time Scale

Eon: Phanerozoic
Era: Mesozoic
Period: Jurassic
Sub Period: None
Epoch: Late
International Age: Kimmeridgian

Stratigraphy

Weissjura Group
Painten Formation

Biostratigraphy

Ulmense Subzone
rebouletianum

Provenance

Acquired by: Purchase/Trade

Dimensions

Length: 33 cm

Location

Rygol Quarry
Painten
Bavaria
Germany

• belonostomus
• fish
• jurassic
• kimmeridgian
• painten
• painten formation
• tff-oilshale-ch2

Comments

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.