Short Guide To Solnhofen Fishes

[oilshale]

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.

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).

Belonostomus münsteri from Painten, Germany

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.

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.

Aspidorhynchus, showing the long upper and very short lower 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.

Edited February 4, 2011 by oilshale

[oilshale]

This is a juvenile Belonostomus from the Painten region, also Kimmeridgian and not Tithonian. Size is a meager 5cm; it's the smallest one I've ever seen!

Edited February 4, 2011 by oilshale

[Auspex]

The upper and lower jaws on the little one appear to be nearly the same length; possibly the adult morphology is something they "grow into"?

[Bill]

"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 jaw".

Edited February 5, 2011 by Bill

[Auspex]

Here's what I'm on about:

The jaws on little one seem to be closer to equal length than those on the big one.

[Bill]

Yes, sorry, .I see what you mean now.