''Asthenoceras'' is a genus of ammonoid from the Middle Jurassic (Lower

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.3 Ma to around 168.3 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonian Age. Stratig ...

) with dwarfish, evolute, smooth, compressed, discoidal, strongly keeled shell. ''Asthenoceras'' belongs to the

Sonniniidae Sonniniidae is a diverse family of Middle Jurassic ammonites ranging from those with stout evolute shells to those whose shells are sharply rimmed, oxyconic. The keel, which runs along the middle of the venter, is typically hollow. Sutures vary f ...

and may be a subgenus of the Lower Jurassic (Upper

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarcian ...

) ''

Grammoceras ''Grammoceras'' is an extinct genus of ammonite found in Yorks Ravenscar, England, from Jurassic period sediments. Its overall distribution is fairly worldwide. ''Grammoceras'' has a thin, discoidally evolute shell with simple, gently sigmoid ...

''.

References

* Ammonitida genera Sonniniidae Jurassic ammonites Fossils of Morocco Bajocian life {{Ammonitina-stub