Megalytoceratinae is a subfamily of lytoceratids

ammonites Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

consisting of planulate forms, i.e. those with moderately evolute compressed shells with bluntly rounded venters, in which the outer whorls become smooth and sutures tend to resemble those of the

Perisphinctidae Perisphinctidae is a family of Middle and Upper Jurassic discoidal ammonites in the order Ammonitida. They have a shell morphology that is mostly evolute, typically with biplicate, simple, or triplicate ribbing. Large forms have simple aperture ...

. The family includes three genera, '' Megalytoceras'', and '' Metrolytoceras'', from the Middle Bajocian of England, '' Perilytoceras'' from the

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 ...

and a fourth possible member, '' Asapholytoceras'', from the Toacian of southeastern Europe.

References

*W.J.Arkell, B.Kummel, & C.W.Wright 1957. Mesozoic Ammonoidea, Treatise on Invertebrate Paleontology, Part L Ammonoidea. R.C.Moore, (ed). Jurassic ammonites Toarcian first appearances Middle Jurassic extinctions Lytoceratidae {{ammonitida-stub