Anisoceratidae is an extinct

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of heteromorph

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) ...

which belong to the Ancyloceratina superfamily

Turrilitoidea Turrilitoidea is a diverse superfamily of Cretaceous ammonites generally considered as heteromorphic and commonly included in the suborder Ancyloceratina. Shells of this diverse group do not coil planospirally, as typical for most ammonitida, am ...

. Members of the family range is from the lower Albian to the upper

Turonian The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by t ...

. The family is possibly derived from a member of the

Hamitidae ''Hamites'' (":wikt:Hamites, hook-like") is a genus of heteromorph ammonite that evolved late in the Aptian stage of the Early Cretaceous and lasted into the Cenomanian stage of the Late Cretaceous. The genus is almost certainly paraphyletic but ...

Morphology

Anisoceratid shells begin as an irregular helical spiral which typically becomes confined to a single plane with growth. This is usually followed by at least a single straight shaft. Ribs and tubercles are common features.

History and classification

Older classifications, since first publication of Part L of the

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...

, include the Anisoceratidae in the suborder Ancyloceratina (within the Turrilitoidea). Subsequent study, e.g. Beznosov & Mikhailova 1983, has suggested that the Turrilitoidea, including the Anisoceratidae, have a different phylogeny from the true Ancyloceratina, resulting in their occasional reassignment to a separate suborder, the

Turrilitina Turrilitina is a proposed suborder of Cretaceous heteromorph ammonoid cephalopods derived from the Lytoceratidae in the Hauterivian stage of the Lower Cretaceous that would include the superfamilies Turrilitoidea, Ptychoceratoidea, and Scapha ...

, however this classification is not widely followed.

References

* *Beznosov & Mikhailova 1983 referenced in A. Mikhailova and E. Yu. Baraboshkin, 2009. The Evolution of the Heteromorph and Monomorph Early Cretaceous Ammonites of the Suborder Ancyloceratina Wiedmann. Paleontological Journal, Vol. 43, No. 5, 2009.
The Paleobiology Database Anisoceratidae entry
Cretaceous ammonites Ammonitida families Turrilitoidea Albian first appearances Turonian extinctions {{Ammonitida-stub