Xenoceltitidae are evolute, generally ribbed, upper Lower

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

Ceratitida Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian, the exception being the phylloceratids which gave rise to the great diversity of post Triassic ammoni ...

with ceratitic or goniatitic sutures; formerly included in the Noritaceae but now placed in the Xenodiscaceae. The Xenoceltitidae are derived from the

Ophiceratidae The Ophiceratidae is a family in the ammonoid order Ceratitida from the Lower Triassic, previously included in the Otocerataceae but now placed in the Noritiaceae as revised. The Ophiceratidae produced sepenticones with compressed elliptical who ...

References

* Arkell et al. 1957; Mesozoic Ammonoidea, Treatise on Invertebrate Paleontology, Part L, Ammonoiea; Geological Society of America
The Paleobiology Database
Xenodiscoidea Ceratitida families Early Triassic first appearances Early Triassic extinctions {{Ceratitida-stub