Clydonitoidea, formerly Clydonitaceae, is a superfamily in the

ammonoid 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) ...

cephalopod order

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 ...

characterized by generally costate and turberculate shells with smooth, grooved, or keeled venters and sutures that are commonly ceratitic or ammonitic but goniatic in a few offshoots.

Taxonomy

Clydonitoidea unites 14 families (Arkell et al. 1962) (12 in Kummel 1952) derived from two ancestral stocks within, the Arpaditidae and the

Trachyceratidae The Trachyceratidae is an extinct family of ceratitid ammonoid cephalopods. The Trachyceratidae makes up part of the superfamily Trachyceratoidea along with such families as the Buchitidae, Distichitidae, Dronovitidae and Noridiscitidae. ...

, which are derived from the

Ceratitaceae Ceratitoidea, formerly Ceratitaceae, is an ammonite superfamily in order Ceratitida characterized in general by highly ornamented or tuberculate shells with ceratitic sutures that may become goniatitic or ammonitic in some offshoots. (Arkell ' ...

. The Trachycerataceae, Haug 1894, used by Kummel, 1952 and more recently by Tozer, was originally equivalent to the Clydonitaceae, Mojsisovics 1879, of the Treatise, Part L; Kummel perhaps because the Trachyceratidae is one of two ancestral families while the Clydonitidae comprise a derived group. Tozer separated Trachycerataceae from Clydonitoidea, rearranging both, leaving Clydonitoidea with the original Clydonitidae, Clionititidae, and Metasibiritidae to which are added the Sandlingitidae and Thetiditidae. The emended Trachycerataceae includes the Trachyceratidae, Arpaditidae, Cyrtopleuritidae, Distichitidae, Heraclitidae, Noridiscitidae, and Tibetitidae.

Phylogeny

According to Kummel (1952) and Arkel et al. (1962) in 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 ...

'', the Arpaditidae and Trachyceratidae are both derived from the Ceratitaceae. The Trachyceratidae gave rise to the Leconitidae and Tibetitdae in the upper Middle Triassic and to the Clydonitidae and Cyrtopleuritidae in the lower Upper Triassic, the Cyrtopleuritidae in turn giving rise to the mid Upper Triassic Heraclitidae. The origin of the Noridiscitidae is uncertain and may not belong. The Arpatitidae gave rise in the lower Upper Triassic to the Buchitidae, Choristoceratidae, Clionitidae, Distichitidae, and Thisbitidae. The Choristoceratidae gave rise in the mid Upper Triassic to the Cochloceratidae. Tozer distinguished the Choristoceratidae and Cochloceratidae as forming their own superfamily, the Choristocerataceae, with the addition of the Cycloceltitidae and Rhabdoceratidae.

''References''

* Arkell et al.,1962. Mesozoic Ammonoidea. Treatise on Invertebrate Paleontology, Part L, Ammonoidea. R.C. Moore (ed) * Kümmel, B. 1952. A Classification of the Triassic Ammonoids. Journal of Paleontology, V.26, N.5, pp847–853, Sept. 1952. : Tozer i
Paleobiology Database
Ceratitida superfamilies Middle Triassic first appearances Late Triassic extinctions {{Ceratitida-stub