Gymnitidae

Gymnitidae is a family of Lower to Middle Triassic ammonite cephalopods with evolute, discoidal shells.

Gymnitidae Temporal range:
Gymnites incultus from Bosnia, on display at Galerie de paléontologie et d'anatomie comparée in Paris
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	†Ammonoidea
Order:	†Ceratitida
Superfamily:	†Pinacoceratoidea
Family:	†Gymnitidae Waagen, 1898
Genera
See text

Hyatt and Smith (1905, p. 114-115) included the Gymnitidae in the suborder Ceratitoidea, which later became the superfamily Ceratitaceae and included in it genera more primitive than Gymnites as well as the more advanced Gymnites. Those being Xenaspis, Flemingites, and Ophiceras. Derivation as shown in Smith (1932 p. 30) is from Xenodiscus.

The more primitive Xenaspis, Flemingites, and Ophiceras, found in Lower Triassic beds in western America have ceratitic sutures. The more developed Gymnites has deeply digitate ammonitic sutures.

Arkell, et al., 1957, in the Treatise on Invertebrate Paleontology, on the other hand included the Gymnitidae in the Pinacocerataceae as the earlier and more primitive of its two families, combining Gymnites with coeval and more advanced forms. Genera included in the Gymnitidae sensu Arkell include Eogymnites, Buddhaites, Japanites, and of course, Gemnites. The genus Xiphogymnites was included by Tozer in 1981.

Whether to place the Gymnitidae in the Ceratitaceae, as in Hyatt and Smith, combining Gymnites with its more primitive relatives, or in the Pinacocerataceae, as in Arkell et al., combining Gymnites with its coeval or more advanced relatives is a matter of perspective which does little to change the overall phylogeny.

References

• Arkell, et al., 1957. Mesozoic Ammonidea. Treatise on Invertebrate Paleontology, Part L, Ammonoidea. Geol Soc of America and Univ. Kansas Press.
• Alpheus Hyatt and James Perrin Smith, 1905. The Triassic Cephalopod Genera of America. U.S. Geological Survey Professional Paper no. 40. (p. 114-115)
• James Perrin Smith, 1932. Lower Triassic Ammonoids of North America. U.S. Geological Survey Professional Paper no. 167 (p. 30)