Gymnitidae
| Gymnitidae Temporal range: L-M Triassic
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| Family: | †Gymnitidae Waagen, 1898
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The Gymnitidae is a family of Lower to Middle Triassic ammonoid cephalopods (ammonites s.l.) with evolute, discoidal shells.
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.
Whether to place the Gymnitidae in the Ceratitaceae, as in Hyatt and Smith, combing Gymnites with its more primitive relatives, or in the Pinacocerataceae, as in Arkell et al, combing 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)
