Gymnitidae
Encyclopedia
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.
Hyatt and Smith (1905, p.114-115) included the Gymnitidae in the suborder Ceratitoidea, which later became the superfamily Ceratitaceae
Ceratitaceae
The Ceratitaceae is a superfamily in the ammonoid cephalopod order Ceratitida characterised in general by highly ornamented or tuberculate shells with ceratitic sutures that may become goniatitic or ammonitic s some offshoots....
and included in it genera more primitive than Gymnites
Gymnites
Gymnites is a genus of ammonoid cephalopod from the Middle Triassic belonging to the ceratitid family Gymnitidae.-Description:The shell of Gymnites is evolute, generally smooth, with a wide umbilicus. Whorls are moderately embracing, whorl section oval and somewhat compressed. The outer whorl may...
as well as the more advanced Gymnites. Those being Xenaspis, Flemingites, and Ophiceras. Derivation as shown in Smith (1932 p.30) is from Xenodiscus
Xenodiscus
Xenodiscus is an extinct ammonoid cephalopod genus and one of the earliest ceratites, found in the Upper Permian of northern India and Timor. Xenodiscus is included in the family Xenodiscidae which is part of the ceratite superfamily Xenodiscaceae...
.
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
Pinacocerataceae
The Pinacocerataceae are generally smooth, compressed, evolute to involute ammonoids from the Triassic, belonging to the Ceratitida, in which the suture is ammonitic, with adventitious and auxiliary elements....
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
Gymnites
Gymnites is a genus of ammonoid cephalopod from the Middle Triassic belonging to the ceratitid family Gymnitidae.-Description:The shell of Gymnites is evolute, generally smooth, with a wide umbilicus. Whorls are moderately embracing, whorl section oval and somewhat compressed. The outer whorl may...
, 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)