Trigonocerataceae

Trigonocerataceae Temporal range: U Devonian - U Triassic
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Order:	Nautilida
Superfamily:	Trigonocerataceae Kummel (1964)
Families
Trigonoceratidae Centroceratidae Grypoceratidae Permoceratidae Syringonautilidae

The Trigonocerataceae is a superfamily within the Nautilida that ranged from the Devonian to the Triassic that is thought to have contained the source for the Nautilaceae in which Nautilus is found.

Trigonocerataceae are characterized by open-spiraled, gyroconic, to closed, nautiliconic shells in which the whorl section is quadrate in primitive forms; the venter typically narrow to acute, the dorsum broad. In some advanced forms the venter may become concave or broad and rounded and In some the surfaces may be strongly lirate.

Classification and phylogeny

The Trigonocerataceae is based on the Family Trigonoceratidae of Hyatt, 1884, with which other phylogenetically related families are combined, and is equivalent to the abandoned Centroceratida of Flower in Flower and Kummel 1950, and to the Centroceratina of Shimanskiy 1957, revised to the Centrocerataceae, Shimanskiy 1962.

The Trigonocerataceae combines five families, the type, Trigonoceratidae, along with the Centroceratidae, Grypoceratidae, Permoceratidae, and Syringonautilidae. Phylogenetic study and age shows that the Centroceratidae are the root stock in spite of having been first recognized 16 years after the Trigonoceratidae were first described.

The Centroceratidae gave rise to the Trigonoceratidae and Grypoceratidae in the Early MIssissippian while continuing until the very early Permian. The Trigonoceratidae which ranged into the Permian left to descendants. The Grypoceratidae which ranged almost to the end of the Triassic gave rise to two small families, the Permian Permoceratidae and the Triassic Syringonautilidae. The Syringonautilidae, in turn, is the source for the Nautilidae (Nautilaceae) which contains the genus Nautilus.

Families

The Trigononoceratidae, type family, named by Hyatt, 1884, which are loosely coiled to evolute, with oval to subquadrate, compressed to depressed whorl sections, and generally with longitudinal riidges or lirae. Sutures are typically slightly sinuous; the siphuncle small, subcentral, and orthochoanitic. In all the umbilicus is open and perforate. Includes some 17 genera.

The Centroceratidae, ancestral stock, proposed by Hyatt in 1900, consists of gyroconic to evolute and involute shells that have a quadrngular cross section in which the venter is much narrower that the dorsum, the venereal and umbilical shoulders usually angular, the flanks flattened and converging on the venter. Sutures form lobes on the sides and venter but are transverse across the dorsum. The siphuncle is tubular, orthochoanitic, and close to but not on the ventral margin. Includes some six genera.

The Grypoceratidae, predominant stock, established by Hyatt in 1900, is characterized by generllly smooth, compressed, evolute to involute shells with the venter flattened to subangular Ornamenation is not common but some forms bear nodes or keels. Sutures have distinct ventral and lateral lobes. The siphuncle, which is narrow and tubular, is variable in position. Includes about 13 genera.

Shimanskiy separated the Domatoceratidae, typified by the Permian Domatoceras, from the Grypoceratidae in the Treatise (Kummel, 1964), leaving the Grypoceratidae for mostly earlier forms.

The Permoceratidae, a Permian offshoot named by Miller and Collinson in 1953 for the genus Permoceras, is involute, smooth, with a compressed, higher than wide, whorl section, ventrally subcentral siphuncle, and a suture with a deep, narrow, pointed ventral lobe and large pointed lateral lobes, mimicking contemporary goniatites.

The Syringonautilidae, a Triassic offshoot named by Mojsisovics,1902, which gave rise to the Nautilaceae (Nautilina);containing five genera which have generally smooth, involute shells with slightly sinuous sutures and a variably positioned siphuncle.

References

• Flower, R.H and Kummel, B. 1950; A Classification of the Naulioidea; Journal of Paleontology, V 24, no 5. pp604–616, Sept 1950
• Flower, R.H. 1988; Progress and Changing Concepts in Cephalopod and Particularly Nautiloid Phylogeny and Distributuion, in Cephalopods, Present and Past, pp 17–24, Wiedmann, J, & Kullmann, J (Eds).
• Kummel, B, 1964; __ Nautilida; Treatise on Invertebrate Paleontology Part K Nautiloidea; Geological Society of America and University of Kansas Press.
• Teichert, C & Moore, R.C 1964; Classification and Stratigraphic Discribution ( Endoceratoidea - Actinoceratoidea -Nautiloidea) ibid.