Centroceratidae
Encyclopedia
The Centroceratidae is the ancestral family of the Trigonocerataceae
and of the equivalent Centroceratina; extinct shelled cephalopods belonging to the order Nautilida
to the Lower Permian
, are characterized by gyroconic, evolute tarphyceraconic, and involute nautiliconic shells with compressed whorls, typically with a quadrangular whorl section in which the flanks converge on venter that is much narrower than the dorsum and ventral and umbilical shoulders are sharply angular, or rarely rounded. In some, e.g. Centroceras, the flanks are divided by a ridge that runs along the middle. Sutures have ventral and lateral lobes but are transverse dorsally. The siphuncle
is tubular and close to but not on in contact with the venter (Kummel 1964).
stock (Flower 1950, 1988, Kummel 1964) Earliest are Centroceras, Homaloceras
, and Strophiceras
.from the Middle Devonian; Centroceras and Homaloceras from North America, Strophiceras from Europe. Next is Carlloceras from the Upper Devonian of North America, followed by Diorugoceras from the Lower Carboniferous of Europe. Last is Phacoceras, found in the Lower Carboniferous of Europe and Lower Permian of Australia. (Kummel 1964)
Centroceras, the type genus, is evolute with only a few, rapidly expanding whorls and wide, perforate umbilicus. The cross section may be faintly hexagonal from the effect of a median ridge on either flank, otherwise is tetragonal. Flanks converge from a broad dorsum to a narrow, barely convex venter. Ventral and umblical shoulders are sharp. The suture is with a shallow ventral lobe and broad lateral lobes with subacute saddles on the shoulders; the siphuncle is tubular, near the venter; the living chamber half a volution in length. The surface is covered with alternating striae and lirae; fine, parallel "scratches" and "wires"
Strophiceras has a probably gyroconic shell with a higher than wide, compressed, subrectangular whorl section with slightly arched dorsum and venter and flattned flanks. The venter has a median ridge aligned with diagonally elongated nodes. The suture is with ventral and dorsal lobes, the siphuncle very close to the venter.
Carlloceras has a moderately involute shell with a compressed trapezoidal whorl section, nearly flat ventral and lateral areas, and slight dorsal impression. The suture has a ventral saddle and broad lateral lobe and the siphuncle is small and near the venter.
Diorugoceras is very involute and smooth, with a compressed whorl section with broad, slightly convex flanks that converge toward a concave venter. Ventral shoulders are angular, umbilical shoulders broadly rounded. The suture is with broad, deep lateral lobes, the nature of the ventral and lateral lobes is unknown, as is the position of the siphuncle.
Phacoceras as a moderately involute, highly compressed, smooth, lenticular shell with an acute venter and widest at the umbilical shoulder; suture with ventral saddle and broad shallow lobes on flanks; siphuncle slightly ventral from center.
Genera in ascending stratigraphic order, descriptions from Kummel 1964. p K432 in the Treatise Part K
.
Trigonocerataceae
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....
and of the equivalent Centroceratina; extinct shelled cephalopods belonging to the order Nautilida
Nautilida
The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, Nautilus and Allonautilus, with six species...
Diagnosis
The Centroceratidae, which range from the Middle DevonianDevonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
to the Lower Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
, are characterized by gyroconic, evolute tarphyceraconic, and involute nautiliconic shells with compressed whorls, typically with a quadrangular whorl section in which the flanks converge on venter that is much narrower than the dorsum and ventral and umbilical shoulders are sharply angular, or rarely rounded. In some, e.g. Centroceras, the flanks are divided by a ridge that runs along the middle. Sutures have ventral and lateral lobes but are transverse dorsally. The siphuncle
Siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...
is tubular and close to but not on in contact with the venter (Kummel 1964).
Evolutionary sequence
The Centroceratidae are thought probably to be derived from the rutoceratidRutoceratidae
The Rutoceratidae are the prototypical nautilids, derived probably from either the Brevicoceratidae or Acleistoceratidae of the Oncocerida early in the Devonian...
stock (Flower 1950, 1988, Kummel 1964) Earliest are Centroceras, Homaloceras
Homaloceras
Homaloceras is an extinct nautiloid cephalopod from the Middle Devonian with a strongly curved shell, included in the nautilid family Centroceratidae....
, and Strophiceras
Strophiceras
Strophiceras is an extinct cephalopod genus from the Order Nautilida, which includes, in a separate family, Nautilus and Allonautilus....
.from the Middle Devonian; Centroceras and Homaloceras from North America, Strophiceras from Europe. Next is Carlloceras from the Upper Devonian of North America, followed by Diorugoceras from the Lower Carboniferous of Europe. Last is Phacoceras, found in the Lower Carboniferous of Europe and Lower Permian of Australia. (Kummel 1964)
Generic descriptions
Homaloceras is the most primitive, with a laterally compressed, cyrtoconic to gyronic shell with a narrow, concave venter, broadly convex flanks, and rounded dorsum, The suture is only slightly sinuous, the siphuncle tubular and near the venter.Centroceras, the type genus, is evolute with only a few, rapidly expanding whorls and wide, perforate umbilicus. The cross section may be faintly hexagonal from the effect of a median ridge on either flank, otherwise is tetragonal. Flanks converge from a broad dorsum to a narrow, barely convex venter. Ventral and umblical shoulders are sharp. The suture is with a shallow ventral lobe and broad lateral lobes with subacute saddles on the shoulders; the siphuncle is tubular, near the venter; the living chamber half a volution in length. The surface is covered with alternating striae and lirae; fine, parallel "scratches" and "wires"
Strophiceras has a probably gyroconic shell with a higher than wide, compressed, subrectangular whorl section with slightly arched dorsum and venter and flattned flanks. The venter has a median ridge aligned with diagonally elongated nodes. The suture is with ventral and dorsal lobes, the siphuncle very close to the venter.
Carlloceras has a moderately involute shell with a compressed trapezoidal whorl section, nearly flat ventral and lateral areas, and slight dorsal impression. The suture has a ventral saddle and broad lateral lobe and the siphuncle is small and near the venter.
Diorugoceras is very involute and smooth, with a compressed whorl section with broad, slightly convex flanks that converge toward a concave venter. Ventral shoulders are angular, umbilical shoulders broadly rounded. The suture is with broad, deep lateral lobes, the nature of the ventral and lateral lobes is unknown, as is the position of the siphuncle.
Phacoceras as a moderately involute, highly compressed, smooth, lenticular shell with an acute venter and widest at the umbilical shoulder; suture with ventral saddle and broad shallow lobes on flanks; siphuncle slightly ventral from center.
Genera in ascending stratigraphic order, descriptions from Kummel 1964. p K432 in the Treatise Part K
Treatise on Invertebrate Paleontology
The Treatise on Invertebrate Paleontology 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 covering every phylum, class, order, family, and genus of fossil and...
.