| Cyrtobaltoceras Temporal range: | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Order: | † Orthocerida |
| Family: | † Baltoceratidae |
| Genus: | † Cyrtobaltoceras Flower (1964) |
Cyrtobaltoceras is an extinct cephalopod genus known from the upper Lower Ordovician Fort Cassin Formation at Valcour, N.Y. that is included in the Nautiloid family Baltoceratidae
Cyrtobaltoceras was named by Flower (1964 [1] who then assigned it to the Baltoceratidae which at that time was included in the Ellesmerocerida. The Baltoceratidae, along with included genera, has since been moved to the Orthocerida. [2]
The genotype, Cyrobaltoceras gracile Flower, is based on a small, slender, incomplete, 25 mm long shell with a slight exogastric curvature. Sutures form lobes across the ventral side but go transversely straight across the dorsum. The siphuncle is proportionally large, almost half the shell diameter in width, and lies against the ventral margin.
The holotype of Cyrtobaltoceras gracile, Reusseau Flower's no. 341, is housed in the paleontological collection of the New Mexico Museum of Natural History and Science in Albuquerque, N.M (U.S.A)
Plectronocerida is a primitive order from which subsequent cephalopod orders are ultimately derived.
The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician.
Baltoceras is a member of the Ellesmerocerida, included in the family, Baltoceratidae. The shell of Baltoceras is slender with a subcircular cross section, straight transverse sutures, and a large siphuncle in contact with the venter. Septal necks are short but not vestigial; connecting rings are thick; endosiphonal organic deposits are unknown.
Clarkoceras is a genus of breviconic ellesmerocerid cephalopods, one of only two genera known to have crossed from the Late Cambrian, Trempealeauan, into the Early Ordovician, Gasconadian. ; the other being Ectenolites.
The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician. They are characterized by straight and endogastric shells, often laterally compressed, so the dorso-ventral dimension is slightly greater than the lateral, with close spaced sutures having shallow lateral lobes and a generally large tubular ventro-marginal siphuncle with concave segments and irregularly spaced diaphragms. Connecting rings are thick and layered, externally straight but thickening inwardly with the maximum near the middle of the segment so as to leave concave depressions on internal siphuncle molds. Septal necks are typically orthochoanitic but vary in length from almost absent (achoanitic) to reaching halfway to the previous septum (hemichoanitic) and may even slope inwardly (loxochoanitic).
Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, existing for approximately 20 million years.
Cyptendoceras is an extinct nautiloid cephalopod included in the family Ellesmeroceratidae that lived in what would be North and South America during the latter part of the Early Ordovician from about 475 – 472 mya, existing for approximately 3 million years.
Endorioceras is an extinct genus of actively mobile carnivorous cephalopod of the family Baltoceratidae that lived in what would be North America during the Ordovician from 490–479 mya, existing for approximately 11 million years.
Rioceras is an extinct genus of orthocerid cephalopods of the family Baltoceratidae that lived in what would be North America during the Early Ordovician from 480—472 mya, existing for approximately 8 million years.
Microbaltoceras is an extinct genus of the cephalopod family Baltoceratidae that lived in what would be North America during the Early Ordovician. It was named by Rousseau Flower (1964) and assigned by him to the Baltoceratidae. The type species is Microbaltoceras minore which was found in the Threadgill Member of the Tanyard Formation in Gillespie County, Texas, USA.
Metabaltoceras, first described by Rousseau Flower in 1964, is a fossil cephalopod genus in the family Baltoceratidae, with a small, slender, fairly fusiform shell, and a large empty siphuncle in contact with the ventral surface. The siphuncle is achoanitic, having virtually no septal necks, segments formed all but entirely by connecting rings. Shells are generally straight, beginning with a subcircular cross section in the adapical portion but becoming faintly depressed adorally. Sutures are straight and transverse except ventrally, where they produce deep, prominent lobes.
Basslerocerida is an order of nautiloid cephalopods from the Ordovician comprising exogastric longiconic cyrtocones, that is no longer in common use.
Protcycloceratidae is an extinct family of slender, commonly annulate, members of the cephalopod order Ellesmerocerida that lived during the Early Ordovician.
Paradakeoceras is a genus of early Ordovician cephalopods belonging to the nautiloid order Ellesmerocerida.
Conostichoceras is a genus of exogastric, breviconic oncocerids included in the family Nothoceratidae, known from the Middle Devonian of central Europe and Upper Devonian of Australia. It probably lived on and swum above the sea floor.
Dakeoceras is a genus of simple cyrtoconic ellesmeroceratid cephalopods in the fossil record. All known species come from the Lower Canadian epoch (Gasconadian) of North America.
Plectronoceratoidea is a superorder or subclass containing primitive nautiloids from the Late Cambrian and Early Ordovician. This group is best considered a paraphyletic grade of early cephalopods, as it contains the ancestors of subsequent post-Cambrian cephalopod orders.
Cartersoceras is a genus of nautiloid cephalopods placed in the Orthocerid family Baltoceratidae, established by Rousseau Flower (1964), for species formally included in part in Murrayoceras, and in part in "Sacotoceras". This group is typical of Murrayoceras in all features except that the siphuncle segments are convex in outline. It is known from the Middle Ordovician of the eastern United States.
Murrayoceras is a nautilid cephalopod included in the orthocerid family Baltoceratidae, widespread in the Middle Ordovician of North America, characterized by a depressed orthoconic shell with a subtriangular cross section and flattened venter and a proportionally large ventral siphuncle, 0.15 to 0.3 the dorso-ventral shell diameter. Septa are close spaced with sutures forming broad lobes on the upper flanks and ventral surface.
Ellesmeroceras is the type genus for the Ellesmeroceratidae, a family of primitive nautiloid cephalopods, that is characterized by its small, generally compressed, gradually expanded, orthoconic shell, found in Lower Ordovician marine sediments. The septa are close spaced and the siphuncle is ventral, about 0.2 the diameter of the shell. Septal necks are typically orthochoanitic but may slant inwardly (loxochoanitic) or reach halfway to the previous septum (hemichoanitic). Connecting rings are thick. As common for the Ellesmerocerida, Ellesmeroceras has diaphragms within the siphuncle tube.
