Cyrtonybyoceras
Encyclopedia
Cyrtonybyoceras is a slightly exogastric member of the Wutinoceratidae
, a family of actinocerids
and probably derived from an earlier Wutinoceras
. The shell of Cyrtonybyoceras is curved slightly upwardly and is slightly compressed. Sutures slope toward the aperture, from the dorsum to the venter. The siphuncle is ventral but not marginal, in general form like that of Nybyoceras
. Upper and lower septal necks are recumbent or narrowly free. The canal system is reticular, characteristic of the Wutinoceratidae.
Cyrtonybyoceras and Wutinoceras are similar, except for Cyrtonybyoceras being slightly cyrtoconic, and almost intergrade.
Cyrtonybyoceras is so far known only from the Whiterock Stage
in North America. The genotype, Cyrtonybyoceras haesitans was named by Teichert in 1933, based on Orthoceras haesitans Billings 1865, from the Tablehead formation in Newfoundland. Cyrtonybyoceras has also been found in the Antelope Valley
Limestone in the Toquima Range
in Nevada.
Wutinoceratidae
The Wutinoceratidae is a family of early actinocerids defined by Shimazu and Obata in 1938 for actinocerids with thick connecting rings and a complex irregular canal system...
, a family of actinocerids
Actinocerida
The Actinocerida comprise an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposits formed within contain a system of radial...
and probably derived from an earlier Wutinoceras
Wutinoceras
Wutinoceras, orthoconic actinocerids with ventral siphuncles composed of broadly expanded segments.and the type genus of the Wutinoceratidae. -Distinguishing Characters:...
. The shell of Cyrtonybyoceras is curved slightly upwardly and is slightly compressed. Sutures slope toward the aperture, from the dorsum to the venter. The siphuncle is ventral but not marginal, in general form like that of Nybyoceras
Nybyoceras
Nybyoceras is an actinocerid genus assigned to the Armenoceratidae and similar to Armenoceras except for having a siphuncle close to the ventral side of the shell.-Morphology:...
. Upper and lower septal necks are recumbent or narrowly free. The canal system is reticular, characteristic of the Wutinoceratidae.
Cyrtonybyoceras and Wutinoceras are similar, except for Cyrtonybyoceras being slightly cyrtoconic, and almost intergrade.
Cyrtonybyoceras is so far known only from the Whiterock Stage
Whiterock Stage
The Whiterockian, often referred to simply as the Whiterock, is a earliest or lowermost stage of the Middle Ordovician.. Although the Whiterockian or Whiterock Stage refers mainly to the early Middle Ordovician in North America, it is often used in the older literature in a global sense.The...
in North America. The genotype, Cyrtonybyoceras haesitans was named by Teichert in 1933, based on Orthoceras haesitans Billings 1865, from the Tablehead formation in Newfoundland. Cyrtonybyoceras has also been found in the Antelope Valley
Antelope Valley (Eureka County)
The Antelope Valley of southern Eureka County is a small 35 mi long valley, surrounded by four mountain ranges. Antelope Wash flows north, to endorheic flatlands at the valley's north end. Eureka, Nevada lies 20 mi east nestled among mountain ranges. From Eureka U.S...
Limestone in the Toquima Range
Toquima Range
The Toquima Range is a line of mountains in northwestern Nye County, in central Nevada in the western United States. From Hickson Summit on U.S. Route 50, the range runs for approximately 71 miles to the south-southwest. To its west are Big Smoky Valley, scenic State Route 376, and the large...
in Nevada.