Dakeoceras
Encyclopedia
Dakeoceras is a simple cyrtoconic ellesmeroceratid
genus, all known species of which come from the Lower Canadian
(Gasconadian
) of North America.
The Dakeoceras shell is an endogastric cyrtocone with the siphuncle
on the concave, ventral, side; moderately curved and expanded in the juvenile stages which become reduced in the adult.
Forms in which the cross section is broadened, with the venter becoming flattened, are separated as Paradakeoceras
. Quebecoceras
is also similar but for its circular cross section and more persistent rate of expansion and curvature. Levisoceras
is more compressed, more strongly curved, and has a higher rate of expansion especially in the vertical plane.
Ellesmeroceratidae
The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician...
genus, all known species of which come from the Lower Canadian
Canadian Epoch
The Canadian is the Lower or Early Ordovician in North America. The term is common in the older literature and has been well understood for more than a century...
(Gasconadian
Gasconadian Stage
The Gasconadian Stage is the first stage of the Ordovician geologic period in North America and of the Lower Ordovician Canadian Epoch, coming immediately after the Late Cambrian Trempealeauan and preceding the middle Canadian Demingian Stage...
) of North America.
The Dakeoceras shell is an endogastric cyrtocone with 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...
on the concave, ventral, side; moderately curved and expanded in the juvenile stages which become reduced in the adult.
Forms in which the cross section is broadened, with the venter becoming flattened, are separated as Paradakeoceras
Paradakeoceras
Paradakeoceras is an early Ordovician cephalopod belonging to the nautiloid order Ellesmerocerida.- Morphology :The shell of Paradakeoceras is an expanding endogastric cyrtocone with the siphuncle situated near the shell's concave margin....
. Quebecoceras
Quebecoceras
Quebecoceras is an extinct genus from the nautiloid order Ellesmerocerida that lived during the Gasconadian Stage at the beginning of the Early Ordovician....
is also similar but for its circular cross section and more persistent rate of expansion and curvature. Levisoceras
Levisoceras
Levisoceras is an early Ordovician ellesmerocerid cephalopod.- Morphology :Levisoceras is a distinctive ellesmeroceratid that combines rapid expansion a strong endogastric curvature. The cross section is compressed with the height increasing more rapidly than the width. The siphuncle is ventral and...
is more compressed, more strongly curved, and has a higher rate of expansion especially in the vertical plane.
references
- Flower, R.H. 1964. The Nautiloid Order Ellesmerocerida (Cephalopoda); Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro N.M.
- W. M. Furnish & Brian F. Glenister, 1964. Nautiloidia --Ellesmerocerida. Treatise on Invertebrate Paleontology, Part K. Geological Society of America, Teichert and Moore (eds).