Lambeoceras

Taxobox
fossil_range = M-U Ordovician
name = " Lambeocears "


regnum = Animalia
phylum = Mollusca
classis = Cephalopoda
subclassis = Nautiloidea
ordo = Actinocerida
familia = Lambeoceratidae
genus = " Lambeoceras "
genus_authority = Foeste, 1917

"Lambeoceras" is a unique actinocerid characteristic of Red Riveran faunas in North America. "Lambeoceras" is of medium to moderately large with a long straight depressed shell, broad in cross section with the dorsum and venter both about equally convex, meeting acutely along the sides. Chambers are short, septa close spaced, forming broad lobes on the upper and lower sides which meet in sharp saddles along the sides. The siphuncle is submarginal, near the ventral side and relatively narrow. Septal necks are extremely long, brims short and recumbent. Segments are broadly expanded, connecting rings thin. Radial canals within the siphuncle from broad arcs that may bifurcate close to the parispatium.

The "Treatise" (Teichert 1964) includes "Lambeoceras" with "Gonioceras" in the Gonioceratidae, both being depressed in section. Flower ( 1968, 1976 ) recognizing important distinctions having to do with the sutures and the siphuncle placed "Lambeoceras "in its own family, the Lambeocertidae.

"Lambeoceras" is likely derived from "Actinoceras" near the end of the Middle Ordovician, although consideration has been given to "Armenoceras" at about the same time.

"Lambeoceras" is found with "Actinoceras", "Armenoceras", and "Nybyoceras" in the Second Value Formation in New Mexico; with "Armenoceras" and "Selkirkoceras" in the Burnam Limestone in central Texas; with "Actinoceras", "Paractinoceras", and "Kochoceras" in the Lander Sandstone in Wyoming, and with "Armenoceras". "Actinoceras", and "Selkirkoceras" in the overlying dolomite – all of Red River age, marking the transition between the Middle and Upper Ordovician. "Lambeoceras" is also found with "Actinoceras" in the Dog Head member of the Red River Series in Manitoba and with "Actinoceras" and "Kochoceras" in the Mt. Silliman beds on Baffin Island.

Speculatively, "Lambeoceras" may have had a similar life style to that of the earlier "Gonioceras", only "Lambeoceras" may have hunted more actively over the sea floor, rather than waiting in ambush on the sea floor.

References

*Flower, R.H, 1957, Studies of the Actinoceratida, New Mexico Bureau of Mines and Mineral Resources, Memoir 2.
*Flower, R.H. 1968, The First Great Expansion of the Actinoceroids; New Mexico Bureau of Mines and Mineral Resources, Memoir 2, Pt i.
*Flower, R.H, 1978, Ordovician Cephalopod Faunas and Their Role in Correlation; in The Ordovician System: proceedings of a Palaeontological Association symposium; Bassett, M.G. (Ed)
*Teichert, C, 1964, Actinoceratoidea, in the Treatise on Invertebrate Paleontology, pub Univ of Kansas and the GSA, Vol K, p K208-210