Meniscoceras
Encyclopedia
Meniscoceras is a straight and slender Chazyan endocerid described by Rousseau Flower in 1941 The genus was originally included in the Proterocameroceratidae
(Flower 1955) but later (Flower 1976) placed with its predecessor, Najaceras
, in the Najaceratidae.
The siphuncle
in Mensicoceras is large with short septal necks and thin connecting rings. Endocones are vertically asymmetric. The central cavity is dorsally concave where a broad dorsal process is formed in which is said to contain a pair of dorso-lateral blades, and flat ventrally.
Mensicoceras from the Chazy and the earlier Najaceras from the Whiterock age are similar in having a longitudual process formed along the inner dorsal side of the siphuncle
around which the endocones form, but differ in details such as with the central opening. On that basis the two have been separated into their own family, the Najaceratidae (Flower 1971,1976). The Treatise on Invertebrate Paleontology
(1964) shows Meniscoceras in the Proterocameroceratidae, a carry over from before the time its ancestor, Najaceras was discovered.
The genotype, Meniscoceras coronense, is known from the Chazyan of New York State.
Proterocameroceratidae
The Proterocameroceratidae were the first of the Endocerida. They began early in the Ordovician with Proendoceras or similar genus which had developed endocones, replacing the diaphragms of the ellesmerocerid ancestor....
(Flower 1955) but later (Flower 1976) placed with its predecessor, Najaceras
Najaceras
Najaceras is a genus of straight, slender endocerid known only from the Whiterockian age Oil Creek Limestone of Oklahoma, introduced and named by Rousseau Flower in 1971 and further described by him in 1976....
, in the Najaceratidae.
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...
in Mensicoceras is large with short septal necks and thin connecting rings. Endocones are vertically asymmetric. The central cavity is dorsally concave where a broad dorsal process is formed in which is said to contain a pair of dorso-lateral blades, and flat ventrally.
Mensicoceras from the Chazy and the earlier Najaceras from the Whiterock age are similar in having a longitudual process formed along the inner dorsal side of 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...
around which the endocones form, but differ in details such as with the central opening. On that basis the two have been separated into their own family, the Najaceratidae (Flower 1971,1976). The Treatise on Invertebrate Paleontology
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...
(1964) shows Meniscoceras in the Proterocameroceratidae, a carry over from before the time its ancestor, Najaceras was discovered.
The genotype, Meniscoceras coronense, is known from the Chazyan of New York State.