Curtoceras
Encyclopedia
Curtoceras is a genus in the tarphycerid
family Trocholitidae
found widespread in the late Early and Middle Ordovician of North America and northern Europe. Curtoceras has a shell that is gradually expanded, with half the fully mature body chamber divergent from the preceding volution. Whorl sections are near equidimentional with the inner margin (dosum) moderately impressed. The surface may be smooth or weakly ribbed. The siphuncle
is ventral in the initial chamber and becomes dorsal after one volution. With the exception of the dorsal siphuncle, Curtoceras is somewhat similar to the tarphyceratid
Campbelloceras
Tarphycerida
The Tarphycerida were the first of the coiled cephalopods. They are found in marine sediments from the Lower Ordovician to the Middle Devonian. Some like Aphetoceras and Estonioceras are loosely coiled, gyroconic, others like Campbelloceras, Tarphyceras, and Trocholites are tightly coiled, but...
family Trocholitidae
Trocholitidae
The Trocholitidae are Tarphycerida with whorls in close contact as with the Tarphyceratidae, but in which the siphuncle, similar in structure, becomes dorsal. The Trocholitidae are derived from the Tarphyceratidae, perhaps from different tarphyceratids....
found widespread in the late Early and Middle Ordovician of North America and northern Europe. Curtoceras has a shell that is gradually expanded, with half the fully mature body chamber divergent from the preceding volution. Whorl sections are near equidimentional with the inner margin (dosum) moderately impressed. The surface may be smooth or weakly ribbed. 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...
is ventral in the initial chamber and becomes dorsal after one volution. With the exception of the dorsal siphuncle, Curtoceras is somewhat similar to the tarphyceratid
Tarphyceratidae
The Tarphyceratidae are tightly coiled, evolute Tarphycerida with ventral siphuncles. The dorsum is characteristically impressed where the whorl presses against the venter of the previous. The Tarphyceratidae are derived from Bassleroceras or possibly from some member of the...
Campbelloceras
Campbelloceras
Campbelloceras: a tarphyceratid with a circular whorl section, only slightly impressed, and a siphuncle that is close to the venter in all growth stages. Differs from Tarphyceras in that the rate of expansion is greater, the siphuncle is proportionally largers, and an impression is shallower...