| Campbelloceras Temporal range: Lower Ordovician | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Subclass: | Nautiloidea |
| Order: | Tarphycerida |
| Family: | Tarphyceratidae |
| Genus: | Campbelloceras Ulrich and Foerste, 1936 |
Campbelloceras is a tarphyceratid nautiloid known from the Lower Ordovician, Upper Canadian Epoch of North America, where it is widespread. Campbelloceras was named by Ulrich and Foerste in 1936.
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 Estonioceratidae.
Nautiloids are a large and diverse group of marine cephalopods (Mollusca) belonging to the subclass Nautiloidea that began in the Late Cambrian and are represented today by the living Nautilus and Allonautilus. Nautiloids flourished during the early Paleozoic era, where they constituted the main predatory animals, and developed an extraordinary diversity of shell shapes and forms. Some 2,500 species of fossil nautiloids are known, but only a handful of species survive to the present day.
The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period 485.4 million years ago (Mya) to the start of the Silurian Period 443.8 Mya.
The shell of Campbelloceras has a circular whorl section, only slightly impressed, and a siphuncle that is close to the venter in all growth stages. Campbelloceras differs from Tarphyceras in that the rate of expansion is greater, the siphuncle is proportionally largers, and an impression is shallower.
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 the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the walls dividing the chambers.
Tarphyeras is a genus of tarphyceratid with whorls rounded in cross section, having a deeply impressed dorsum and a ventral to subcentral siphuncle, known from the Lower Ord of North America. It differs from Campbelloceras in that Campbelloceras is only slightly impressed, from Centrotarphyceras in that Centrotarphyceras is subquadrate and has a central siphuncle, and from Trocholites in that although Trocholites is subcircular in cross section, the siphuncle is subdorsal.
Campbelloceras may have given rise to the barrandeocerid Plectoceras (Plectoceratidae) through simplification of the connecting rings, and to Tarphyceras through tighter coiling, development of a deeper impression, and reduction in the size of the siphuncle. Campbelloceras may be conceivably derived from Estonioceras (Estonioceratidae). The cross section of Campbelloceras and that of the outer whorl of Estonioceras are similar, except for Campbelloceras being slightly impressed. Both have proportionally large siphuncles, near the venter.
Plectoceras is a genus of nautiloids included in the tarphycerid suborder Barrandeocerina that lived during the Middle and Late Ordovician. It has been found widespread in the Middle and Upper Ordovician of North America.
The Plectoceratidae is a family of tarphycerids in the suborder Barrandeocerina established as a place for the genus Plectoceras; defined simply as coiled, costate barrandeocerids with subcentral adult siphuncle.
Estonioceras is an extinct genus of tarphyceridan nautiloids from the Ordovician of Europe.
