The Barrandeocerina comprise a suborder of Early

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

nautiloid Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s, primitively coiled but later forms may be cyrtoconic, gyroconic, torticonic, and even breviconic, all having empty

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

s with thin connecting rings. The Barrandeocerina were originally defined as a separate order by

Rousseau Flower Rousseau Hayner Flower (1913–1988) was an extremely prolific 20th century paleontologist, known for his eccentric personality. Career Although trained as an entomologist, and a specialist in dragonflies and orthopterans, Flower began study ...

(Flower and Kummel, 1950), but since then have been united within the

Tarphycerida The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician (middle and upper Canad) to the Middle Devonian. Some, such as '' Aphetoceras'' and '' Estonioceras'', are loosely coiled and gyroconi ...

as a suborder (Teichert 1988). Derivation is from the

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'' o ...

. In early forms the siphuncle is central or subcentral, orthochoanitic (septal necks short and straight), and thin, with tubular segments. Later forms include those with cyrtochoanitic septal necks (curved outward) and segments that may be slightly to strongly expanded into the chambers.

Taxonomy

Six families are included in the Barrandeocerina, (ex Barrandeocerida). :

Barrandeoceratidae The Barrandeoceratidae is a family of coiled nautiloids included in the Tarphycerida (''sensu lato'') that lived from the Middle Ordovician to the Middle Devonian, characterised by mostly compressed shells with a subcentral siphuncle composed of ...

M Ord-M Dev : Plectoceratidae M-U Ord : Apsidoceratidae M-U Ord :

Uranoceratidae The Uranoceratidae is a family of Silurian barrandeoceroids that tend to become uncoiled with age and in which siphuncle segments tend to be expanded into the camerae.Flower, R.H. & Kummel, B. 1950. A Classification of the Nautiloidea. Journal ...

U Ord-M Sil :

Lechritrochoceratidae Lechritrochoceratidae is a family of derived Tarphycerida, tarphycerids from the middle and upper Silurian, once included in the now largely abandoned Barrandeocerida. Description Lechritrochoceratidae comprise dextrally torticonic genera with c ...

M-U Sil : Nephriticeratidae L-M Dev Flower also included the

Lituitidae The Lituitidae are a family of evolved tarphycerids characterized by a long orthoconic section that follows a coiled juvenile portion at the apex, along with a generally tubular siphuncle, which like that of the barrandeocerids is composed of t ...

in the Barrandeocerida, (Flower and Kummel 1950), which were found (Sweet 1964) to have more in common with the Tarphycerida in the original Treatise Part K.

References

*Rousseau H Flower and Bernhard Kummel Jr 1950. A Classification of the Nautiloidea. Journal of Paleontology Vol 24, no.5 pp604–616, Sept 1950 *Walter C Sweet, 1964, Nautiloidea - Barrandeocerida.

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

Part K Mollusca 3. Geological Society of America and University of Kansas Press *Curt Teichert, 1988. Main Feature of Cephalopod Evolution. The Mollusca Vol.12 Paleontology and Neontology of Cephalopods. Academic Press Prehistoric nautiloids Mollusc suborders Prehistoric animal suborders Taxa named by Rousseau H. Flower {{paleo-nautiloid-stub