The Tarphycerida were the first of the coiled

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

, found in marine sediments from the Lower

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

(middle and upper

Canad Canad may refer to: * Sanjak of Çanad, an Ottoman-era district * Magyarcsanád, known in Serbian as Čanad, a village in Hungary * Cenad Cenad ( hu, Nagycsanád, during the Dark Ages ''Marosvár''; german: Tschanad; sr, Чанад, Čanad; la, ...

) to the Middle

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

. Some, such as ''

Aphetoceras ''Aphetoceras'' is a genus of tarphycerid cephalopod within the Estonioceratidae; loosely coiled without an impression along the dorsal margin; early whorls barely reaching, separating then diverging in the final mature whorl; weakly ribbed in s ...

'' and ''

Estonioceras ''Estonioceras'' is an extinct genus of tarphyceridan nautiloids from the Ordovician of Europe. Sources * ''Dinosaur Encyclopedia'' by Jayne Parsons * ''Fossils'' (Smithsonian Handbooks) by David Ward External links''Estonioceras''in the Pa ...

'', are loosely coiled and gyroconic; others, such as '' Campbelloceras'', ''

Tarphyceras ''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 (U Canad) of North America. It differs from ''Campbelloceras'' in t ...

'', and ''

Trocholites ''Trocholites'' is a tarphycerid genus in the family Trocholitidae from the Middle and Late Ordovician with a gradually expanding, weakly ribbed shell; whorls in contact, dorsum slightly impressed; cross section depressed, venter and sides rounde ...

'', are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular,Furnish and Glenister 1964; Nautiloidea - Tarphycerida; In the ''Treatise on Invertebrate Paleontology'' Vol K; Teichert and Moore, (eds) GSA and U of Kansas Press 1964 as much as half the length of the containing whorl in most, greater than in the

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleoz ...

Ophidioceratidae ''Ophioceras'' is a genus of closely coiled tarphycerid nautiloid cephalopods, the sole representatives of the family Ophidioceratidae, characterized by an evolute shell with narrow, subrounded, annulated whorls and a subcentral siphuncle compo ...

. The Tarphycerida evolved from the elongated, compressed, exogastric Bassleroceratidae, probably '' Bassleroceras'', around the end of the Gasconadian through forms like ''Aphetoceras''. Close coiling developed rather quickly, and both gyroconic and evolute forms are found in the early middle

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

. Tarphycerids tend to uncoil in the late mature stage of their growth, indicating they settled into a benthic lifestyle as they became older. Younger, wholly coiled forms were probably more active, nektobenthic, certainly more maneuverable.

Composition and taxonomy

The Tarphycerida comprise three phylogenetically related groups of families. They are: the tarphyceratid group consisting of the

Estonioceratidae The Estonioceratidae are a family of loosely coiled tarphycerids in which the inner side of the whorls, which forms the dorsum, is rounded or flat with no impression, and in which the siphuncle, composed of thick tubular segments, is located ve ...

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 ...

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 tarphyce ...

, and

; the barradeoceratid group, derived from ''Centrotarphyceras'', consisting of the

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 ...

, Bickmoritidae, Nephriticeratidae, and Uranoceratidae; and the plectoceratid group, derived from '' Campbelloceras'', consisting of the

Plectoceratidae The Plectoceratidae is a family of tarphycerids in the suborder Barrandeocerina established as a place for the genus '' Plectoceras''; defined (Sweet 1964) simply as coiled, costate barrandeocerids with subcentral adult siphuncle. According to ...

, Lechritrochoceratidae, and Apsidoceratidae.Flower R.H. 1984, Bodeiceras A New Mohawkian Oxycone, with revision of the Older Barrandeocerida and Discussion of the Status of the Order; Journal of Paleontology V 58, no.6, pp1372–1379, Nov 1984 The tarphyceratids comprise the Tarphycerida of the ''

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') 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 ...

'' Part K to which Flower added the ancestral Bassleroceratidae. The Estonioceratidae, Tarphyceratidae, and Trocholitidae are primitive forms characterized by siphuncles with thick-walled connecting rings. The Ophidioceratidae are derived offshoots. The barrandeoceratid and plectoceratid families were once combined in the Barrandeocerida, determined to be invalid due to having multiple ancestors in the Tarphyceriatidae and therefore abandoned. The common characteristic of these forms is the thin-walled connecting rings in their siphuncles. A 1988 classification divides the Tarphycerida into suborders Tarphycerina and Barrandeocerina, which were previously defined as separate orders.

Broader relationships

Tarphycerids are more closely related to the diverse

Oncocerida The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian (early Carboniferous; one possible member is known from the Early Permian), in which the connecting rings are t ...

, through the ancestral Bassleroceratidae in the Lower Ordovician, than to the other nautiloid orders. The Oncocerida, in turn, gave rise to the

Nautilida The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, ''Nautilus'' and ''Allonauti ...

which include the recent ''

Nautilus The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in ...

'' and ''

Allonautilus The genus ''Allonautilus'' contains two species of nautiluses, which have a significantly different morphology from those placed in the sister taxon '' Nautilus''. ''Allonautilus'' is now thought to be a descendant of ''Nautilus'', rendering t ...

''. This puts the Tarphycerida in the broad group that includes the nautilids. It makes them also separate from the groups that include the

Discosorida Discosorida are an order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and co ...

, Actinocerida,

Endocerida Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in their siphuncle. Endocerida was a diverse group of cephalopods that lived from the Early Ordovician possibly to the Late Siluri ...

, and

Orthocerida Orthocerida is an order of extinct Orthoceratoid cephalopods also known as the Michelinocerida that lived from the Early Ordovician () possibly to the Late Triassic (). A fossil found in the Caucasus suggests they may even have survived until ...

, and from the superficially similar

Ammonoidea Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefis ...

.Wade, M, 1988; Nautiloids and their descendants: cephalopod classification in 1986; New Mexico Bureau of Mines and Mineral Resources Memoir 44, Oct 1988.

Tarphycerid biology

The tarphycerid animal must have been rather elongated, like squid, although no close relationship is implied. Either that or it was able to retreat deep into its portable lair. As for whatever arms or tentacles they may have had, no indication has been found. They probably went through two stages, first a younger more active and swimming stage with simple coiled shells, followed by a less active, bottom-dwelling stage with shells that diverge during which they mated and produced, probably a single litter of young, like the modern but unrelated coleoids.

Composition and taxonomy

Broader relationships

Tarphycerid biology

References

Further reading