Tarphycerida
Encyclopedia
The Tarphycerida were the first of the coiled cephalopods. They are found in marine sediments from the Lower Ordovician
(middle and upper Canad
) to the Middle Devonian
. Some like Aphetoceras
and Estonioceras
are loosely coiled, gyroconic, others like Campbelloceras
, Tarphyceras
, and Trocholites
are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular (Furnish and Glenister 1964), as much as half the length of the containing whorl in most, greater than in the Silurian
Ophidioceratidae
.
The Tarphycerida evolved from the elongate, 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
.
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, nekto-benthic, certainly more maneuverable
, Tarphyceratidae
, Trocholitidae
, Lituitidae
, and Ophidioceratidae
; the barradeoceratid group, derived from Centrotarphyceras
(Flower 1984), consisting of the Barrandeoceratidae
, Bickmoritidae, Nephriticeratidae, and Uranoceratidae; and the plectoceratid group, derived from Campbelloceras
(ibid), consisting of the Plectoceratidae, Lechritrochoceratidae
, and Apsidoceratidae.
The tarphyceratids comprise the Tarphycerida of the Treatise on Invertebrate Paleontology
Part K (Furnish and Glenister 1964) to which Flower added the ancestral Bassleroceratidae. The Estonioceratidae, Tarphyceratidae, and Trocholitidae are primitive forms characterized by siphuncles with thick-walled connecting rings. The Lituitidae and Ophidioceratidae are derived offshoots.
The barrandeoceratid and Plectoceratid families were once combined in the Barrandeocerida (Sweet, 1964), determined by Flower (1984) to be invalid due to having multiple ancestors in the Tarphyceriatidae and therefor abandoned. The common character of these forms are the thin-walled connecting rings in their siphuncles.
Some recent classifications (e.g. Teichert 1988) divide the Tarphycerida into to suborders, the Tarphycerina and Barrandeocerina, which were previously defined as separate orders.
, through the ancestral Bassleroceratidae in the Lower Ordovician, than to the other nautiloid orders. The Oncocerida in turn gave rise to the Nautilida
which includes the recent Nautilus
and Allonautilus
. This puts the Tarphycerida in the broad group that includes the nautilids. It makes them also separate from the groups that include the Discosorida
, Actinocerida
, Endocerida, and Orthocerida
, and from the superficially similar Ammonoidea .( Teichert and Moore 1964, Wade 1988)
.
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
(middle and upper Canad
Canadian Epoch
The Canadian is the Lower or Early Ordovician in North America. The term is common in the older literature and has been well understood for more than a century...
) to the Middle Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
. Some like Aphetoceras
Aphetoceras
Aphetoceras is a genus of Tarphycerida cephalopod within the Estonioceratidae; loosely coiled without an impression along the dorsal margin; early whorls barely teaching, separating then diverging in the final mature whorl; weakly ribbed in some. The cross section of Aphetoceras is higher than...
and Estonioceras
Estonioceras
Estonioceras is an extinct genus of tarphyceridan nautiloid from the Ordovician of Europe.-Sources:* Dinosaur Encyclopedia by Jayne Parsons* Fossils by David Ward-External links:* in the Paleobiology Database...
are loosely coiled, gyroconic, others like 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...
, Tarphyceras
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 of North America...
, and Trocholites
Trocholites
Trocholites is a tarphycerid genus in the fa mily Trocholitidae from the Middle and Upper Ordovician with a gradually expanding, weakly ribbed shell; whorls in contact, dorsum slightly impressed; cross section depressed, venter and sides rounded; siphuncle close to but not at the dorsal margin.The...
are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular (Furnish and Glenister 1964), as much as half the length of the containing whorl in most, greater than in the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
Ophidioceratidae
Ophidioceratidae
The Ophidioceratidae is a family of closely coiled tarphycerids, represented solely by the Upper Silurian genus, Ophioceras, characterized by an evolute shell with narrow, subrounded, annulated whorls and a subcentral siphuncle composed of thin connecting rings that show no evidence of layering...
.
The Tarphycerida evolved from the elongate, compressed, exogastric Bassleroceratidae
Bassleroceratidae
The Bassleroceratidae is a family of gradually expanding, smooth ellesmerocerids with a slight to moderate exogastric curvature, subcircular to strongly compressed cross section, and ventral orthochaonitc siphuncle. The ventral side is typically more sharply rounded than the dorsal side and septa...
, probably Bassleroceras
Bassleroceras
Bassleroceras is an elongate upwardly curved, exogastric, genus with the venter on the under side more sharply rouned than the dorsum on the upper...
, 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
Canadian Epoch
The Canadian is the Lower or Early Ordovician in North America. The term is common in the older literature and has been well understood for more than a century...
.
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, nekto-benthic, certainly more maneuverable
Composition and taxonomy
The Tarphycerida comprise three phylogenetically related groups of families. They are: the tarphyceratid group consisting of the EstonioceratidaeEstonioceratidae
The Estonioceratidae is 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 ventrally...
, Tarphyceratidae
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...
, 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....
, Lituitidae
Lituitidae
The Lituitidae is 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 thin connecting rings.-Taxonomic Position:Flower and...
, and Ophidioceratidae
Ophidioceratidae
The Ophidioceratidae is a family of closely coiled tarphycerids, represented solely by the Upper Silurian genus, Ophioceras, characterized by an evolute shell with narrow, subrounded, annulated whorls and a subcentral siphuncle composed of thin connecting rings that show no evidence of layering...
; the barradeoceratid group, derived from Centrotarphyceras
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...
(Flower 1984), consisting of the Barrandeoceratidae
Barrandeoceratidae
The Barrandeoceratidae is a family of coiled nautiloids included in the Tarphycerida that lived from the Middle Ordovician to the Middle Devonian, characterised by mostly compressed shells with a subcentral siphuncle composed of thin-walled segments that may become secondarily ventral..The...
, Bickmoritidae, Nephriticeratidae, and Uranoceratidae; and the plectoceratid group, derived from 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...
(ibid), consisting of the Plectoceratidae, Lechritrochoceratidae
Lechritrochoceratidae
Lechritrochoceratidae is a family of derived tarphycerids from the middle and upper Silurian, once included in the now largely abandoned Barrandeocerida, which comprise dextrally torticonic genera with costate shells and ventrally displaced siphuncles. Offset coiling in low spired. Rate of...
, and Apsidoceratidae.
The tarphyceratids comprise the Tarphycerida of 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...
Part K (Furnish and Glenister 1964) to which Flower added the ancestral Bassleroceratidae. The Estonioceratidae, Tarphyceratidae, and Trocholitidae are primitive forms characterized by siphuncles with thick-walled connecting rings. The Lituitidae and Ophidioceratidae are derived offshoots.
The barrandeoceratid and Plectoceratid families were once combined in the Barrandeocerida (Sweet, 1964), determined by Flower (1984) to be invalid due to having multiple ancestors in the Tarphyceriatidae and therefor abandoned. The common character of these forms are the thin-walled connecting rings in their siphuncles.
Some recent classifications (e.g. Teichert 1988) divide the Tarphycerida into to suborders, the Tarphycerina and Barrandeocerina, which were previously defined as separate orders.
Broader relationships
Tarphycerids are more closely related to the diverse OncoceridaOncocerida
The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian ,in which the connecting rings are thin and siphuncle segments are variably expanded...
, through the ancestral Bassleroceratidae in the Lower Ordovician, than to the other nautiloid orders. The Oncocerida in turn gave rise to the Nautilida
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 Allonautilus, with six species...
which includes the recent Nautilus
Nautilus
Nautilus is the common name of marine creatures of cephalopod family Nautilidae, the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in two genera, the type of which is the genus Nautilus...
and Allonautilus
Allonautilus
The genus Allonautilus contains two species of nautiluses, which differ significantly in terms of morphology from those placed in the sister taxon Nautilus. Allonautilus is now thought to be a descendant of Nautilus and the latter paraphyletic.-External links:*...
. 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
Discosorida is a unique 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 connects the chambers in cephalopods, which unlike...
, Actinocerida
Actinocerida
The Actinocerida comprise an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposits formed within contain a system of radial...
, Endocerida, and Orthocerida
Orthocerida
Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...
, and from the superficially similar Ammonoidea .( Teichert and Moore 1964, Wade 1988)
Tarphycerid biology
The tarphycerid animal must have been rather elongate, like squid, although no close relationship is implied. Either that or it was able to retreat deep into its portable lair. As for what ever arms or tentacles they may have had, there is no indication. What may be surmised is that they 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 coleoidsColeoidea
Subclass Coleoidea, or Dibranchiata, is the grouping of cephalopods containing all the primarily soft-bodied creatures. Unlike its sister group Nautiloidea, whose members have a rigid outer shell for protection, the coleoids have at most an internal bone or shell that is used for buoyancy or support...
.