Actinocerida
Encyclopedia
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 canals and a narrow space along the inner side of the connecting ring known as a paraspatium. (Teichert 1964) Septal necks are generally short and cyrtochoanitic, some being recumbent, some hook shaped. Most grew to lengths of about 60 to 90 cm ( 2-3 ft) but some, like the Huroniidae of the Silurian grew significantly larger.
The Georginidae, introduced and described by Mary Wade in 1977 (Wade 1988)., based on te genus Georgina, are known from the upper Canadian
Coolibah Formation of the Georgina Basin in Northern Australia.How the Georginidae relate to older stocks is unclear. The Upper Cambrian Protactinocerida have been suggested as being ancestral but none are known to have gone beyond the near end the Cambrian extinction, which makes any connection hypothetical.
Polydesmia was once thought to be the ancestral form of the actinocerids, and was derived from the ellesmeroceriid
Bathmoceras
. (Flower 1968). However it turned out (Flower 1976) based on a reassessment of Lower Ordovician and Whiterockian formations in northeastern China that Polydesmia
is predated by Wutinoceras
, its assumed primitive nature rather a derived condition.
in Northern Australia. They reached their greatest diversity in the Middle Ordovician with more than 20 genera, then declined somewhat in the Late Ordovician and more so in the Early Silurian; made a slight come back in the Middle Silurian but not to Late Ordovician numbers; declined more or less steadily from the Late Silurian into the Devonian
Three major lineages began the Middle Ordovician, the Actinoceratidae, Armenoceratidae, and Ormoceratidae. The Actinoceratidae and Armenoceratidae are most likely derived from Wutinoceras and the Ormoceratidae from a second wutinocerid genus, Adamsoceras
. Gonioceras
is an offshoot of an early Armenoceras; Lambeoceras
and Huronia
are offshoots of a later Actinoceras
. (Flower 1968) .
The Actinoceratidae extent into the Lower Silurian with Actinoceras
; the Armenoceratidae and Huroniidae into the Upper Silurian. The Ormoceratidae are possible the most recent, extending into the Lower Devonian Gonioceras
(Gonioceratidae) is limited to the Middle Ordovician, its quasi-lookalike Lambeoceras
(Lamberoceratidae) to the uppermost Middle and Upper Ordovician. The wutinocerids are known only from the early Middle Ordovician (Whiterockian) and the polydesmiadids are restricted to about that time.
Originating in the Ordovician, by the Devonian
period Actinocerids became rare; perhaps they were unable to compete with the more compact and maneuverable coiled nautiloid
s and ammonoids and cope with the arrival of jawed fish.
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
, distinguished by a 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...
composed of expanded segments that extend into the adjacent chambers, in which deposits formed within contain a system of radial canals and a narrow space along the inner side of the connecting ring known as a paraspatium. (Teichert 1964) Septal necks are generally short and cyrtochoanitic, some being recumbent, some hook shaped. Most grew to lengths of about 60 to 90 cm ( 2-3 ft) but some, like the Huroniidae of the Silurian grew significantly larger.
Ecology
The Actinocerida inhabited shallow to quite deep waters, where they alternated between swimming and lying on the bottom. They were predatory, and able to control their buoyancy to a greater degree than their contemporaries.Derivation
The derivation of the Actinocerida remains enigmatic.They first appear late in the Early Ordovician (Cassinian Stage, late Floian) with the Georginidae but don't become well established until the beginning of the early Whiterockian Stage (Dapingian) of the Middle Ordovician (Flower 1868,1976)The Georginidae, introduced and described by Mary Wade in 1977 (Wade 1988)., based on te genus Georgina, are known from the upper 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...
Coolibah Formation of the Georgina Basin in Northern Australia.How the Georginidae relate to older stocks is unclear. The Upper Cambrian Protactinocerida have been suggested as being ancestral but none are known to have gone beyond the near end the Cambrian extinction, which makes any connection hypothetical.
Polydesmia was once thought to be the ancestral form of the actinocerids, and was derived from the ellesmeroceriid
Ellesmerocerida
The Ellesmerocerida is a order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician.-Morphology:...
Bathmoceras
Bathmoceras
Bathmoceras is a genus of the Ellesmerocerida, placed in the family Bathmoceratidae, in which Furnish and Glenister 1964 also include Eothinceras. Flower 1964 separates the two genera into their respective families which he included in his suborder, CyrtocerininaThe shells of Bathmoceras are rather...
. (Flower 1968). However it turned out (Flower 1976) based on a reassessment of Lower Ordovician and Whiterockian formations in northeastern China that Polydesmia
Polydesmia
Polydesmia is a genus of fungi within the Hyaloscyphaceae family. The genus contains 7 species.-External links:* at Index Fungorum...
is predated by Wutinoceras
Wutinoceras
Wutinoceras, orthoconic actinocerids with ventral siphuncles composed of broadly expanded segments.and the type genus of the Wutinoceratidae. -Distinguishing Characters:...
, its assumed primitive nature rather a derived condition.
Evolution and Diversification
Actinocerids first appeared early in the Middle Ordovician, with the exception of the Georginidae which are known from the CassinianCanadian 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...
in Northern Australia. They reached their greatest diversity in the Middle Ordovician with more than 20 genera, then declined somewhat in the Late Ordovician and more so in the Early Silurian; made a slight come back in the Middle Silurian but not to Late Ordovician numbers; declined more or less steadily from the Late Silurian into the Devonian
Three major lineages began the Middle Ordovician, the Actinoceratidae, Armenoceratidae, and Ormoceratidae. The Actinoceratidae and Armenoceratidae are most likely derived from Wutinoceras and the Ormoceratidae from a second wutinocerid genus, Adamsoceras
Adamsoceras
Adamsoceras is an actinocerid of the family Wutinoceratidae, with spheroidal siphuncle segments like Ormoceras but having a reticular canal system like Wutinoceras. Adamsoceras has a slender, gently expanding, orthoconic shell that is slightly broader than high, i.e...
. Gonioceras
Gonioceras
Gonioceras is an actinocerid with a broad, low shell; flattened ventrally, convexly rounded dorsally; top and bottom meeting at an acute angle along the sides. In most the shell is rather thin, especially along the lateral portion. The aperture is contracted...
is an offshoot of an early Armenoceras; Lambeoceras
Lambeoceras
Lambeoceras is a rather large actinocerid with a convexly lenticular cross section from the Upper Ordovician of North America, and the sole representative of the family Lambeoceratidae.-Morphological Description:...
and Huronia
Huronia
Huronia is an actinocerid genus included in the Huroniidae along with Discoactinoceras and Huroniella,. Huronia is characterized by long siphuncle segments with the free part of the connecting rings only slightly inflated and by a narrow central canal and strongly curved radial canals located in...
are offshoots of a later Actinoceras
Actinoceras
Actinoceras is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician.- Morphology:...
. (Flower 1968) .
The Actinoceratidae extent into the Lower Silurian with Actinoceras
Actinoceras
Actinoceras is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician.- Morphology:...
; the Armenoceratidae and Huroniidae into the Upper Silurian. The Ormoceratidae are possible the most recent, extending into the Lower Devonian Gonioceras
Gonioceras
Gonioceras is an actinocerid with a broad, low shell; flattened ventrally, convexly rounded dorsally; top and bottom meeting at an acute angle along the sides. In most the shell is rather thin, especially along the lateral portion. The aperture is contracted...
(Gonioceratidae) is limited to the Middle Ordovician, its quasi-lookalike Lambeoceras
Lambeoceras
Lambeoceras is a rather large actinocerid with a convexly lenticular cross section from the Upper Ordovician of North America, and the sole representative of the family Lambeoceratidae.-Morphological Description:...
(Lamberoceratidae) to the uppermost Middle and Upper Ordovician. The wutinocerids are known only from the early Middle Ordovician (Whiterockian) and the polydesmiadids are restricted to about that time.
Originating in the Ordovician, by the 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...
period Actinocerids became rare; perhaps they were unable to compete with the more compact and maneuverable coiled nautiloid
Nautiloid
Nautiloids are a large and diverse group of marine cephalopods belonging to the subclass Nautiloidea that began in the Late Cambrian and are represented today by the living Nautilus. Nautiloids flourished during the early Paleozoic era, where they constituted the main predatory animals, and...
s and ammonoids and cope with the arrival of jawed fish.
Classification and Taxonomy
The Actinocerida contains nine families; the Georginidae, Wutinoceratidae, Polydesmiidae, Armenoceratidae, Ormoceratidae, Actinoceratidae, Gonioceratidae, Lambeoceratide, and Huroniidae. The Carbactinoceratidae, included in the taxonomy in the Treatise, (Vol K) have been removed to the Pseudorthocerida (Kroger and Mapes, 2007)- Georginidae, Wade 1977; late E- early M Ord., Aust, Asia; Georgina, Mesaktoceras
- WutinoceratidaeWutinoceratidaeThe Wutinoceratidae is a family of early actinocerids defined by Shimazu and Obata in 1938 for actinocerids with thick connecting rings and a complex irregular canal system...
, Shimazu and Obata, 1938, ?late E - early M Ord (Whiterock); Asia, Aust, N Am. N Eur. Wutinoceras, Cyrtonybyoceras, AdamsocerasAdamsocerasAdamsoceras is an actinocerid of the family Wutinoceratidae, with spheroidal siphuncle segments like Ormoceras but having a reticular canal system like Wutinoceras. Adamsoceras has a slender, gently expanding, orthoconic shell that is slightly broader than high, i.e...
, ........- Polydesmiidae, Kobayashi 1940; ?late E- M Ord, C and E Asia; Polydesmia, Ordoceras
- ActinoceratidaeActinoceratidaeThe Actinoceriatidae is a family of actinocerids named by Saemann in 1853 for those that grew to have large shells with blunt apecies and large siphuncles with widely expanded segments and a generally arcuate endosiphucular canal system. Their range is from the upper Middle Ordovician to the Lower...
, Seamann 1853, ?late E, M Ord - E Sil. ActinocerasActinocerasActinoceras is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician.- Morphology:...
, Kochoceras, Paractinoceras, Saffordoceras, Troostoceras- Lambeoceratidae; LambeocerasLambeocerasLambeoceras is a rather large actinocerid with a convexly lenticular cross section from the Upper Ordovician of North America, and the sole representative of the family Lambeoceratidae.-Morphological Description:...
, - Huroniidae, HuroniaHuroniaHuronia is an actinocerid genus included in the Huroniidae along with Discoactinoceras and Huroniella,. Huronia is characterized by long siphuncle segments with the free part of the connecting rings only slightly inflated and by a narrow central canal and strongly curved radial canals located in...
, Huroniella, ? Discoactinoceras.
- Lambeoceratidae; Lambeoceras
- ArmenoceratidaeArmenoceratidaeArmenoceratidae is a family of early Paleozoic nautiloid cephalopods belonging to the Order Actinocerida.The Armenoceratidae, established by Troedsson is characterized by large, straight or slightly curved shells and large siphuncles with strongly expanded segments between the septa. Septal necks...
, Troedsson 1926; early M Ord - Sil. ArmenocerasArmenocerasArmenoceras is the principal genus of the Armenoceratidae, ranging from the late Whiterockian Stage in the early Middle Ordovician, through the remainder of the period and on into the Upper Silurian....
, Nybyoceras, Selkirkoceras, Elrodoceras- Gonioceratidae, late Mid Ord, N Am. GoniocerasGoniocerasGonioceras is an actinocerid with a broad, low shell; flattened ventrally, convexly rounded dorsally; top and bottom meeting at an acute angle along the sides. In most the shell is rather thin, especially along the lateral portion. The aperture is contracted...
(from early Armenoceratid)
- Gonioceratidae, late Mid Ord, N Am. Gonioceras
- Ormoceratidae, Seamann 1853, OrmocerasOrmocerasOrmoceras is an actinocerid genus of the family Ormoceratidae which is found in North America from the late Chazyan though the early Cincinnatian of the Middle and Upper Ordovician, but continued through the Devonian worldwide....
, Metarmenoceras, Parormoceras, Troedssonoceras........