Pseudorthocerida
Encyclopedia
Pseudorthocerida are generally straight longiconic nautiloids with a subcentral to marginal cyrtochoanitic siphuncle
composed of variably expanded segments which may contain internal deposits that may develop into a continuous parietal lining.(Sweet 1964). Cameral deposits are common and concentrated ventrally. Apices typically have a slight to moderate exogastric curvature
The Pseudorthocerida are included in a broad in-group of generally orthoconic cephalopods known as the Orthoceratoidea (Kroger 2008) along with the Ascocerida
, Dissidocerida
, Lituitida
, and Orthocerida
. The Pseudorthocerida, Ascocerida, and Dissidocerida all have a cap-shaped apex, shared with Nautilids
and Actinocerids
, placing them in the "palcephalopoda". The Lituitida and Orthocerida share their spherical or bulbous apices with the Bactritida
and Ammonoidea, by which they are included in the "neocephalopoda
"
The Pseudorthocerida were among the last living orthoconic nautiloids. One family, the Trematoceratidae, survived into the Triassic
Period.
The Pseudorthoceratidae through Spyroceratidae are presented as subfamilies in Sweet (1964) and are included in the Pseudorthoceratidae sensu Sweet 1964). The Carbactinoceratidae are removed from the Actinocerida in Kroger and Mapes (2007)
and later Pseudorthoceratidae and Middle Ordovician
to Middle Silurian Proteoceratidae. Both have siphuncles that are partly cyrochoanitic with expanded segments and internal deposits but differ in the manner in which they develop.
Flower (1976) distinguished Middle Ordovician pseudorthocerids from Silurian and later pseudorthocerids on the basis of how the siphuncle changes during the life of the animal. The earlier Proteoceratidae begin cyrtochoantic with expanded segments and end up orthochoanitic with subcylindrical segments. As juveniles they are "pseudorthoceratoid", as mature individuals they are "orthoceratoid". In contrast the later Pseudorthoceratidae, begin orthochoanitic with subcylindrical segments and ontogenetically become cyrtochoanitic with expanded segments. As such they matured into "pseudorthoceratoids" from "orthoceratoid" junveniles. From this Flower (1976) concluded that the Ordovician and Silurian pseudorthocerids (sensu Sweet 1964) were derived from different orthocerids (Orthocerida) and were therefore polyphyletic
. As a result true pseudorthocerids were limited to the Pseudorthoceratidae while the earlier Ordovician look-a-likes were retained in the Orthocerida (Michelinocerida Flower)
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 variably expanded segments which may contain internal deposits that may develop into a continuous parietal lining.(Sweet 1964). Cameral deposits are common and concentrated ventrally. Apices typically have a slight to moderate exogastric curvature
The Pseudorthocerida are included in a broad in-group of generally orthoconic cephalopods known as the Orthoceratoidea (Kroger 2008) along with the Ascocerida
Ascocerida
The Ascocerida are comparatively small, bizarre nautiloids known only from Ordovician and Silurian sediments in Europe and North America, uniquely characterized by a deciduous conch consisting of a longiconic juvenile portion and an inflated breviconic adult portion that separate sometime in...
, Dissidocerida
Dissidocerida
The Dissidocerida comprise an order of Early Ordovician to the Early Silurian orthoceratoid cephalopods in which the siphuncle has a continuous lining or a longitudinal rod-like structure within....
, Lituitida
Lituitida
The Lituitida are the Lituitidae of the Treatise , reranked as an order and combined with other orthoceratoids.. They are considered to be more closely related to the Orthocerida than to the Ascocerida or Pseudorthocerida which are also included.Lituitids are characterized by smooth to annulate...
, 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...
. The Pseudorthocerida, Ascocerida, and Dissidocerida all have a cap-shaped apex, shared with Nautilids
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...
and Actinocerids
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...
, placing them in the "palcephalopoda". The Lituitida and Orthocerida share their spherical or bulbous apices with the Bactritida
Bactritida
The Bactritida form a small order of more or less straight-shelled cephalopods that first appeared during the Emsian Stage of the Devonian Period and persisted until the Carnian Stage of the Triassic Period...
and Ammonoidea, by which they are included in the "neocephalopoda
Neocephalopoda
Neocephalopods are a group of cephalopod mollusks that include the coleoids and all extinct species that are more closely related to extant coleoids than to the nautilus. In cladistic terms, it is the total group of Coleoidea...
"
The Pseudorthocerida were among the last living orthoconic nautiloids. One family, the Trematoceratidae, survived into the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
Period.
Current understanding
By current understanding the Pseudorthocerida contains the following families.- PseudorthoceratidaePseudorthoceratidaePseudorthoceratidae is an extinct family of actively mobile aquatic carnivorous cephalapods belonging to the subclass Orthoceratoidea endemic to what would be North America, Asia, and Europe during the Silurian living from 460.5—251 Ma, existing for approximately .In life, these animals may have...
- Cayutoceratidae
- PseudactinoceratidaePseudactinoceratidaePseudactinoceraidae is a family in the nautiloid cephalopod order, Pseudorthocerida, known from the Upper Devonian and Lower Carboniferous ....
- SpyroceratidaeSpyroceratidaeSpyroceratidae are defined as Pseudorthocerida with uniformly slender siphuncle segments, longer than wide, that contract sharply near either end, in which endosiphuncular deposits first form a compete annulus before fusing ventrally....
- CarbactinoceratidaeCarbactinoceratidaeCarbactinoceratidae is a family of extinct cephalopods with external shells that lived around 325 million years ago, during the Carboniferous period. They were the last group of orthocones to attain sizes exceeding one meter in length...
- Trematoceratidae
The Pseudorthoceratidae through Spyroceratidae are presented as subfamilies in Sweet (1964) and are included in the Pseudorthoceratidae sensu Sweet 1964). The Carbactinoceratidae are removed from the Actinocerida in Kroger and Mapes (2007)
Earlier perspectives
Pseudorthocerids were previously known as the Pseudorthocerataceae, a superfamily within the Orthocerida (Sweet 1964) which included the SilurianSilurian
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...
and later Pseudorthoceratidae and Middle Ordovician
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...
to Middle Silurian Proteoceratidae. Both have siphuncles that are partly cyrochoanitic with expanded segments and internal deposits but differ in the manner in which they develop.
Flower (1976) distinguished Middle Ordovician pseudorthocerids from Silurian and later pseudorthocerids on the basis of how the siphuncle changes during the life of the animal. The earlier Proteoceratidae begin cyrtochoantic with expanded segments and end up orthochoanitic with subcylindrical segments. As juveniles they are "pseudorthoceratoid", as mature individuals they are "orthoceratoid". In contrast the later Pseudorthoceratidae, begin orthochoanitic with subcylindrical segments and ontogenetically become cyrtochoanitic with expanded segments. As such they matured into "pseudorthoceratoids" from "orthoceratoid" junveniles. From this Flower (1976) concluded that the Ordovician and Silurian pseudorthocerids (sensu Sweet 1964) were derived from different orthocerids (Orthocerida) and were therefore polyphyletic
Polyphyly
A polyphyletic group is one whose members' last common ancestor is not a member of the group.For example, the group consisting of warm-blooded animals is polyphyletic, because it contains both mammals and birds, but the most recent common ancestor of mammals and birds was cold-blooded...
. As a result true pseudorthocerids were limited to the Pseudorthoceratidae while the earlier Ordovician look-a-likes were retained in the Orthocerida (Michelinocerida Flower)