Orthoceras is a genus of extinct nautiloid cephalopod restricted to Middle Ordovician-aged marine limestones of the Baltic States and Sweden. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera, Orthocerus or Orthoceros.
Orthoceratidae is an extinct family of actively mobile carnivorous cephalopods, subclass Nautiloidea, that lived in what would be North America, Europe, Asia, Africa, and Australia from the Ordovician through Triassic from 490—203.7 mya, existing for approximately 286.4 million years.
Orthocerida, also known as the Michelinocerida, is an order of extinct orthoceratoid cephalopods 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 the Eocene fossil Antarcticeras is sometimes considered a descendant of the orthocerids although this is disputed. They were most common however from the Ordovician to the Devonian.
The Bactritida are a small order of more or less straight-shelled (orthoconic) cephalopods that first appeared during the Emsian stage of the Devonian period with questionable origins in the Pragian stage before 409 million years ago, and persisted until the Carnian pluvial event in the upper middle Carnian stage of the Triassic period. They are considered ancestors of the ammonoids, as well as of the coleoids.
The Ascocerida are comparatively small, bizarre Orthoceratoids known only from Ordovician and Silurian sediments in Europe and North America, uniquely characterized by a deciduous conch consisting of a longer juvenile portion and an inflated short adult portion that separate sometime in maturity.
Kionoceras is an extinct nautiloid cephalopod genus included in the orthocerid family Kionoceratidae with scattered worldwide distribution from the Middle Ordovician to the Lower Permian. Kionoceratids are orthocerids with prominent longitudinal ornamentation on their shells, sometimes augmented by secondary transverse ornamentation. Orthocerids are, of course, prehistoric nautiloides with generally straight and elongate shells, mostly with central or subcentral siphuncles.
Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, existing for approximately 20 million years.
Geisonoceratidae is an extinct family of orthoceroid cephalopods endemic to what would be Asia, Europe, and North America from the Middle Ordovician to the Middle Devonian living from about 470—380 mya, existing for approximately 90 million years. With the possible addition of an Early Cretaceous orthocerid from the western Caucasus the range of this group increases dramatically to some 350 million years, thus making it one of the longest lived families of the Nautiloidea.
Proteoceratidae is an extinct family of actively mobile aquatic carnivorous cephalopods belonging to the subclass Orthoceratoidea endemic to what would be Asia, Australia, Europe, South America and North America during the Ordovician living from 490—445.6 Ma, existing for approximately 44.4 million years.
Pseudorthoceratidae is an extinct family of actively mobile aquatic carnivorous cephalopods 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 209.5 million years.
Eosomichelinoceras is an extinct genus from the actively mobile carnivorous cephalopod family Baltoceratidae that lived in what would be Asia and South America during the Ordovician from 461—452 mya, existing for approximately 9 million years.
Rioceras is an extinct genus of orthocerid cephalopods of the family Baltoceratidae that lived in what would be North America during the Early Ordovician from 480—472 mya, existing for approximately 8 million years.
Sactoceras is an extinct nautiloid cephalopod that lived during the Ordovician and Silurian in what would become North America, Europe, and Asia.
Orthoceratoidea is a major subclass of nautiloid cephalopods. Members of this subclass usually have orthoconic (straight) to slightly cyrtoconic (curved) shells, and central to subcentral siphuncles which may bear internal deposits. Orthoceratoids are also characterized by dorsomyarian muscle scars, extensive cameral deposits, and calciosiphonate connecting rings with a porous and calcitic inner layer.
The Orthocerataceae is a superfamily of orthocerid cephalopods that lived from the late Early Ordovician to the Early Cretaceous, but is no longer in general use.
Kionoceratidae is a family in the Orthocerida, proposed by Hyatt in 1900 for genera characterized by prominent ornamentation in the form of longitudinal ribs, ridges, or lirae, or combinations thereof, sometimes with similar transverse ornament or faint transverse annulations.
Protcycloceratidae is an extinct family of slender, commonly annulate, members of the cephalopod order Ellesmerocerida that lived during the Early Ordovician.
Murrayoceras is a nautilid cephalopod included in the orthocerid family Baltoceratidae, widespread in the Middle Ordovician of North America, characterized by a depressed orthoconic shell with a subtriangular cross section and flattened venter and a proportionally large ventral siphuncle, 0.15 to 0.3 the dorso-ventral shell diameter. Septa are close spaced with sutures forming broad lobes on the upper flanks and ventral surface.
Braulioceras is a smooth, orthoconic orthocerid with very close spaced septa added to the Sactorthoceratidae in 2007. The type species, Braulioceras sanjuanense comes from the Middle Ordovician of the San Juan Formation, Argentine Precordillera.
Ascoceratidae is a family of Ascocerida, bizarre orthoceratoid cephalopods, with longiconic, deciduous early growth stages which undergo period truncation and an inflated breviconic mature ascoceroid stage. The Ascoceratidae are divided into two, unequal subfamilies.
