Baltoceratidae
Encyclopedia
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 .
by Flower and Kummel (1950) where it was retained by Unklesbay and Young (1956), again by Flower (1964)
, and by Furnish and Glenister in Teichert et al (1964). Flower(1964) included the Baltoceratidae in the ellesmeroceratid suborder Ellesmeroceratina.
Further study of baltoceratid interiors, namely regarding the generally thin connecting rings and lack of siphuncular diaphragms, showed they are distinct from the typical ellesmerocerids and belong, as the ancestral group, to the Orthocerida where assigned by Kroger et al (2007)
composed of orthochoantic Septum (mollusc anatomy)septal necks and thin connecting rings, free of diaphragms and which in advanced forms becomes more central in position. Septa are close spaced, resulting in short camerae and may form shallow ventral lobes. Cameral deposits are normal which develop apically and more ventrally.
Two stocks are found within the Baltoceratidae, those with a calcareous rod secreted on the lower surface of the inside of the siphuncle known as "rod-bearing" and those without, in which the interior of the siphuncle tube is empty, known as "vacuosiphonate". Empty siphuncled forms, the vacuosiphonate, gave rise to the Michelinoceratidae, commonly known as the Orthoceratidae, which has its beginning in the lower Cassinian
stage in the latter part of the Lower Ordovician. Rod bearing forms gave rise to the Troedsonnellidae with early members, Buttsoceras and Tajaroceras
found in the upper Cassinian.
The Baltoceratidae and Orthoceratidae both have a spherical apex that lacks a cicatrix, and similar, two-layered thin connecting rings which clearly places the Baltoceratidae in the Orthocerida as well. Furthermore the Baltoceratidae are restricted to forms with a siphuncle that is tubular or slightly expanded within the chambers, excluding genera with a more ellesmeroceratid aspect in which connecting rings thicken inwardly, such as Amsleroceras, Cyptendoceras
, and Rioceras
.
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
during the 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...
living from about 480–460 mya, existing for approximately .
Taxonomy
Baltoceratidae was named by Kobayashi (1935) and assigned to the EllesmeroceratidaEllesmerocerida
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:...
by Flower and Kummel (1950) where it was retained by Unklesbay and Young (1956), again by Flower (1964)
, and by Furnish and Glenister in Teichert et al (1964). Flower(1964) included the Baltoceratidae in the ellesmeroceratid suborder Ellesmeroceratina.
Further study of baltoceratid interiors, namely regarding the generally thin connecting rings and lack of siphuncular diaphragms, showed they are distinct from the typical ellesmerocerids and belong, as the ancestral group, to the Orthocerida where assigned by Kroger et al (2007)
Diagnosis
The Baltorceratidae are characterized by dominantly straight, slender, smooth shells with a moderately large ventral siphuncleSiphuncle
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 orthochoantic Septum (mollusc anatomy)septal necks and thin connecting rings, free of diaphragms and which in advanced forms becomes more central in position. Septa are close spaced, resulting in short camerae and may form shallow ventral lobes. Cameral deposits are normal which develop apically and more ventrally.
Two stocks are found within the Baltoceratidae, those with a calcareous rod secreted on the lower surface of the inside of the siphuncle known as "rod-bearing" and those without, in which the interior of the siphuncle tube is empty, known as "vacuosiphonate". Empty siphuncled forms, the vacuosiphonate, gave rise to the Michelinoceratidae, commonly known as the Orthoceratidae, which has its beginning in the lower Cassinian
Cassinian
The Cassinian is the latest age of the Canadian Epoch when thought of temporally and the uppermost stage of the Canadian Series when thought of stratigraphically...
stage in the latter part of the Lower Ordovician. Rod bearing forms gave rise to the Troedsonnellidae with early members, Buttsoceras and Tajaroceras
Tajaroceras
Tejaroceras is an extinct slender cephalopod from the uppermost Lower Ordovician of western North America, belonging to the Orthocerid family Troedssonellidae....
found in the upper Cassinian.
The Baltoceratidae and Orthoceratidae both have a spherical apex that lacks a cicatrix, and similar, two-layered thin connecting rings which clearly places the Baltoceratidae in the Orthocerida as well. Furthermore the Baltoceratidae are restricted to forms with a siphuncle that is tubular or slightly expanded within the chambers, excluding genera with a more ellesmeroceratid aspect in which connecting rings thicken inwardly, such as Amsleroceras, Cyptendoceras
Cyptendoceras
Cyptendoceras is an extinct nautiloid cephalopod included in the family Ellesmeroceratidae that lived in what would be North and South America during the latter part of the Early Ordovician from about 475 - 472 mya, existing for approximately .-Taxonomy:Cyptendoceras was named by Ulrich and Foerste...
, and Rioceras
Rioceras
Rioceras is an extinct orthocerid cephalapod genus 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.-Taxonomy:...
.