The Choanoceratidae is a small, mono-generic,

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of extinct orthoceratoid

cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...

in the order

Orthocerida Orthocerida is an order of extinct Orthoceratoid cephalopods also known as the Michelinocerida that lived from the Early Ordovician () possibly to the Late Triassic (). A fossil found in the Caucasus suggests they may even have survived until ...

that lived in what would be

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

during the middle

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

from 428.2 to 426.2 mya, existing for approximately .Choanoceratidae
PaleoBiology Database

Taxonomy

Chaonoceratidae was named as the family for its sole member ''Choanoceras'' by Miller (1932) who, along with Flower (1941) regarded it as belonging to the

Ascocerida 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 longiconic juvenile portion and an inflate ...

. It became impossible to trace ''Choanoceras'' to the ascocerid lineage however, and based on closer affinities, it was assigned to the Michelinoceratida (Orthocerida equivalent) by Flower in 1962.R. H. Flower. 1962. Notes on the Michelinoceratida. State Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, Memoir 10, Part II

Morphology

''Choanoceras'' had a slender, very gently curved shell with a natural truncation where it discarded the

apical Apical means "pertaining to an apex". It may refer to: *Apical ancestor, refers to the last common ancestor of an entire group, such as a species (biology) or a clan (anthropology) *Apical (anatomy), an anatomical term of location for features loc ...

portion sometime during its life, somewhat resembling earlier ascocerids, with siphuncle segments that became gradually more expanded during growth. Nothing is known of the animal itself.

References

* ''Fossils'' (Smithsonian Handbooks) by David Ward Prehistoric nautiloid families Monogeneric mollusc families Silurian animals Silurian extinctions Prehistoric animals of Europe Silurian first appearances Orthoceratoidea {{paleo-Nautiloidea-stub