The Choanoceratidae is a small, mono-generic,

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of extinct orthoceratoid

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

in the order

Orthocerida Orthocerida, from Ancient Greek ὀρθός (''orthós''), meaning "straight", and κέρας (''kéras''), meaning "horn", also known as the Michelinocerida, is an order of extinct Orthoceratoidea, orthoceratoid cephalopods that lived from the ...

that lived in what would be

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

during the middle

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 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 third and shortest period of t ...

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 longer juvenile portion and an inflated sho ...

. 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 cephalopod families Silurian animals Silurian extinctions Prehistoric animals of Europe Silurian first appearances Orthoceratoidea {{paleo-Nautiloidea-stub