Acrotretida is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

of linguliform brachiopods in the class

Lingulata Lingulata is a class of brachiopods, among the oldest of all brachiopods having existed since the Cambrian period (). They are also among the most morphologically conservative of the brachiopods, having lasted from their earliest appearance to the ...

. They lived from the Lower Cambrian to the Middle Devonian, with their peak diversity from the

Middle Cambrian Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (di ...

to the Ordovician. Acrotretida contains the sole

superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

Acrotretoidea. Many acrotretides have a tall and conical ventral valve with a pedicle opening at the apex, while the dorsal valve was convex to a much lesser degree. Based on preserved muscle scars, the lateral muscles are shifted back and condensed into large bundles of

tendons A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...

. These replace the stout, column-like central muscles, which are present in other linguliforms but apparently absent in acrotretides. The larval shell, which is retained near the pedicle opening, has a strongly pitted texture. The adult shell is smooth and has a rounded outline, and is

phosphatic In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosphor ...

like other linguliforms.

Subgroups

* Superfamily Acrotretoidea Schuchert, 1893 ** Family Acrotretidae Schuchert, 1893 (Lower Cambrian - mid-

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 ...

Wenlock">Wenlock_Epoch.html" ;"title="nowiki/>Wenlock Epoch">Wenlock ** Family Biernatidae Holmer, 1989 (Lower Ordovician [Tremadocian, Tremadoc] - Middle Devonian) ** Family Ceratretidae Rowell, 1965 (Cambrian) ** Family Curticiidae Walcott & Schuchert, 1908 (

Upper Cambrian The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three ...

) ** Family Eoconulidae Rowell, 1965 ( Middle Ordovician nowiki/>Arenig">Arenig.html" ;"title="nowiki/>Arenig">nowiki/>Arenig- Upper Ordovician [Ashgill (age), Ashgill]) ** Family Ephippelasmatidae Rowell, 1965 (Upper Cambrian - Upper Ordovician [Ashgill]) ** Family Scaphelasmatidae Rowell, 1965 (Middle Cambrian nowiki/>Amgan">Amgan.html" ;"title="nowiki/>Amgan">nowiki/>Amgan- Upper Silurian) ** Family Torynelasmatidae Rowell, 1965 (Middle Ordovician [Arenig] - Silurian) * Incertae sedis ** ''Craniotreta'' Termier & Monod, 1978 ** ''Dzhagdicus'' Sobolev, 1992 ** '' Schizotretoides'' Termier & Monod, 1978

References

External links

AccessScience entry
Prehistoric brachiopods Brachiopod orders Lingulata {{brachiopod-stub