The taxonomicorderRhynchonellida is one of the two main groups of living articulatebrachiopods, the other being the order Terebratulida. They are recognized by their strongly ribbed wedge-shaped or nut-like shells, and the very short hinge line.
Ladogia sp., a rhynchonellid brachiopod from the Devonian of western Russia (side view).
The hinges come to a point, a superficial resemblance to many (phylogenetically unrelated) bivalvemollusk shells. The loss of the hinge line was an important evolutionary innovation, rhynchonellids being the first truly non-strophic shells with a purely internal articulation (teeth-sockets).
Strong radiating ribs are common in this group; and there are generally very strong plications or accordion-like folds on the sulcus (the long middle section) of the shell. This probably helps regulate the flow of water in and out of the shell. All rhynchonellids are biconvex (have a bulbous shell), and have a fold located in the brachial valve. This means that the commissure, the line between the two valves or shells, is zigzagged, a distinguishing characteristic of this group. The prominent beak of the pedicle valve usually overlaps that of the brachial valve, in order to allow the shell to open and close. There is usually a functional pedicle although the delthyrium may be partially closed.
Morphologically, the rhynchonellid has changed little since its appearance during the Ordovician period. It seems to have evolved from pentamerids, and in turn gave rise to the first atrypids and athyrids, both of which are characterized by the development of a complex spiral brachidium. Although much diminished by the terminal Paleozoic extinction, it experienced a revival during the Early Jurassic period, and became the most abundant of all brachiopods during the Mesozoic Era.
Classification
This classification down to the level of genera is based on Kazlev[1] and Emig.[2]
^M. Alan Kazlev. . Archived from the original on March 13, 2006. Retrieved March 10, 2006.
^Christian C. Emig. (PDF). Archived from the original (PDF) on May 13, 2006. Retrieved March 10, 2006.
External links
March 22, 2023
rhynchonellida, taxonomic, order, main, groups, living, articulate, brachiopods, other, being, order, terebratulida, they, recognized, their, strongly, ribbed, wedge, shaped, like, shells, very, short, hinge, line, temporal, range, upper, ordovician, recent, p. The taxonomic order Rhynchonellida is one of the two main groups of living articulate brachiopods the other being the order Terebratulida They are recognized by their strongly ribbed wedge shaped or nut like shells and the very short hinge line RhynchonellidaTemporal range Upper Ordovician Recent PreꞒ Ꞓ O S D C P T J K Pg NRhynchotrema dentatum a rhynchonellid brachiopod from the Cincinnatian Upper Ordovician of SE Indiana Scientific classificationKingdom AnimaliaPhylum BrachiopodaClass RhynchonellataOrder RhynchonellidaKuhn 1949SubgroupsSee text Hemithiris psittacea a living rhynchonellide Ladogia sp a rhynchonellid brachiopod from the Devonian of western Russia side view The hinges come to a point a superficial resemblance to many phylogenetically unrelated bivalve mollusk shells The loss of the hinge line was an important evolutionary innovation rhynchonellids being the first truly non strophic shells with a purely internal articulation teeth sockets Strong radiating ribs are common in this group and there are generally very strong plications or accordion like folds on the sulcus the long middle section of the shell This probably helps regulate the flow of water in and out of the shell All rhynchonellids are biconvex have a bulbous shell and have a fold located in the brachial valve This means that the commissure the line between the two valves or shells is zigzagged a distinguishing characteristic of this group The prominent beak of the pedicle valve usually overlaps that of the brachial valve in order to allow the shell to open and close There is usually a functional pedicle although the delthyrium may be partially closed Morphologically the rhynchonellid has changed little since its appearance during the Ordovician period It seems to have evolved from pentamerids and in turn gave rise to the first atrypids and athyrids both of which are characterized by the development of a complex spiral brachidium Although much diminished by the terminal Paleozoic extinction it experienced a revival during the Early Jurassic period and became the most abundant of all brachiopods during the Mesozoic Era Classification EditThis classification down to the level of genera is based on Kazlev 1 and Emig 2 Extant subgroups Superfamily Pugnacoidea Family Basiliolidae Subfamily Acanthobasiliolinae Acanthobasiliola Subfamily Basiliolinae Basiliola Basiliolella Eohemithiris Rhytirhynchia Subfamily Uncertain Striarina Superfamily Dimerelloidea Family Cryptoporidae Aulites Cryptopora Superfamily Norelloidea Family Frieleiidae Subfamily Freileiinae Frieleia Compsothyris Grammetaria Sphenarina Subfamily Hispanirhynchiinae Abyssorhynchia Hispanirhynchia Manithyris Parasphenarina Subfamily Neorhynchiinae Neorhynchia Family Tethyrhynchiidae Tethyrhynchia Superfamily Hemithiridoidea Family Hemithyrididae Hemithiris Pemphixina Family Notosariidae NotosariaExtinct Subgroups Superfamily Ancistrorhynchoidea Superfamily Rhynchotrematoidea Superfamily Uncinuloidea Superfamily Camarotoechioidea Superfamily Rhynchotetradoidea Superfamily Lambdarinoidea Superfamily Wellerelloidea Superfamily Rhynchoporoidea Superfamily StenoscismatoideaReferences Edit M Alan Kazlev Order Rhynchonellida Archived from the original on March 13 2006 Retrieved March 10 2006 Christian C Emig Systematics of extant brachiopod taxa PDF Archived from the original PDF on May 13 2006 Retrieved March 10 2006 External links EditPhylum Brachiopoda Retrieved from https en wikipedia org w index php title Rhynchonellida amp oldid 1078131923, wikipedia, wiki, book, books, library,
