Temporal range: Lower Cambrian to Recent
|Burmirhynchia jirbaensis (Jurassic, Israel)|
Rhynchonelliformea is a major subphylum and clade of brachiopods. It is equivalent to the former class Articulata, which was used previously in brachiopod taxonomy. Articulate brachiopods have many anatomical differences relative to "inarticulate" brachiopods of the subphyla Linguliformea and Craniformea. Articulates have hard calcium carbonate shells with tongue-and-groove hinge articulations (hence the name) and separate sets of simple opening and closing muscles.
The name, Rhynchoelliformea, which replaces Articulata, which is also a class of crinoids, comes from the family Rhynchonellidae, which however is no more representative of articulate brachiopods than any other group such as spirifers or strophomenids. It just happens to be the name chosen, based on an included taxon.
The main difference between the Rhynchonelliformea described in the Treatise Part H, revised 2000/2007, and the Articulata of the Treatise part H, 1965, lies in the groups included, their taxonomic positions and arrangements. The Rhynchonelliformea (Articulata revised) is divided into five classes: Obolellata, Kutorginata, Chileata, Strophomenata, and Rhynchonellata. The Strophomenata and Rhynchonellata are found living today; the Rhynchonellata as the major constituent of modern brachiopod faunas, the Stromphomenata as only a minor contributor. The Obolellata, Kutorginata, and Chileata are all extinct. The Obolellata and Kutorginata are restricted to the Cambrian, the Chileata ranges throughout the extent of the Paleozoic.
In the older classification of the Treatise (1965) the Class Articulata was divided into six orders, the Orthida, Pentamerida, Rhynchonellida, Spiriferida, Terebratulida, and Strophomenida. The Orthida, Pentamerida, Rhynchonellida, Spiriferida, and Terebratulida became combined as the Rhynchonellata. The Strophomenida became the Strophomenata with the addition of the Orthotetida and Billingsellida and separation of the Chileata. The Obolellata and Kutorginata were previously included in the Inarticulata, but have since been recognized as primitive articulates.
One of the more significant changes in the new classification is the splitting of the original Spiriferida into distinct and separate orders, the Spiriferida as revised, Atrypida, Athyridida, and Spiriferinida; each with its own derivation and phylogeny. Originally these were included as suborders within the Spiriferida which combined brachiopods with spiral (coiled spring-like) brachidia regardless of the orientation or the length of the hinge line or whether the shell was impunctate or punctate. The newer classification recognises the spiral brachidia being a matter of evolutionally convergence. The Athyridida is the Rostropiracea and the Spiriferinida is the Punctospiracea (suborders) of R.C, Moore in Moore, Lalicker, and Fischer, 1952.
The Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and extant invertebrate animals. The prehistoric invertebrates are described as to their taxonomy, morphology, paleoecology, stratigraphic and paleogeographic range. However, taxa with no fossil record whatsoever have just a very brief listing.
Spiriferida is an order of extinct articulate brachiopod fossils which are known for their long hinge-line, which is often the widest part of the shell. In some genera it is greatly elongated, giving them a wing-like appearance. They often have a deep fold down the center of the shell. The feature that gives the spiriferids their name ("spiral-bearers") is the internal support for the lophophore; this brachidium, which is often preserved in fossils, is a thin ribbon of calcite that is typically coiled tightly within the shell.
Craniata is a class of brachiopods originating in the Cambrian period and still extant today. It is the only class within the subphylum Craniiformea, one of three major subphyla of brachiopods alongside linguliforms and rhynchonelliforms. Craniata is divided into three orders: the extinct Craniopsida and Trimerellida, and the living Craniida, which provides most information on their biology. Living members of the class have shells which are composed of calcite, though some extinct forms my have aragonite shells. The shells are inarticulate and are usually rounded in outline. There is no pedicle, with the rear edge of the body cavity having the form of a smooth and flat wall perforated by the anus.
Mucrospirifer is a genus of extinct brachiopods in the class Rhynchonellata (Articulata) and the order Spiriferida. They are sometimes known as "butterfly shells". Like other brachiopods, they were filter feeders. These fossils occur mainly in Middle Devonian strata and appear to occur around the world, except in Australia and Antarctica.
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.
The Obolellata are a class of Rhynchonelliform brachiopods with two orders, Obolellida and Naukatida. They are essentially restricted to the lower-middle Cambrian.
Orthida is an extinct order of brachiopods which appeared during the Early Cambrian period and became very diverse by the Ordovician, living in shallow-shelf seas. Orthids are the oldest member of the subphylum Rhynchonelliformea, and is the order from which all other brachiopods of this group stem. Physically they are usually strophic, with well-developed interareas. They also commonly have radiating ribs, sulcus, and fold structures. Typically one valve, often the brachial valve, is flatter than the other. The interior structure of the brachial valves are usually simple. In shape they are sub-circular to elliptical, with typically biconvex valves.
Inarticulata was historically defined as one of the two classes of the phylum Brachiopoda and referred to those having no hinge. The other class was Articulata, meaning articulated — having a hinge between the dorsal and ventral valves. These classifications have now been superseded, see brachiopod classification.
The Craniidae are a family of brachiopods, commonly known as lamp shells. Although it belongs to a subdivision called the inarticulata which have shells where the mineral content consist of calcium phosphate, the Craniidae have shells that consist of calcium carbonate. Other special characteristics of this family are that no outgrowths are developed to form a hinge between both valves, nor is there any support for the lophophore. As adults, craniids either lived free on the ocean floor or, more commonly, were attached to a hard object with all or part of the ventral valve. All other brachiopods are supposed to have a stalk or pedicle, at least as an adolescent, but in craniids a pedicle is not known from any development stage.
Although the phylogenetic classification of non-vertebrate animals remains a work-in-progress, the following taxonomy attempts to be useful by combining both traditional (old) and new (21st-century) paleozoological terminology.
Strophomenida is an extinct order of articulate brachiopods which lived from the lower Ordovician period to the mid-Carboniferous period. Strophomenida is part of the extinct class Strophomenata, and was the largest known order of brachiopods, encompassing over 400 genera. Some of the largest and heaviest known brachiopod species belong to this class. Strophomenids were among the most diverse and abundant brachiopods during the Ordovician, but their diversity was strongly impacted at the Late Ordovician mass extinction. Survivors rediversified into new morphologies in the Silurian, only to be impacted once again at the Late Devonian mass extinction. They finally died out in the Carboniferous period.
Brachiopods, phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major groups are recognized, articulate and inarticulate. The word "articulate" is used to describe the tooth-and-groove features of the valve-hinge which is present in the articulate group, and absent from the inarticulate group. This is the leading diagnostic feature (fossilizable), by which the two main groups can be readily distinguished. Articulate brachiopods have toothed hinges and simple opening and closing muscles, while inarticulate brachiopods have untoothed hinges and a more complex system of muscles used to keep the two valves aligned. In a typical brachiopod a stalk-like pedicle projects from an opening in one of the valves near the hinges, known as the pedicle valve, keeping the animal anchored to the seabed but clear of silt that would obstruct the opening.
The Rhynchonellata is a class of Lower Cambrian to Recent articulate brachiopods that combines orders from within the Rhynchonelliformea with well developed pedicle attachment. Shell forms vary from those with wide hinge lines to beaked forms with virtually no hinge line and from generally smooth to strongly plicate. Most all are biconvex. Lophophores vary and include both looped and spiraled forms. Although morphologically distinct, included orders follow a consistent phylogenetic sequence.
Pentamerida is an order of biconvex, impunctate shelled, articulate brachiopods that are found in marine sedimentary rocks that range from the Middle Cambrian through the Devonian.
Athyridida is an order of Paleozoic brachiopods included in the Rhynchonellata, which makes up part of the articulate brachiopods.
Athyris is a brachiopod genus with a subequally biconvex shell that is generally wider than long and a range that extends from the Silurian into the Triassic. Athyris is the type genus for the Athyrididae, which belongs to the articulate order Athyridida. R.C. Moore (1952) gives a shorter range, from the Mid Devonian to the Lower Mississippian.
Strophomenata is an extinct class of brachiopods in the subphylum Rhynchonelliformea.
Productida is an extinct order of brachiopods in the extinct class Strophomenata. Members of Productida first appeared during the Silurian. They represented the most abundant group of brachiopods during the Permian period, accounting for 45-70% of all species. The vast majority of species went extinct during the Permian-Triassic extinction event, though a handful survived into the Early Triassic. Many productids are covered in hollow tubular spines, which are characteristic of the group. A number of functions for the spines have been proposed, including as a defensive mechanism against predators.
The following is a taxonomy of the Brachiopoda by Emig, Bitner & Álvarez (2019). There are over 400 living species and over 120 living genera of brachiopods classified within 3 classes and 5 orders, listed below.
Mesolobus is an extinct genus of brachiopod belonging to the order Productida and family Rugosochonetidae.