Kutorginates (Kutorginata) are an extinct class of early

rhynchonelliform Rhynchonelliformea is a major subphylum and clade of brachiopods. It is roughly equivalent to the former Class (biology), class Articulata, which was used previously in brachiopod taxonomy up until the 1990s. These so-called articulated brachiop ...

("articulate")

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of 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 e ...

s. The class contains only a single order, Kutorginida (kutorginides). Kutorginides were among the earliest rhynchonelliforms, restricted to the lower-middle part of the

Cambrian Period The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...

Atdabanian Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxi ...

" tage 3to "Mayan" ate Miaolingian">Miaolingian.html" ;"title="ate Miaolingian">ate Miaolingian. Despite this short span of time, kutorginides were still a major order of Cambrian rhynchonelliforms during the lower Cambrian. Kutorginide diversity was highest up to the "Toyonian", though they began to decline in the mid-Cambrian even as other brachiopod orders (particularly Orthida, orthides and Acrotretida, acrotretides) diversified. A similar pattern of diversity loss is seen in obollelides, naukatides, and chileides, three other early rhynchonelliform orders contemporary with kutorginides.

Anatomy

Kutorginides typically have a ventribiconvex shell (both valves convex, the ventral valve moreso) and a strophic (straight) hinge line. Based on fossils of ''Nisusia'', the shell’s internal (secondary) layer appears to have a microstructure of

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

fibers. Internally, the valves are simpler than most other rhynchonelliforms. Though kutorginides are technically articulate, the hinge is not braced by teeth and sockets, but rather a system of thin ridges and deep furrows along the hinge line. Likewise,

cardinalia Rhynchonelliformea is a major subphylum and clade of brachiopods. It is roughly equivalent to the former class Articulata, which was used previously in brachiopod taxonomy up until the 1990s. These so-called articulated brachiopods have many ana ...

and dental plates are absent, with only a few subtle muscle scars in their place. The only other apparent structures are the mantle canals, which are pinnate in form (radiating, apart from the midline canals).

Posterior structures

The rear of the shell has a roughly

kite A kite is a tethered heavier than air flight, heavier-than-air craft with wing surfaces that react against the air to create Lift (force), lift and Drag (physics), drag forces. A kite consists of wings, tethers and anchors. Kites often have ...

- to

diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of e ...

-shaped profile. The

pseudodeltidium Rhynchonelliformea is a major subphylum and clade of brachiopods. It is roughly equivalent to the former class Articulata, which was used previously in brachiopod taxonomy up until the 1990s. These so-called articulated brachiopods have many ana ...

is voluminous, covering most of the delthyrium (ventral indentation) and taking up a large portion of the ventral valve from the rear. Conversely, the chilidium is rather low and undeveloped, leaving a large exposed

notothyrium Rhynchonelliformea is a major subphylum and clade of brachiopods. It is roughly equivalent to the former class Articulata, which was used previously in brachiopod taxonomy up until the 1990s. These so-called articulated brachiopods have many ana ...

(dorsal indentation). A small

pedicle Pedicle or pedicel may refer to: Human anatomy *Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures ...

foramen lies at the apex of the pseudodeltidium. Kutorginides also have another much larger and more enigmatic opening at the middle of the hinge line. This opening corresponds to the space encompassed by the notothyrium and the exposed portion of the delthyrium. The soft-tissue relevance of this opening has been a subject of debate, and recent evidence has argued for a more nuanced interpretation with variation within the class. Several kutorginides are preserved in

lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

n, elaborating on the structure and location of the pedicle relative to the two posterior openings. ''Kutorgina chengjiangensis'', from the

Chengjiang Lagerstätte The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized organ ...

of China, has a pedicle in the form of a thick annulated stalk. Despite its thickness, the pedicle is joined to the shell at the pseudodeltidium, strongly suggesting that it was originally derived from within the small pedicle foramen. The large posterior opening probably helped support strong diductor muscles in this interpretation. Several fossils of ''Nisusia sulcata,'' from the

Marjum Limestone The Marjum Formation is a Cambrian geological formation that overlies the Wheeler Shale in the House Range, Utah. It is named after its type locality, Marjum Pass, and was defined in 1908. The formation is known for its occasional preservation of ...

of Utah, tell a different story. Each fossil includes a distinctive

silicified In geology, silicification is a process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO2). Silica is a naturally existing and abundant com ...

tube within the large posterior opening. This tube has long been interpreted as a

coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name ...

, suggesting that kutorginides had a complete gut terminating at a gap in the rear of the shell. This condition is otherwise unknown in articulate brachiopods, and is more akin to inarticulates in the subphylum

Craniiformea 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. Cran ...

. However, modern brachiopods have very small fecal pellets, so the silicified tube may be better interpreted as an adult pedicle. The smaller foramen at the tip of the pseudodeltidium may be a remnant of a larval pedicle, later rendered redundant by a second pedicle developing at the hinge in adulthood. In this scenario, the pedicle of other rhynchonelliforms would be homologous to the larval pedicle of ''Nisusia sulcata''.

Subgroups

From '' The Treatise on Invertebrate Paleontology'' (Part H, Revised), unless stated otherwise: * Order Kutorginida ** Superfamily Kutorginoidea *** Family Kutorginidae **** '' Agyrekia'' Koneva 1979 ower-mid Cambrian ("Botomian" – "Amgan")**** '' Haupiria'' MacKinnon, 1983 id-Cambrian**** '' Kutorgina'' Billings, 1861 ower-mid Cambrian ("Atdabanian" – "Amgan")**** '' Schuchertina'' Walcott, 1905 id-Cambrian**** '' Yorkia'' Walcott, 1897 ower Cambrian** Superfamily Nisusioidea *** Family Nisusiidae **** '' Bellistrophia'' Holmer et al., 2019 id-Cambrian (Wuliuan)">Wuliuan.html" ;"title="id-Cambrian (Wuliuan">id-Cambrian (Wuliuan)**** ''Eoconcha'' Cooper, 1951 [lower-mid Cambrian] **** ''Khasagtina?'' Ushatinskaya, 1987 [lower Cambrian ("Tommotian"? – "Atdabanian")] **** ''Narynella'' Andreeva, 1987 ower Cambrian ("Toyonian") – mid-Cambrian**** ''

Nisusia Kutorginates (Kutorginata) are an extinct class of early rhynchonelliform ("articulate") brachiopods. The class contains only a single order, Kutorginida (kutorginides). Kutorginides were among the earliest rhynchonelliforms, restricted to the lo ...

'' Walcott, 1905 ower Cambrian ("Botomian") – mid-Cambrian**** '' Trematosia'' Cooper, 1967 ower Cambrian**''

Incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' genera: ***'' Anomalocalyx'' Brock, 1999 id-Cambrian (Drumian)">Drumian.html" ;"title="id-Cambrian (Drumian">id-Cambrian (Drumian)

Representative genera

''Kutorgina''

Some species of ''Kutorgina'' have a concavo-convex shell, with the smaller brachial (dorsal) valve dished in and the larger pedicle (ventral) valve broadly arched. The brachial valve has a rather prominent interarea at the back which is curved over by the prominent beak at the back of the pedicle valve. It includes the species ''Kutorgina elanica'' Malakhovskaya, 2013 and ''K. chengjiangensis'' Zhang et al. 2007, among many others. ''K. chengjiangensis'' preserves soft anatomy, including a pedicle, lophophore, and gut.

''Nisusia''

''Nisusia'' Walcott, 1905 (Walcott, 1889) is known from the Miaolingian-age Burgess Shale (~). It is a senior synonym to ''Orthisina alberta'' Walcott, 1889. The pedicle of ''Nisusia'' emerges from between its valves, as displayed by silicified material of ''N. sulcata'', though it still has an opening at the apex of the pedicle valve.

References

Kutorginata
* Moore, Lalicker, and Fischer. Invertebrate Fossils, ch 6 Brachiopoda. McGraw-Hill 1952.

External links

* Burgess Shale fossils Prehistoric brachiopod genera Paleontology in Washington (state) Burgess Shale animals Cambrian genus extinctions {{paleo-protostome-stub