Miaolingian

The Miaolingian is the third Series of the Cambrian period, and was formally named in 2018.[1] It lasted from about 509 to 497 million years ago and is divided into 3 stages: the Wuliuan, the Drumian, and the Guzhangian. The Miaolingian is preceded by the unnamed Cambrian Series 2 and succeeded by the Furongian series.[2]

Definition

The lower boundary of the Miaolingian has the same definition as that of the Wuliuan. This boundary was formally defined by the ICS in 2018.

A number of proposals for fossils and type sections were made. The most promising fossil markers were seen to be the respective first appearances of either trilobite species Ovatoryctocara granulata or Oryctocephalus indicus.[3] Either species should have an age close to 509 million years ago.[2] The Miaolingian-Furongian boundary has the same definition as the Paibian stage. It is defined as the first appearance of Glyptagnostus reticulatus around 497 million years ago.[2]

Subdivision

The Miaolingian is subdivided into the following stages:[2]

Epoch Stage Age (mya)
Furongian
Stage 10 489.5
Jiangshanian 494
Paibian 497
Miaolingian
Guzhangian 500.5
Drumian 504.5
Wuliuan 509
Series 2
Stage 4 514
Stage 3 521

References

  1. ^ http://www.stratigraphy.org/ICSchart/ChronostratChart2018-08.pdf
  2. ^ a b c d "GSSP Table - Paleozoic Era". Retrieved 15 November 2012.
  3. ^ Gozalo, Rodolfo; Álvarez, María Eugenia Dies; Vintaned, José Antonio Gámez; Zhuravlev, Andrey Yu.; Bauluz, Blanca; Subías, Ignacio; Chirivella Martorell, Juan B.; Mayoral, Eduardo; Gursky, Hans-Jürgen; Andrés, José Antonio; Liñán, Eladio (1 December 2011). "Proposal of a reference section and point for the Cambrian Series 2-3 boundary in the Mediterranean subprovince in Murero (NE Spain) and its intercontinental correlation". Geological Journal. 48: 142–155. doi:10.1002/gj.1330.
Aglaspidida

Aglaspidida is an extinct order of aquatic arthropods that were once regarded as primitive chelicerates. However, anatomical comparisons demonstrate that the aglaspidids cannot be accommodated within the chelicerates, and that they lie instead within the Artiopoda, thus placing them closer to the trilobites. Aglaspidida contains the subgroups Aglaspididae and Tremaglaspididae, which are distinguished by the presence of acute/spinose genal angles and a long spiniform tailspine in the Aglaspididae.Aglaspidid fossils are found in North America (upper Mississippi valley, Missouri and Utah), Europe, Australia, and China. Certain other artiopods are believed to be closely related to the aglaspidids, including the order Strabopida, which includes the genera Strabops, Paleomerus, Parapaleomerus, and possibly Khankaspis.

Agnostus

Agnostus is a genus of agnostid trilobites that lived during the upper Middle Cambrian–lower Upper Cambrian (about 506 to 492 million years ago). It is the type genus of the family Agnostidae. It is subdivided into two subgenera, Agnostus and Homagnostus.

Cambrian Series 2

Cambrian Series 2 is the unnamed 2nd series of the Cambrian. It lies above the Terreneuvian series and below the Miaolingian. Series 2 has not been formally defined by the International Commission on Stratigraphy, lacking a precise lower boundary and subdivision into stages. The proposed lower boundary is the first appearance of trilobites which is estimated to be around 521 million years ago.

Condylopygidae

The Condylopygidae are a family of very small trilobites, that lived during the Middle Cambrian, and has been found in Canada (Newfoundland and Nova Scotia), the Czech Republic, Germany, France, Spain, England, Wales, Sweden, and the Russian Federation (Siberia). They uniquely differ from all other Agnostina in having the frontal lobe of the central raised area of the headshield (or glabella) wider than the rear lobe. The Condylopygidae are the only family assigned to the Condylopygoidea superfamily.

Drumian

The Drumian is a stage of the Miaolingian Series of the Cambrian. It succeeds the Wuliuan and precedes the Guzhangian. The base is defined as the first appearance of the trilobite Ptychagnostus atavus around 504.5 million years ago. The top is defined as the first appearance of another trilobite Lejopyge laevigata around 500.5 million years ago.

The GSSP is defined in the Drumian section (39.5117°N 112.9915°W / 39.5117; -112.9915) in the Drum Mountains, Millard County, Utah, United States. The stage was also named after the Drum Mountains. The section is an outcrop of the Wheeler Formation, a succession of calcareous shales. The precise base of the Drumian is a laminated limestone 62 m (203 ft) above the base of the Wheeler Formation.

Furongian

The Furongian is the fourth and final series of the Cambrian. It lasted from 497 to 485.4 million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian stage. It is subdivided into three stages: the Paibian, Jiangshanian and the unnamed 10th stage of the Cambrian.

Guzhangian

The Guzhangian is an uppermost stage of the Miaolingian Series of the Cambrian. It follows the Drumian Stage and precedes the Paibian Stage of the Furongian Series. The base is defined as the first appearance of the trilobite Lejopyge laevigata around 500.5 million years ago. The Guzhangian-Paibian boundary is marked by the first appearance of the trilobite Glyptagnostus reticulatus around 497 million years ago.The name Guzhangian is derived from Guzhang County in Hunan Province of China.

The GSSP is defined in the Huaqiao Formation in Hunan, China. The precise base of the Guzhangian is a limestone layer 121.3 m above the base Huaqiao Formation at the Louyixi section (28.7200°N 109.9647°E / 28.7200; 109.9647), where Lejopyge laevigata has its first appearance.

Hemichordate

Hemichordate is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include two main classes: Enteropneusta (acorn worms), and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera pelagica. The extinct class Graptolithina is closely related to the pterobranchs.Acorn worms are solitary worm-shaped organisms. They generally live in burrows (the earliest secreted tubes) and are deposit feeders, but some species are pharyngeal filter feeders, while the family Torquaratoridae are free living detritivores. Many are well known for their production and accumulation of various halogenated phenols and pyrroles. Pterobranchs are filter-feeders, mostly colonial, living in a collagenous tubular structure called a coenecium.

Lejopyge laevigata

Lejopyge laevigata is a species of agnostid trilobite belonging to the genus Lejopyge. It existed during the Guzhangian to the Paibian Age (around 500.5 to 497 million years ago) of the Cambrian. It has a cosmopolitan distribution and is an important index fossil in biostratigraphy.

Nectocaris

Nectocaris pteryx is a species of possible cephalopod known from the "early Cambrian" (Series 2) Emu Bay Shale and Chengjiang biota, the "middle Cambrian" (Mioalingian, Wuliuan) Burgess Shale.

Nectocaris was a free-swimming, predatory or scavenging organism. This lifestyle is reflected in its binomial name: Nectocaris means "swimming shrimp" (from the Ancient Greek νηκτόν, nekton, meaning "swimmer" and καρίς, karis, "shrimp"; πτέρυξ, pteryx, means "wing"). Two morphs are known: a small morph, about an inch long, and a large morph, anatomically identical but around four times longer.

The closely related Ordovician taxon Nectocotis is a second genus, closely resembling Nectocaris, but possessing an internal skeletal element.

Nepeidae

The Nepeidae are a family of trilobites, that lived during the late Middle Cambrian - earliest Upper Cambrian in what are today Australia, Antarctica, China and New Zealand. The Nepeidae can be recognized by a vaulted area between the front of the glabella and the frontal border, eye ridges that extend outward and slightly forward from the front of the glabella, and fixed cheeks that cut into the free cheeks at the inside of the eye, and that extend backwards, forming the inner base of the genal spines. The genal spines, however, are part of the free cheeks and extend backward at least half the length of the thorax. The thorax has at least 20 segments. The tail shield (or pygidium) is small.

Odontopleurida

Odontopleurida is an order of very spinose trilobites closely related to the trilobites of the order Lichida. Some experts group the Odontopleurid families, Odontopleuridae and Damesellidae, within Lichida. Odontopleurids tend to have convex, bar-shaped cephalons, and lobed, knob-shaped glabella that extend to, or almost to the anterior margin. Many, if not almost all odontopleurids have long spines that are derived either from the margins of the exoskeleton, or from granular or tubercular ornamentation, or both. Many odontopleurids are so spinose so as to be described as having "spines on (their) spines." Odontopleurids have 8 to 13 thoracic segments, with Odontopleuridae odontopleurids having no more than 10, and Damesellidae odontopleurids having no more than 13. The pygidium tends to be very small, and invariably has long spines emanating from it in all known genera.

Genera of Damesellidae are restricted to Middle to Upper Cambrian marine strata, and may represent a transition between Cambrian-aged lichids, and odontopleurids of Odontopleuridae. The odontopleurids of Odontopleuridae first appear in the Upper Cambrian, and go extinct before the end of the Frasnian stage of the late Devonian.

Oryctocephalus indicus

Oryctocephalus indicus is a species of corynexochid trilobite from the Cambrian. Its first appearance is proposed for the lower boundary of the Wuliuan, which corresponds to the beginning of the Miaolingian (The other proposal was Ovatoryctocara granulata). The species was first described by the British paleontologist Frederick Richard Cowper Reed in 1910 as Zacanthoides indicus. It was transferred to the genus Oryctocephalus by the American paleontologist Charles Elmer Resser in 1938.

Ottoia

Ottoia is a stem-group archaeopriapulid worm known from Cambrian fossils. Although priapulid-like worms from various Cambrian deposits are often referred to Ottoia on spurious grounds, the only clear Ottoia macrofossils come from the Burgess Shale of British Columbia, which was deposited 508 million years ago. Microfossils extend the record of Ottoia throughout the Western Canada Sedimentary Basin, from the mid- to late- Cambrian.

Ptychagnostidae

Ptychagnostidae is a family of agnostid trilobites from the 5th Stage to the Paibian Age of the Cambrian (509 to 497 million years ago). The family includes several important index fossils.

Redlichiida

Redlichiida is an order of trilobites, a group of extinct marine arthropods. Species assigned to the order Redlichiida are among the first trilobites to appear in the fossil record, about halfway during the Lower Cambrian. Due to the difficulty to relate sediments in different areas, there remains some discussion, but among the earliest are Fallotaspis (suborder Olenellina), and Lemdadella (suborder Redlichiina), both belonging to this order. The first representatives of the orders Corynexochida and Ptychopariida also appear very early on and may prove to be even earlier than any redlichiid species. In terms of anatomical comparison, the earliest redlichiid species are probably ancestral to all other trilobite orders and share many primitive characters. The last redlichiid trilobites died out before the end of the Middle Cambrian.

Wiwaxia

Wiwaxia is a genus of soft-bodied animals that were covered in carbonaceous scales and spines that protected it from predators. Wiwaxia fossils – mainly isolated scales, but sometimes complete, articulated fossils – are known from early Cambrian and middle Cambrian fossil deposits across the globe. The living animal would have measured up to 5 cm (2 inch) when fully grown, although a range of juvenile specimens are known, the smallest being 2 millimetres (0.079 in) long.Wiwaxia's affinity has been a matter of debate: researchers were long split between two possibilities. On the one hand, its rows of scales looked superficially similar to certain scale worms (annelids); conversely, its mouthparts and general morphology suggested a relationship to the shell-less molluscs. More recently, evidence for a molluscan affinity has been accumulating, based on new details of Wiwaxia's mouthparts, scales, and growth history.The proposed clade Halwaxiida contains Wiwaxia as well as several similar Cambrian animals.

Wuliuan

The Wuliuan stage is the fifth stage of the Cambrian, and the first stage of the Miaolingian Series of the Cambrian. It was formally defined by the ICS in 2018.

Its base is defined by the first appearance of the trilobite species Oryctocephalus indicus; it ends with the beginning of the Drumian stage, marked by the first appearance of the trilobite Ptychagnostus atavus around 504.5 million years ago.The 'golden spike' that formally defines the base of the period is driven into the Wuliu-Zengjiayan section of the Kaili formation, near Balang Village in the Miaoling Mountains, Guizhou, China.

Cenozoic era
(present–66.0 Mya)
Mesozoic era
(66.0–251.902 Mya)
Paleozoic era
(251.902–541.0 Mya)
Proterozoic eon
(541.0 Mya–2.5 Gya)
Archean eon (2.5–4 Gya)
Hadean eon (4–4.6 Gya)

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