Redlichiida

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Redlichiida
Eoredlichia intermedia from the Maotianshan schist, China

Eoredlichia intermedia from the Maotianshan schist , China

Temporal occurrence
Cambrian
542 to 490 million years
Locations
  • Worldwide
Systematics
without rank: Bilateria
without rank: Primordial mouths (protostomia)
Over trunk : Molting animals (Ecdysozoa)
Trunk : Arthropod (arthropoda)
Class : Trilobites (Trilobita)
Order : Redlichiida
Scientific name
Redlichiida
Richter , 1932

The Redlichiida are one of the nine orders of the extinct trilobites (Trilobita). Together with the Agnostida , the Corynexochida and the Ptychopariida , they are one of the four older trilobite orders that appeared as early as the Lower Cambrian .

etymology

The order of the Redlichiida was described scientifically for the first time in 1932 by the German paleontologist Rudolf Richter and named in honor of the Austrian geologist Karl August Redlich .

description

( Morphological terms are explained in more detail in the article Trilobites )

Redlichiida have a primitive appearance. Their cephalon (head shield) is large and semicircular, the glabella usually elongated, clearly segmented and usually widening towards the front. The strong cheek spines are an extension of the tubular, reinforced head shield edge. The hypostome is usually positioned conterminant. The rostral plate is usually quite wide. Their eyes are elongated, prominent, and sickle-shaped; they are accompanied by a distinct back-shaped bulge - the eye ridges - which extends to the front edge of the glabella. The thorax (breastplate) consists of many segments (there can be more than 90), the length of which decreases steadily towards the pygidium (tail shield); the pleura usually end in points. Sometimes it is possible to divide the thorax into a wider prothorax and a narrower ophistothorax (as is the case with the Emuelloidea, for example). The tiny pygidium often consists of only one or very few segments.

Redlichiida are very often armed with spines - these can attach to the head shield (cheek spines), the glabella, the tail and the thoracic segments (pleural spines). In contrast to other trilobite orders, Redlichiida were most likely unable to curl up for defense purposes.

The Olenelliden family have spines on the third breast segment as a distinguishing feature. In some finds, extensions such as legs, antennae and gills etc. have also been preserved. In number, arrangement and type these follow characteristic patterns for trilobites.

Distribution and occurrence

Redlichiida are common fossils with worldwide distribution in the fauna communities of the Lower Cambrian . They were found in two known conservation deposits - in Emu Bay Shale in the state of South Australia ( Kangaroo Island ) and in the Chengjiang Faunal Community in the People's Republic of China .

Fauna provinces

Within the Redlichiida, representatives of the Redlichiina suborder occur only in Cambrian strata groups outside Laurentia; they can be found in the Acadobaltic Fauna Province - Avalonia , Baltica and Western Gondwana - as well as in the Oriental Fauna Province of Eastern Gondwana. In contrast to the Olenellidae family, they have facial sutures and their fossilizations are often accompanied by the so-called librigenae ("free cheeks").

The Olenelliden family, on the other hand, is restricted to the Cambrian continent Laurentia ( North American Fauna Province - North America and associated areas). Olenellidae are quite common and also define the extent of Laurentia at that time. Their sudden disappearance defines the border between Lower and Central Cambrian in their area of ​​distribution. Olenellide do not have a face seam.

Between the Olenellids and the Redlichiina there is a clearly pronounced exclusivity of their occurrence, only in Morocco and in western Mongolia do both faunas occur together. Strongly endemic genera of the Redlichiina also allow a further subdivision of the Oriental Fauna Province into the following sub-provinces:

Development history

Redlichiida are the first trilobites ever to appear in the fossil record . The oldest known trilobite comes from the Redlichiida family Fallotaspidae . Most scientists are of the opinion that the common ancestor of all other trilobite orders is to be found in the order Redlichiida or in their subordination Redlichiina - the agnostids are an exception. It is usually assumed that the orders Corynexochida and Ptychopariida developed from the Redlichiina during the Lower Cambrian and that the Lichida then later emerged during the Central Cambrian either from the Redlichiida or from the Corynexochida.

The Redlichiida died out before the end of the Middle Cambrian.

Systematics

Nevadia sp. (Family Nevadiidae)
Mesonacis vermontanus (Olenellidae family)
Paradoxides gracilis (family Paradoxididae)
Redlichia (family Redlichiidae)

The order of the Redlichiida is divided into two subordinate orders - Olenellina and Redlichiina - and five superfamilies .

Submission to Olenellina Walcott, 1890

Superfamily Fallotaspidoidea

Familys:

Superfamily Olenelloidea

Familys:

Submission to Redlichiina Harrington, 1959

Superfamily Emuelloidea

Familys:

Superfamily Paradoxidoidea

Familys:

Superfamily Redlichoidea

Familys:

The systematic position of the relatively rare bathynotids has not yet been clarified, but due to the similarities of their shell tops to the Chengkouaspidae they can be made. They had facial sutures and long spikes on the head shield and the last segment of the chest.

The Ellipsocephalidae are occasionally listed as Redlichiida, although they actually belong to the Ptychopariida.

Individual evidence

  1. ^ Richter, R. 1932. Crustacea (paleontology) in: R. Dittler, G. Joos, E. Korschelt, G. Linek, F. Oltmanns, K. Schaum, eds., Concise Dictionary of Natural Sciences, 2nd edition, Verlag Gustav Fischer , Jena, pp. 840-64, fig.A, 1-64. [Order Redlichiida, subordination Redlichiina]
  2. ^ Teiichi Kobayashi : On the Redlichiacea (Trilobita) and the Redlichian Province . In: Proceedings of the Japan Academy , Series B . tape 63 , no. 2 , 1987, pp. 43-46 , doi : 10.2183 / pjab.63.43 ( PDF ).

Web links

Commons : Category “Redlichiida”  - collection of images, videos and audio files

swell

  • Benton, MJ (1993). The Fossil Record 2. Chapman & Hall