Mongolepidida

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Mongolepidida
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Mongolepidida
Karatajūtė-Talimaa, Novitskaya, Rozman & Sodov, 1990
Families [1]

The Mongolepidida is an order of primitive elasmobranchs that lived during the Late Silurian and Early Devonian periods of Russia and Mongolia, with possible fragmentary remains dating back to the Katian epoch of the Late Ordovician (c.450 Ma). [2] The three known genera are: Elegestolepis , [3] Mongolepis [4] and Polymerolepis . [5] [2] [6] [7] They are only known from fragmentary placoid scales, so their appearance is unknown. The oldest of these scales have been dated back to the Ludlow epoch (427.4 Ma to 423 Ma), making the members of the Mongolepidida possibly the oldest sharks known to date. [8]

Although the placoid scales of the Mongolepidida are accepted to be those of sharks, subtle differences in the scales suggest that they may have been quite different in appearance to modern sharks. It is not known what they looked like due to the fragmentary nature of the known remains. [9]

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Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opercula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.

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The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 Ma to the start of the Silurian Period 443.8 Ma.

The PaleozoicEra is the first of three geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic and ends 251.9 Ma at the start of the Mesozoic Era. The Paleozoic is subdivided into six geologic periods :

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The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.

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Elegestolepis is a primitive shark from the Mongolepidida that lived during the Silurian and Devonian periods in Russia with only one species, E. grossi, known to date. It was closely related to Mongolepis and Polymerolepis. It is only known from fragmentary placoid scales discovered in Russia before 1973. The oldest of these scales have been dated back to the Ludlow epoch, making Elegestolepis the oldest known shark. Elegestolepis dates back to about 420 years ago, but some scales that may yet represent another shark ancestor are known from 450 million years ago.

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Valentina Karatajūtė-Talimaa was a Lithuanian geologist and paleontologist. Best known for her contributions to the world of vertebrate fossils and vertebrate paleontology, She discovered over 100 new species during her career.

<i>Qianodus</i> Extinct Silurian chondrichthyan genus

Qianodus is a jawed vertebrate genus that is based on disarticulated teeth from the lower Silurian of China. The type and only species of Qianodus, Q. duplicis, is known from compound dental elements called tooth whorls, each consisting of multiple tooth generations carried by a spiral-shaped base. The tooth whorls of Qianodus represent the oldest unequivocal remains of a toothed vertebrate, predating previously recorded occurrences by about 14 million years. The specimens attributed to the genus come from limestone conglomerate beds of the Rongxi Formation exposed near the village of Leijiatun, Guizhou Province, China. These horizons have been interpreted as tidal deposits1 that form part of the shallow marine sequences of the Rongxi Formation.

<i>Fanjingshania</i> Extinct genus of cartilaginous fishes

Fanjingshania is an extinct genus of "acanthodian" stem-chondrichthyans from the lower Silurian of China around 439 million years old, making it currently the oldest known acanthodian. It comprises a single species, Fanjingshania renovata which is known from over 1,000 isolated elements, including fin spines, branchiostegal plates, sclerotic plates, trunk scales, and tectal and postorbital tesserae. No teeth were ascribed to the taxon, but in the same horizon the tooth taxon Qianodus was found, and these taxa may be synonymous. In a phylogenetic analysis accompanying the description, it was placed in a clade with Climatius, Parexus, and Ptomacanthus.

References

  1. IRMNG (2023). Mongolepidida †. Accessed at: https://www.irmng.org/aphia.php?p=taxdetails&id=10434 on 5 August 2024
  2. 1 2 Andreev, Plamen; Coates, Michael I.; Karatajūtė-Talimaa, Valentina; Shelton, Richard M.; Cooper, Paul R.; Wang, Nian-Zhong; Sansom, Ivan J. (2016). "The systematics of the Mongolepidida (Chondrichthyes) and the Ordovician origins of the clade". PeerJ. 4: e1850. doi: 10.7717/peerj.1850 . PMC   4918221 . PMID   27350896.
  3. "Elestegolepis". www.planetsharkdivers.com. Archived from the original on 24 October 2020. Retrieved 12 August 2020.
  4. "Mongolepis". www.planetsharkdivers.com.
  5. "Polymerolepis". www.planetsharkdivers.com.
  6. Karatajùtè-Talimaa, Valentina (1 January 1995). "The Mongolepidida: Scale structure and systematic position" . Geobios. Premiers Vertandébrandés et Vertandébrandés Infandérieurs. 28: 35–37. Bibcode:1995Geobi..28...35K. doi:10.1016/S0016-6995(95)80083-2 . Retrieved 14 August 2020.
  7. Andreev, Plamen; Zhao, Wenjin; Wang, Nian-Zhong; Meredith Smith, Moya; Li, Qiang; Cui, Xindong; Zhu, Min; Sansom, Ivan (13 February 2020). "Early Silurian chondrichthyans from the Tarim Basin (Xinjiang, China)". PLOS ONE. 15 (2): e0228589. Bibcode:2020PLoSO..1528589A. doi: 10.1371/journal.pone.0228589 . PMC   7018067 . PMID   32053606.
  8. "The Paleobiology Database". paleobiodb.org. Retrieved 5 May 2016.
  9. "Prehistoric Sharks | Sharkopedia". Archived from the original on 12 July 2018. Retrieved 12 August 2020.