Mitrate

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Mitrate
Temporal range: Cambrian–Carboniferous (Guzhangian–Morrowan) [1]
Rhenocystis latipedunculata.png
Rhenocystis latipedunculata ventral/flat (B1) and dorsal/convex (B2) surfaces
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Echinodermata
Class:† Stylophora
Order:† Mitrata
Jaekel, 1918
Taxa

See Taxa

Mitrates are an extinct group of echinoderms, which are grouped with the cornutes and the basal Ceratocystis to form the Stylophora. Mitrates were central to the now-disproven [2] calcichordate hypothesis of chordate origins, but are now seen as either pre-radial-symmetry stem-group echinoderms, [3] or as a derived group either within the blastozoans [4] or near to the origin of crinoids. [5]

Contents

Morphology

The organisms were a few millimetres long. [6] Like the echinoderms, they are covered in armour plates, each of which comprises a single crystal of calcite. This is one of the features they share with the latter group, along with a water vascular system, only discovered in 2019. [7] However, they do not display the familiar fivefold symmetry that more recent echinoderms possess, instead being close to (but not fully) bilaterally symmetrical. [6] [8]

Their heads had two sides; one, flat, was covered with large "pavement-like" [6] plates, the other, convex, bore smaller plates. [6] Their tails were long and segmented, resembling the stalk of a crinoid or the arm of a brittlestar. [6] At the opposite end was a hole which may have been mouth or anus - or both. [6]

They also bear features reminiscent of pharyngeal slits, [9] a character lost in other echinoderms but present in hemichordates. [6] This caused R.P.S. Jefferies to hold them as the ancestor of all chordates, a theory that has since been disproven. [2]

Behaviour

The mitrate Rhenocystis latipedunculata has been found with associated trace fossils. [10] [11] Their interpretation requires an understanding of how the animal was oriented in life; it's not agreed whether the convex side of the head was up or down, or indeed whether the "tail" was at the front or back of the organism. [6] The trace fossils suggest that they pulled themselves through the mud with their "tail", and were flat-side up. [6]

Taxa

The following taxa are recognized as being included in the order Mitrata: [12]

References

  1. ↑ Mitrata in the Paleobiology Database
  2. 1 2 Boisset, Thomas; Lefebvre, Bertrand; Mooi, Rich; Kroh, Andreas; Winkler, Viola; Adrien, Jérôme; Martin, Markus J. (2024). "Insights into stylophoran anatomy and taphonomy based on an exceptionally preserved mitrate from the Lorraine Group (Upper Ordovician) of New York, USA". Cah. Biol. Mar. 65: 511–516. doi:10.21411/CBM.A.33CFD1AB.
  3. ↑ Rahman, Imran A.; Zamora, Samuel (July 2024). "Origin and early evolution of echinoderms". Annual Review of Earth and Planetary Sciences. 52 (1): 295–320. Bibcode:2024AREPS..52..295R. doi:10.1146/annurev-earth-031621-113343. hdl: 10141/623070 .
  4. ↑ Mooi, Rich; Lefebvre, Bertrand; Guensburg, Thomas E.; Nohejovlá, Martina; Dupichaud, Christophe (December 2024). "Approaches to understanding echinoderm origins. Part 2: Questioning conceptual models". Cahiers de Biologie Marine. 65: 463–490. doi:10.21411/CBM.A.604F2876.
  5. ↑ Guensburg, Thomas E.; Sprinkle, James; Mooi, Rich; Lefebvre, Bertrand; David, Bruno; Roux, Michel; Derstler, Kraig (2020). "Athenacrinus n. gen. and other early echinoderm taxa inform crinoid origin and arm evolution". Journal of Paleontology. 94 (2): 311–333. doi:10.1017/jpa.2019.87.
  6. 1 2 3 4 5 6 7 8 9 Gee, Henry (October 2000). "Mitrates on the move". Nature. 407 (6806): 849–851. doi:10.1038/35038193. ISSN   0028-0836.
  7. ↑ Lefebvre, Bertrand; Guensburg, Thomas E.; Martin, Emmanuel L. O.; Mooi, Rich; Nardin, Elise; Nohejlová, Martina; Saleh, Farid; Kouraïss, Khaoula; El Hariri, Khadija (2019-02-01). "Exceptionally preserved soft parts in fossils from the Lower Ordovician of Morocco clarify stylophoran affinities within basal deuterostomes". Geobios. 52: 27–36. Bibcode:2019Geobi..52...27L. doi: 10.1016/j.geobios.2018.11.001 . ISSN   0016-6995.
  8. ↑ "Palaeos Metazoa: Deuterostomia: Stylophora" . Retrieved 2023-03-04.
  9. ↑ Jefferies, R.P.S. (1986). The Ancestry of the Vertebrates. British Museum (Natural History).
  10. ↑ Sutcliffe, Owen E.; Südkamp, Wouter H.; Jefferies, Richard P. S. (March 2000). "Ichnological evidence on the behaviour of mitrates: two trails associated with the Devonian mitrate Rhenocystis". Lethaia. 33 (1): 1–12. doi:10.1080/00241160050150267. ISSN   0024-1164.
  11. ↑ Rahman, Imran A.; Jefferies, Richard P. S.; SüDkamp, Wouter H.; Smith, Ru D. A. (January 2009). "Ichnological insights into mitrate palaeobiology". Palaeontology. 52 (1): 127–138. doi:10.1111/j.1475-4983.2008.00838.x. ISSN   0031-0239.
  12. ↑ Domínguez Alonso, Patricio; Jefferies, Richard P. S.; Gil Cid, María Dolores (December 2002). "An annotated check-list of genera and species of carpoids". Coloquios de Palcontologia. 53: 33–68. ISSN   1132-1660.
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