Marrellomorpha are an extinct group of arthropods known from the Cambrian to the Early Devonian.[1] They lacked mineralised hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution. The best known member is Marrella, with thousands of specimens found in the Cambrian aged Burgess Shale of Canada.

Taxonomy

The group is divided up into two major orders, Marrellida and Acercostraca. Marrellida is recognised by the possession of head shields with two or three pairs of elongate spine-like projections, and three attached pairs of uniramous (single-branched) appendages, while Acercostraca generally have large ovoid carapaces that cover the entire upper half of the body, and five pairs of uniramous appendages attached to the head section. Both groups have unbranched antennae and a segmented trunk with biramous (divided into two branches) appendages.[2] Recent research has suggested the previously enigmatic Cambrian trilobite-like arthropods Skania and Primicaris belong to this group.[3][2] Their phylogenetic position is uncertain, various studies have alternatively placed them in the Arachnomorpha as relatives of Artiopoda (trilobites and kin), as related to Mandibulata (the group containing crustaceans, insects and myriapods), or as stem group euarthropods.[2] The engimatic Cambrian arthropod Burgessia may be closely related to marrellomorphs.[4] Some authors have proposed that they may be closely related to sea spiders (Pycnogonida) within Chelicerata though the cladistical support for such a relationship is relatively weak.[2]

Internal taxonomy of Marrellomorpha after Moysiuk et al., 2022.[2]

Fragmentary taxa assigned to Marrellomorpha include Austromarrella from Cambrian Series 3 aged deposits in Australia,[5] and Dyrnwynia from the Ordovician (Darriwilian) aged Llanfallteg Formation of Wales, which in its original description was assigned to Marrelida.[6]

Phylogeny

After Legg, 2016.[7]

Outgroups

Marrellomorpha
Marrellida

Marrella splendens

Mimetasteridae
Acercostraca

After Moysiuk et al., 2022.[2]

Taxa usually not
considered marrellomorphs

References

  1. ^ Rak, Štĕpán; Ortega-Hernández, Javier; Legg, David A. (2011). "A revision of the Late Ordovician marrellomorph arthropod Furca bohemica from Czech Republic". Acta Palaeontologica Polonica. doi:10.4202/app.2011.0038.
  2. ^ a b c d e f Moysiuk, Joseph; Izquierdo-López, Alejandro; Kampouris, George E.; Caron, Jean-Bernard (July 2022). "A new marrellomorph arthropod from southern Ontario: a rare case of soft-tissue preservation on a Late Ordovician open marine shelf". Journal of Paleontology. 96 (4): 859–874. Bibcode:2022JPal...96..859M. doi:10.1017/jpa.2022.11. ISSN 0022-3360.
  3. ^ Legg, D.A. (2015-09-30). "The morphology and affinities of Skania fragilis (Arthropoda) from the middle Cambrian Burgess Shale". Bulletin of Geosciences: 509–518. doi:10.3140/bull.geosci.1532. ISSN 1802-8225.
  4. ^ Ortega-Hernández, Javier; Legg, David A.; Braddy, Simon J. (February 2013). "The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda". Cladistics. 29 (1): 15–45. doi:10.1111/j.1096-0031.2012.00413.x. ISSN 0748-3007. PMID 34814371.
  5. ^ Haug, Joachim T.; Castellani, Christopher; Haug, Carolin; Waloszek, Dieter; Maas, Andreas (2012). "A Marrella-like arthropod from the Cambrian of Australia: A new link between "Orsten"-type and Burgess Shale assemblages". Acta Palaeontologica Polonica. 58 (3): 629–639. doi:10.4202/app.2011.0120.
  6. ^ Legg, David (2016). "A new marrellid arthropod from the Ordovician of Wales". Acta Palaeontologica Polonica. 61. doi:10.4202/app.00246.2016. ISSN 0567-7920.
  7. ^ Legg, David A. (2016-02-27). "An acercostracan marrellomorph (Euarthropoda) from the Lower Ordovician of Morocco". The Science of Nature. 103 (3): 21. Bibcode:2016SciNa.103...21L. doi:10.1007/s00114-016-1352-5. ISSN 1432-1904. PMID 26922777.


Allikas: https://en.wikipedia.org/wiki/Marrellomorph
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