Bradoriida

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Bradoriida
Temporal range: Cambrian stage 3–Mid Ordovician [1]
Indiana Bradoriida.jpg
Stereographic pair of a 3D scan of Indiana sp. from the Maotianshan Shales
Kunmingella.png
Life restoration of Kunmingella
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Order: Bradoriida
Raymond, 1935
Families and genera
and others...

Bradoriida, also called bradoriids, are an extinct order of small marine arthropods with a bivalved carapace, which globally distributed, forming a significant portion of the Cambrian and Early Ordovician soft-bodied communities. [1] [2]

Contents

Affinity

Whilst the Bradoriida were traditionally considered as relatives of the modern bivalved arthropod group Ostracoda, the anatomy of their appendages does not support such a relationship; neither are they related to the Cambrian bivalved arthropod group Phosphatocopina. [1] They have been alternatively recovered as stem-group crustaceans, as stem-group mandibulates, or stem-group arthropods, depending on the analysis. [3]

Description

Most bradoriids are only known from their bivalved carapaces, which are small in size, typically up to around 5 millimetres (316 in) in length. Preserved soft tissues known from some members, such as Kunmingella, Kunyangella and Indiana suggest that the group was morphologically diverse. Indiana had a pair of antennae followed by 11 pairs of uniramous appendages which were all similar to each other. Kunmingella had 12 appendages, including a pair of antennae as well pairs of biramous limbs, including four anterior pairs of appendages bearing double rows of endites on their endopods, and a posterior 5 with only a single row of endites, as well as two terminal pairs of uniramous limbs. Kunyangella has 4 pairs of appendages on the head each with a distinct morphology, with 9 pairs of trunk appendages, the last being uniramous. [3] In Kunmingella, eggs have been found preserved attached to the posteriormost three pairs of biramous limbs, suggesting it engaged in brood care. Around 50–80 eggs, each around 150–180 μm across were attached in total. [4]

Ecology

Bradoriids are thought to have lived either crawling on the seafloor (epibenthic) or swimming close to the seafloor (nektobenthic). [3] Bradoriids are proposed to have been detritus feeders, scavengers, or micro predators of soft-bodied prey. [5]

Occurrence

Bradoriida are geographically widespread, and first occur in the fossil record shortly before the earliest trilobite fossils. [1] Their taxonomic composition broadly reflects two geographical provinces ("European" and "4A", i.e. America, Asia, Australia, Antarctica) which approximately mirror trilobite provinces, with the 4A area representing warmer waters closer to the palaeo equator. [1] Bradoriid diversity was highest along the coasts of South China and eastern Gondwana (Australia) and was relatively low along the Laurentian coast. [5] Bradoriids severely declined in abundance from the late Middle Cambrian onwards, with only a handful of genera continuing into the Late Cambrian and Early Ordovician. [5]

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<i>Pygmaclypeatus</i> Extinct genus of arthropod

Pygmaclypeatus is a genus of trilobite-like arthropod from the Cambrian aged Chengjiang biota of southern China. The carapace is flat and broad, and slightly shorter than it is wide, reaching a maximum width of 17.5 millimetres (0.69 in) and length of 14 millimetres (0.55 in). The headshield makes up about 25% of the total length, and has attached a pair of antennae, as well as four pairs of biramous limbs. The trunk has 6 tergites, each associated with a pair of biramous limbs along with a terminal pygidium associated with four pairs of biramous appendages and a segmented short tailspine. The well developed paddle-like exopodites on the trunk and pygidium limbs along with its small size suggests that it was an effective swimmer with a strong power stroke, and that it probably had a nektobenthic mode of life, swimming close to the ocean floor. Given its delicate spinose endites on the limbs it likely only consumed soft food and organic particles. It is considered to be closely related to Retifacies from the same deposit with shared characters including a segmented tailspine. It has been placed as a member of Artiopoda, possibly along with Retifacies the earliest diverging lineage of the Trilobitomorpha.

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Isoxyids are members of the order Isoxyida and the family Isoxyidae, a group of basal arthropods that existed during the Cambrian period. It contains two genera, Isoxys, with 20 species found worldwide, and Surusicaris known from a single species found in the Burgess Shale of Canada. They are distinguished by their bivalved carapaces and pair of upward curving grasping frontal appendages.

References

  1. 1 2 3 4 5 Timothy P. Topper; Christian B. Skovsted; Glenn A. Brock & John R. Paterson (2011). "The oldest bivalved arthropods from the early Cambrian of East Gondwana: systematics, biostratigraphy and biogeography". Gondwana Research. 19 (1): 310–326. Bibcode:2011GondR..19..310T. doi:10.1016/j.gr.2010.05.012.
  2. Mark A. S. McMenamin (2020). "Bradoriids (Arthropoda) and the Cambrian Diversification". Geosciences. 10 (4): 119. Bibcode:2020Geosc..10..119M. doi: 10.3390/geosciences10040119 .
  3. 1 2 3 Zhai, Dayou; Williams, Mark; Siveter, David J.; Harvey, Thomas H. P.; Sansom, Robert S.; Gabbott, Sarah E.; Siveter, Derek J.; Ma, Xiaoya; Zhou, Runqing; Liu, Yu; Hou, Xianguang (2019-09-03). "Variation in appendages in early Cambrian bradoriids reveals a wide range of body plans in stem-euarthropods". Communications Biology. 2 (1): 329. doi:10.1038/s42003-019-0573-5. ISSN   2399-3642. PMC   6722085 . PMID   31508504.
  4. Duan, Yanhong; Han, Jian; Fu, Dongjing; Zhang, Xingliang; Yang, Xiaoguang; Komiya, Tsuyoshi; Shu, Degan (April 2014). "Reproductive strategy of the bradoriid arthropod Kunmingella douvillei from the Lower Cambrian Chengjiang Lagerstätte, South China". Gondwana Research. 25 (3): 983–990. Bibcode:2014GondR..25..983D. doi:10.1016/j.gr.2013.03.011.
  5. 1 2 3 Williams, Mark; Siveter, David J.; Popov, Leonid E.; Vannier, Jean M. C. (14 May 2007). "Biogeography and affinities of the bradoriid arthropods: Cosmopolitan microbenthos of the Cambrian seas". Palaeogeography, Palaeoclimatology, Palaeoecology . 248 (1–2): 202–232. Bibcode:2007PPP...248..202W. doi:10.1016/j.palaeo.2006.12.004 . Retrieved 14 November 2022.