Bradoriida

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Bradoriida
Temporal range: Cambrian stage 3–Mid Ordovician[1]
Stereographic pair of a 3D scan of Indiana sp. from the Maotianshan Shales
Life restoration of Kunmingella
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Order: Bradoriida
Raymond, 1935
Families and genera
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Bradoriida, also called bradoriids, are an

Early Ordovician soft-bodied communities.[1] [2]

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

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]

References