Bradoriids are an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

order of small marine

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s with a bivalved

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

, and were globally distributed, forming a significant portion of the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

and

Early Ordovician 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 million years ago (Mya) to the start of the Silurian Period Mya. ...

soft-bodied communities.

Affinity

Whilst the Bradoriida were traditionally considered as relatives of the modern bivalved arthropod group

Ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

a, the anatomy of their

appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

s does not support such a relationship; neither are they related to the Cambrian bivalved arthropod group

Phosphatocopida Phosphatocopina (alternatively Phosphatocopida) is an extinct group of bivalved arthropods known from the Cambrian period. They are generally sub-milimetric to a few millimetres in size, and are typically found 3-dimensionally preserved in Orste ...

. Rather, they are most probably related to the Eucrustacea at a

stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

level. An in-depth phylogenetic analysis of

Panarthropoda Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada (water bears) and Onychophora (velvet worms). Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphylet ...

included two bradoriid genera, '' Kunyangella'' and ''

Kunmingella ''Kunmingella'' is genus of Cambrian bradoriid from the Chengjiang biota, containing the single species ''K. douvillei''. See also * Arthropod * Cambrian explosion * Chengjiang biota ** List of Chengjiang Biota species by phylum This is a l ...

'', and recovered them as the most basal stem- mandibulates.

Occurrence

Bradoriida are geographically widespread, and first occur in the

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

shortly before the earliest

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

fossils. 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 palaeoequator. Bradoriid diversity was highest along the coasts of South China and eastern Gondwana (Australia) and was relatively low along the Laurentian coast.

References

{{Taxonbar, from=Q4955096 Prehistoric crustaceans Crustacean orders