NEW EARLY CAMBRIAN BRADORIIDA (CRUSTACEA?) FROM ANTARCTICA: IMPLICATIONS FOR BRADORIID BIOGEOGRAPHY AND EVOLUTION

Bradoriids are small, bivalved stem group crustaceans that comprised an important component of the Cambrian biota, but became extinct during the early Ordovician. Bradoriids have a widespread distribution that roughly mirrors the biogeographic provinces reported for trilobites. Although bradoriids are a common component of the Cambrian biota, this is the first report of bradoriids from Antarctica.

Bradoriids collected from the middle Early Cambrian (Late Atdabanian to Botomian) of the Pensacola Mountains in Antarctica are characterized by a subcircular carapace with a well defined margin, subequal anterior and posterior lobes that are elongated into sharp ridges that extend one third the length of the carapace, and a broad dorsal node occurring along the hinge between the anterior and posterior lobes. The carapace surface exhibits three kinds of ornamentation: fine pitting, pustules, and a network like reticular pattern. Several smaller carapaces with reduced ornamentation collected from the same bed are interpreted as juvenile molt stages.

This new species does not fall within any previously described genera, but is assigned to the family Kunmingellidae and appears to be closely related to Kunmingella from South China. The earliest known bradoriids date from the early Early Cambrian of South China, and Shu and Chen (1994) suggest that later during the Early Cambrian bradoriids dispersed along several independent routes to populate Siberia, Australia, and Laurentia. The proposed relationship of the Antarctic bradoriids to Chinese but not Australian families suggest that a dispersal route may have operated directly from China to Antarctica which bypassed Australia, unlike Shu and Chen’s (1994) reconstruction. The development of a direct dispersal route from South China to Antarctica is also supported by close affinities of some Antarctic trilobites to species or genera found in South China. This new interpretation of bradoriid biogeography and evolutionary pathways may also provide insight into dispersal patterns of other Cambrian clades.