A NEW GENUS AND SPECIES OF ?PARTHENOGENIC ANOSTRACAN (CRUSTACEA, BRANCHIOPODA, ?THAMNOCEPHALIDAE) FROM THE CRETACEOUS KOONWARRA FOSSIL BEDS IN AUSTRALIA

The fossil record of anostracan crustaceans is poor, with only six formally described species to date, however they range in occurrence from the Devonian to the recent. The Cretaceous Koonwarra Fossil Beds in Australia contain a new species of anostracan, or fairy shrimp, described here. These fossil beds are known for their exceptional faunas of fish and insects from a freshwater lake environment. Previously, the anostracan specimens from Koonwarra were described in open nomenclature as an indeterminate anostracan. This newly described fairy shrimp species is notable for the fact that all the specimens are either females or juveniles (approx. 40 specimens)—no males are known. This suggests that the species may have a parthenogenic mode of reproduction. The species is tentatively assigned to the family Thamnocephalidae, based in part, on the similarity of egg shape in gravid females. The preservation of the fossils matches the results of previous decay experiments on anostracans, showing evidence of decay-induced fabrics despite exceptional preservation of cuticle, digestive tract and internal anatomy to varying degrees.