A new genus and species of ?parthenogenic anostracan (Pancrustacea, Branchiopoda, ?Thamnocephalidae) from the Lower Cretaceous Koonwarra Fossil Bed in Australia

Abstract

The fossil record of fairy shrimp, or anostracan crustaceans, is poor with only six species formally described to date. The group stratigraphically ranges from the Devonian to recent. The Lower Cretaceous (middle–upper Aptian) Koonwarra Fossil Bed in Australia contains a new species of anostracan, which we describe here. The Koonwarra Fossil Bed is famous for its rich fossil assemblage of avian-line dinosaur feathers, bony fish, insects and aquatic invertebrates that were preserved in the fine bottom sediments of a restricted montane waterbody. Previously, the Koonwarra Fossil Bed anostracans were classified as taxonomically indeterminate; however, we show that they are potentially attributable to Thamnocephalidae based on the egg shape found in gravid female individuals. Notably, all of the recovered Koonwarra Fossil Bed anostracans (∼40 individuals) are either females or juveniles. This suggests that the species might have undergone parthenogenic reproduction. Furthermore, the preservation of the fossils resembles experimentally decayed modern anostracans, evidencing decay-induced fabrics that retained remnants of the cuticle, digestive tract and internal anatomy to varying degrees. Emma Van Houte [vanh1629@fredonia.edu], Department of Geology and Environmental Sciences, SUNY Fredonia, Fredonia, NY 14063, USA; Thomas A. Hegna [thomas.hegna@fredonia.edu], Department of Geology and Environmental Sciences, SUNY Fredonia, Fredonia, NY 14063, USA; Aodhán D. Butler [aodhan.b@gmail.com], Palaeobiology Programme, Department of Earth Sciences: Uppsala University, Villavägen 16, Uppsala 75236, Sweden.