2.2. Model organisms.
We used nauplii L1 and L2 of Artemia salina (Branchiopoda, Crustacea) for the burial experiments. This model organism is suitable for our purposes because small crustacean fossils are found in many Lagerstätten, and also because its bright orange coloration helps to find the carcasses in the sediment. The nauplii were obtained from eggs after 36-48 hours of incubation and killed by keeping in fresh water for 4-6 hours.
For the experiments with the deposition of aluminium, we used unicellular and primitive multicellular model organisms: freshwater sponge Spongilla lacustris (Demospongiae, Porifera), flagellateEuglena gracilis (Euglenozoa, Excavata) and social amoebaDictyostelium discoideum (Amoebozoa). S. lacustris was collected in summer 2018 from Moskva river (Zvenigorodskaya biological station, Russia) and kept as a cryopreserved viable specimen. E. gracilis was cultured at the Faculty of Biology, Moscow State University, on the Kramer-Mayer medium (1 g/L (NH4)2HPO4, 1 g/L KH2PO4, 0.8 g/L Na2C6H5O7×5H2O, 0.2 g/L MgSO4, 0.02 g/L CaCl2, 3 mg/L Fe2(SO4)3×H2O, 1.8 mg/L MnCl2×4H2O, 1.3 mg/L CoCl2×6H2O, 0.4 mg/L ZnSO4×7H2O, 0.2 mg/L Na3Mo4×2H2O, 0.02 mg/L CuSO4×5H2O, 20 μg/L thiamine, 10 μg/L cobalamine, etanol to 0.2M; pH 6.6-6.7). D. discoideum strain DBS0237637 from Dicty Stock Center (Northwestern University, Chicago, IL, USA) was grown on E.coli lawn on agar plates with SM5 medium (2 g/L glucose, 2 g/L Bacto Peptone (Oxoid), 2 g/L yeast extract (Oxoid), 0.2 g/L MgCl2, 1.9 g/L KHPO4, 1 g/L K2HPO4,15 g/L agar). Before the experiments, Spongilla and Euglena were killed by freezing in liquid nitrogen, and D. discoideum by keeping in 500 µM/L sodium azide for 15 minutes (Sadiq, 1995).