The microanatomical and histological structure of different-sized femurs and hypocentra of the archegosauroid amphibian Platyoposaurus stuckenbergi from the Middle Permian (Urzhum horizon, Estemmenosuchus uralensis zone) of Eastern Europe is described, a comparative characteristic of age variability is given, and ecological features of the species are also considered. P. stuckenbergi femurs are characterized by the complete absence of calcified cartilage and the presence of up to 15 lines of arrested growth (LAG’s); hypocentra - osteoporotic structure, lack of calcified cartilage and LAG’s. Microanatomical and morphological features indicate the predominantly aquatic lifestyle of Platyoposaurus as an active predator of river and lake habitats.