Insect J3-K1 assemblage from Tasgorosay in Kazakhstan was dominated by cockroaches

The understudied locality of Tasgorosay tract, Karzhantau ridge in Kazakhstan offers an interesting, yet very homologous array of fossil insects. The material used for this research was comprised nearly solely of the cockroaches Caloblattina hrachova Majtaník and Praeblattela solus Majtaník, spp. n. ( n = 15, 2, respectively), with the former being seemingly much more common. Tasgorosailus orlovskajae Gorokhov, 1990 was also present ( n = 2). Phylogenetical relation of these two species suggests a Lower Cretaceous age of the sedimentary rocks containers. The near absence of insects other than Blattaria might result from the taphonomic situation of predepositional transport and duration of pre-burial in the waterbody. Organic matter in the sediment suggests that cockroaches lived at the edge of a wetland located near a freshwater lake. The stagnant regime of the lake, high algal primary productivity, and the supply of terrestrial vegetation resulted in the formation of an anoxic regime at the bottom, where the deposited organic matter was decomposed by anaerobic bacteria. Wildfires of coastal wetland vegetation and especially the gases escaping from the smouldering swamp could have negatively affected the cockroaches' behavior, which ultimately could have contributed to their standard mortality. Burying into fine sediments resulted in detailed wing impressions. Slow anaerobic microbial decomposition led to the removal of bodies and then also chitin from the exoskeleton of fossilising cockroaches.