Baissa is a lower Cretaceous locality in Siberia, on the left bank of the Vitim River. The Zaza Formation sediments exposed at Baissa are represented mostly by sandstones, siltstones, marls and bituminous shales. The total thickness if the section is about 80 m. Insect remains occur throughout the section, except for the most coarse-grained rocks. Their abundance and state of preservation vary from one bed to another.
Baissa is the only locality in the World where 24 pterygote insect orders are found. These are Ephemeroptera, Odonata, Grylloblattodea, Plecoptera, Blattodea, Mantodea, Isoptera, Dermaptera, Orthoptera, Phasmatodea, Psocoptera, Phthiraptera, Thysanoptera, Hemiptera, Megaloptera, Raphidioptera, Neuroptera, Coleoptera, Mecoptera, Siphonaptera, Trichoptera, Diptera, Lepidoptera, and Hymenoptera, comprising in total about 195 families.
Excellently preserved spiders, conchostracans, ostracods, gastropods, pelecypods, fresh-water bryozoans, fishes, bird feathers, and diverse plant remains are also known from this site. Several species of insect trace fossils have been recorded as well.
- Zherikhin, V.V., Mostovski, M.B., Vrsansky, P., Blagoderov, V.A. and Lukashevich, E.D. 1999. The unique Lower Cretaceous locality of Baissa and other contemporaneous insect-bearing sites in North and West Transbaikalia. Proceedings of the First Palaeoentomological Conference, Moscow, 1998. Bratislava: Amba Projects, pp. 185-192.