BIOTA AS A MAJOR SOIL-FORMING FACTOR AND ECOSYSTEM ENGINEERS THROUGH RECENT EARTH HISTORY BASED ON CONTINENTAL TRACE FOSSILS—SOIL BIOTA AS GEOENGINEERS

The role of above- and belowground biota as a soil-forming factor, with the exception of plants, has been overlooked and underestimated despite the work of Darwin on worms and vegetable mould, and later studies by Schaller, Thorp, Hole, and Johnson on the work of animals, soil-mixing rates, and biomantles. Only recently is bioturbation by animals as a major soil-forming factor being recognized through pedogenic and geologic studies of soils and paleosols, respectively. Also recently recognized is the work of a variety of animals as allogenic or autogenic ecosystem engineers that directly or indirectly modulate the availability of resources to other species via physical state changes in abiotic or biotic materials through their own physical structures (autogenic) and by transforming materials from one state to another (allogenic). Earthworms, termites, ants, crayfish, a variety of soil bugs and beetles, and a variety of small but abundant burrowing mammals are ecosystem engineers as their burrowing activity (1) changes the physical, chemical, and biological properties of sediment; (2) improves drainage, gas exchange, and oxygenation of soils, and (3) increases microbial activity and decomposition rates. The study of continental trace fossils (neoichnology and paleoichnology) and of paleosols has provided abundant evidence and data that demonstrates the significance of bioturbation in the formation of modern soils, but also in paleosols as early as the Devonian. Traces in mid to late Paleozoic paleosols show synchronicity in their formation. An abundance of trace fossils interpreted as nests and burrows of termites, ants, crayfishs, soil bugs, beetles, and tetrapods (mammals and therapsids) are found in a variety of imperfectly drained to well-drained, immature to mature paleosols. Ichnopedologic fabrics in paleosols produced by representatives of these animals demonstrate that their behaviors have changed little since the early to mid Mesozoic. As these organisms and their activity are paramount today in maintaining ecosystem health through the detritivore nutrient cycling system, sediment mixing, and the creation and destruction of soil features, they should be referred to as geoengineers because they have shaped the evolution of terrestrial ecosystems and continental landscapes since the Mesozoic.