“TRACES” OF HIDDEN BIODIVERSITY IN PALEOSOLS: EXAMPLES FROM PHANEROZOIC TERRESTRIAL DEPOSITS

Terrestrial soil ecosystems, in existence since the Early Proterozoic, have changed through time with the evolution, diversification, and extinction of microbes, fungi, plants, animals, and the biotopes they formed. Ichnofossils and paleosols are the result of organism-substrate and organism-organism interactions that represent the “hidden” biodiversity of feeding, burrowing, nesting, reproducing, and rooting transient to permanent soil biota. The term “hidden” signifies biodiversity that is not recorded by body fossils for that region or time, and thus, not identified as a component of the ecosystem. Ichnofossils are the best in-situ evidence of biotic components in paleosol ecosystems.

Mid- to late Paleozoic to Recent soils contain suites of ichnofossils reflecting the coevolution of vegetation, invertebrates, vertebrates, and the detritivore-dominated nutrient cycle in soil ecosystems. Trace fossils of macrofauna and rooting plants (and other odd autotrophs and saprotrophs) in paleosols reflect the presence of micro- and meso-faunal and -floral elements of ancient ecosystems that are not preserved or are too small to be recognized. Many of the macrofaunal elements likely represent the behavior of ecosystem engineers because they directly or indirectly modulated the resource availability for other biota in paleosol ecosystems. The nature and extent to which organism behavior change or control the abiotic or biotic character of the paleoenvironment determine if the traces represent ecosystem engineering.

In most of these paleosols, the ichnofossil diversity and abundance reflect the primary productivity (PP), the intensity of pedogenesis, and the overall climatic setting. Paleoecosystems with low PP have few or no ichnofossils, whereas paleoecosystems with medium to high PP have high ichnofossil diversity and abundance, but exhibit low ichnofossil diversity in areas of very high PP due to intense leaching from high rainfall and temperature.

Examples of hidden biodiversity in paleosols from the Ordovician, Devonian, Triassic, Jurassic, and Eocene outnumber the body fossils within these deposits. In-depth studies of ancient ecosystems, combined with modern analog studies, will add to our knowledge of the evolution of terrestrial soil ecosystems.