WHERE HAS EVERY “BODY” GONE? WHY THE TRACE FOSSIL RECORD OF INSECTS AND OTHER TERRESTRIAL ARTHROPODS IS SOOOOOOO GOOD…

The ichnofossil record of insects and other terrestrial arthropods is surprisingly diverse and abundant. Often continental deposits that are considered unfossiliferous commonly contain trace fossils of terrestrial and freshwater organisms. Terrestrial arthropods constructed the majority of these traces. Such occurrences ultimately demonstrate that the ichnofossils of arthropods are more abundant in occurrence and distribution through the geologic record. Although the earliest occurrence of body fossils are used to delineate the origin of insect species and arthropods, their ichnofossils—when diagnostic, can be used as proxies for body fossils to extend the time of origination and much can be learned from insect and arthropod ichnofossils.

The ichnofossils of insects and other terrestrial arthropods are diverse and abundant because (1) they were preferentially preserved in paleosols of various maturities via pedogenic processes, (2) many were constructed and reinforced rather than merely excavated, and (3) for the most part these insects had “one-foot-in-the-grave”. Arthropods, from temporary to permanent in their life cycles and habitation of the substrate, play a major role in the soil forming process through their burrowing and nesting activities by forming voids, backing-filling, regulating soil moisture, air, and water movement, mounding, and regulating litter. Adults, juveniles, and larvae burrowed and constructed structures to some degree. Terrestrial arthropods lived solitary, gregariously, or socially in colonies that resulted in simple to complex and extensive burrow systems (or nests). The wetting and drying phases of soils mobilized cations and other constituents that were attracted to organics compounds associated with burrows and nests, preferentially preserving them. Here, body fossils have extremely poor preservation potential because soils forming on alluvial deposits (also floodplain ponds, lakes) are mixed and aerated.

Many examples of ichnofossil-bearing paleosols from the Mesozoic and Cenozoic attest to the dominance of arthropods preserved in the geologic record. Interestingly, trace fossils interpreted as arthropod burrows are surprisingly abundant in Mid- and Late Paleozoic deposits and will add to our knowledge of early terrestrial arthropods.