Other Characters: Shape, Fillings and Further Micromorphological Characters

Abstract

Besides the wall, shape and filling are the next most important characters to define trace fossils. Regarding the shape, enlargement of burrows or chambers, known with different terms according to their function and insect taxa considered, is the most distinctive character of insect trace fossils in paleosols. The function of these chambers produced by insects is mostly nesting or pupating, and also feeding or aestivating. Problems in ichnotaxonomy of insect trace fossils resulting from the simple shapes of some insect chambers are depicted. Different criteria to distinguish between inorganic structures, such as concretions, and true trace fossils and also for distinguishing among different insect ichnotaxa based on shape are reviewed. Different shapes and the connection of chambers to burrows are illustrated. Techniques utilized and reviewed in this chapter to study shape are micromorphology, SEM images, casts, CT images, X-ray radiography, 3D software, MRI and MLT. Insect trace fossils in paleosols may show passive, meniscate fillings of different origins, and pelletal ones. They may show also root nets. Micromorphological characters present indistinctly in walls and fillings are phytoliths, which allow for inferences on dung beetle behavior, paleoenvironments and dung providers diets. It is reviewed the micromorphological evidence of termite activity in laterites, such as presence of pellets, bands of fecal origin, clay microaggregates, plant remains, termite cuticle and intestinal flagellates.