Classifications: The Utopia of Classifying the Unclassifiable

Abstract

Traditional classifications of ichnology, based on marine and lacustrine trace fossils, were not prepared to include insect trace fossils, which since the 90s have been producing a deep exercise of thinking and changes in these classifications. Many insect trace fossils, such as cocoons, ovipositions, caddisfly cases, galls, subaerial nests, fall in the grey area of “other evidence of activity” in current classifications or even some of them are questioned as true trace fossils. Insect trace fossils in plant remains are included in the category of bioerosion. The distinction among compound and composite trace fossils is challenged by many insect trace fossils, which are here in a new category: coproduced trace fossils. Larva and adult of the same species of insect may be considered a single producer or two different producers? As an exercise, the ethological classification and categories is reviewed taken in account the selection of substrate as the first order ethological trait to be considered. Different aspects of ichnotaxonomy as the most significant and sound ichnological classification are reviewed. The convenience of creating ichnofamilies is stressed and the already recognized ones are briefly reviewed. Some problems related to trace fossil ichnotaxonomical identification, such as preservational biases, size, distortion with age, are analyzed.