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Keywords:

  • Classification;
  • Metazoan Evolution;
  • Phanerozoic;
  • Proterozoic;
  • Topological Analysis;
  • Trace Fossils

Topological fidelity of metazoan traces formed by metazoan behaviour is little influenced by compaction, diagenesis, continuous soft-sediment deformation and biostratinomy, substrate consistency, etc., whereas all of these can greatly alter the Euclidean geometric attributes of metazoan traces. Morphological characteristics of trace fossils can be distinguished and described objectively by both topological and Euclidean geometric parameters. The former constitute the basis of ichnoorder and ichnofamily. On the basis of topological criteria, metazoan traces can be classified as 4 ichnoorders and 22 ichnofamilies, consisting of 9 basic and 3 combined topological configurations. At a topological level, the behavioural diversity and complexity indicated by metazoan topoichnotaxa remain fairly stable in the Phanerozoic. All ichnoorders, 75% of ichnofamilies and all 9 basic topological configurations of metazoan traces are formed in the late Neoproterozoic, and all ichnofamilies, a combination of topological configurations and the most complex and highest level of topological configurations of metazoan traces, occurred in the early Cambrian. The evolution of metazoan traces can be expressed in three ranks. Changes at ichnoorder level constitute the first evolution, which is associated with the advent of kingdoms (animalia and plantae, etc.) and phyla (Ediacara and bilaterian, etc.), and the first level of palaeoecological and palaeoenvironmental changes, such as the appearance or disappearance of an ecosystem (Precambrian biomat). The first evolution terminated in the late Neoproterozoic. Changes at the ichnofamily level constitute the second evolution, which is associated with the advent of important phyla such as coelomate animal explosion and the second level of palaeoecological and palaeoenvironmental changes, such as structural changes within an ecosystem. The second evolution terminated in the early Cambrian. Changes at the ichnogeneric and ichnospecific levels constitute the third evolution, which is associated with the appearance or disappearance of the organic taxa lower than phylum, such as dinosaurs and birds, etc., and the third and fourth levels of palaeoecological and palaeoenvironmental changes, such as community-type level changes, within an established ecological structure and community level. The third evolution has been taking place since the Proterozoic.