trace fossil (ichnofossil) A biogenic sedimentary structure formed by the behavioural activity of an animal on or within a given substrate. The study of trace fossils is called ‘ichnology’. Traces are most frequent at the interface between different lithologies (e.g. sandstone and shale), and are classified on various criteria including morphology and preservation. Of these two, the second is preferred as a toponomic classification (i.e. classification by place of occurrence) and, apart from the processes of preservation, considers the position of the trace within the depositional unit concerned. In 1970, A. Martinsson divided traces into four groups dependent on their relationship to the casting medium: epichnia are surface ridges or grooves; endichnia are tubes or burrows formed within the casting medium; hypichnia are grooves or ridges preserved on the lower surface of the main body of the casting medium; and exichnia are formed by bioturbation outside the main body of the casting medium. See FOSSILIZATION.

trace fossil(ichnofossil) A structure formed in a sediment by the action of a living organism (e.g. a tube, burrow, footprint, or groove made by crawling over a surface) and preserved when the sediment becomes a sedimentary rock. Traces are most commonly found at interfaces between different rock types (e.g. between sandstone and shale) and are classified in various ways, including their forms and the places of their occurrence. See also fossilization.

climax trace fossil A trace fossil produced by a member of a climax community.

trace fossil See fossil.