(paleontology) A type of fossil reflecting the reworking of sediments and hard substrates by organisms, rather than the physical remains of the organism itself. This includes structures such as burrows, trails, impressions, coprolites and borings.

(evolutionary theory) Any species discovered first as a fossil and believed extinct, but which is later found living; an organism that has remained unchanged over geological periods.

plural of trace fossil

A fossil formed when sediment fills the inside or covers the outside of a dead organism and the organism's remains do not persist, leaving just the shape and texture of the rock to indicate the organic material that was there.

plural of mold fossil

Water that has remained in an aquifer for a long timespan, usually thousands or millions of years.

crude oil

plural of index fossil

(linguistics) A word that is broadly obsolete but remains in current use because it is contained within an idiom that is still in use.

plural of fossil word