A trail is an impression made on a surface by the body of a limbless animal. Common usage of the term "trail" implies that it is a synonym of "trackway" or that a well-worn path in a terrestrial ecosystem is a trail (as in a "game trail," made by game animals). Although these colloquial meanings are understandable to most people, the distinction between the method of locomotion by a limbed versus a limbless animal is an important one, hence the distinction made here. The surficial aspect of a trail is also distinctive from a burrow, which represents an excavation into a sediment, rather than the displacement or compaction of sedimentary grains on a surface.
A trail does not necessarily have to form on an exposed surface; some trails follow horizontal bedding planes within a sedimentary pile, hence these are called intrastratal trails. Trails that formed on an exposed surface are called epistratal trails.
Examples of invertebrate animals that leave trails include many gastropods and worms; vertebrates include fish and snakes. Trail formation as a mode of behavior (whether used for feeding or locomotion, combined through grazing) has been represented by metazoans for at least 1.2 billion years, as shown by recently described trace fossils in Precambrian rocks of Texas, USA..
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