Treptichnus pedum (formerly Phycodes pedum, Manykodes pedum by J. Dzik, or sometimes wrongly named Trichophycus pedum) is regarded as the earliest widespread complex trace fossil. Its earliest appearance, which was contemporaneous with the last of the Ediacaran biota, is used to define the dividing line between the Ediacaran and Cambrian Periods.
Treptichnus pedum has a fairly complicated and distinctive burrow pattern: along a central, sometimes sinuous or looping burrow it made successive probes upward through the sediment in search of nutrients, generating a trace pattern reminiscent of a fan or twisted rope. The organism that left such traces is considered more complex than earlier Ediacaran fauna; and these trace fossils, which occur worldwide, are usually found in strata above those.
Since only its burrows have been found, it is presumed that the Treptichnus animal lacked any hard anatomical features, such as shells or bones. Its morphology and relationship to modern animals is therefore unknown, and some dispute even its inclusion within the animal kingdom. Despite this lack of fossil evidence, burrows produced by modern priapulid worms are almost identical to Treptichnus, suggesting a close anatomical relationship between the trace-maker and modern priapulids.
The name Treptichnus pedum means "turned-trail (Greek) of feet (Latin)".