Trichophycus pedum

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Trichophycus pedum (or Treptichnus pedum; formerly Phycodes pedum) is regarded as the earliest wide-spread 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.<ref>Subcommission on Neoproterozoic Stratigraphy - URL retrieved November 27, 2006</ref> Trichophycus produced a fairly complicated and distinctive burrow pattern: along with 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.<ref>McMenamin, Mark A., Dianna L. McMenamin [1990-01-15]. The Emergence of Animals. Columbia University Press. ISBN 0-231-06647-3.</ref> It is considered more complex than earlier Ediacaran fauna; and its trace fossils, which occur worldwide, are usually found in strata above them.<ref>Life in the Cambrian. Retrieved on 2006-03-09.</ref>

Since it lacked any hard anatomical features, such as shells or bones, no fossilized remains of Trichophycus (besides its burrows) have been found. Its morphology and relationship to modern animals is therefore unknown, and some dispute even its inclusion into the animal kingdom.<ref>Altermann, Wladyslaw [2002-07-01]. Precambrian Sedimentary Environments. Blackwell Publishing. ISBN 0-632-06415-3.</ref>