(formerly named Treptichnus , Phycodes by Manykodes J. Dzik, and also known as  Trichophycus ) is the preserved burrow of an animal. As such, it is regarded as the earliest widespread complex  trace fossil. Its earliest appearance, around 542 mya, which was contemporaneous with the last of the  Ediacaran biota, is used to help define the dividing line, considered geologically at 541 mya, between the Ediacaran and Cambrian periods.  It is last seen in the fossil record during the  Cenomanian (99.7 Ma).
^ a b AK Rindsberg and DC Kopaska-Merkel. 2005. Treptichnus and Arenicolites from the Steven C. Minkin Paleozoic Footprint Site (Langsettian, Alabama, USA). Alabama Paleontological Society Monograph 1 : 121-141
^ a b
DZIK, Jerzy (2005). "Behavioral and anatomical unity of the earliest burrowing animals and the cause of the "Cambrian explosion" " (PDF). Paleobiology. 31 (3): 503–521. doi: 10.1666/0094-8373(2005)031[0503:BAAUOT]2.0.CO;2.
^ a b See e.g.
fossiilid.info: paleodiversity in Baltoscandia: Trichophycus pedum
Srivastava, Purnima (June 2012). "Treptichnus pedum: An Ichnofossil Representing Ediacaran - Cambrian Boundary in the Nagaur Group, the Marwar Supergroup, Rajasthan, India" (PDF). Proc. Indian Natl. Sci. Acad. 78 (2): 161–169 . Retrieved . April 8, 2016
Subcommission on Neoproterozoic Stratigraphy - URL retrieved June 22, 2009
^ International Commission on Stratigraphy, International Chronostratigraphic Chart, 2012,