''Treptichnus'' (formerly named ''Phycodes'', ''Manykodes'' by J. Dzik, and also known as ''Trichophycus''See e.g
fossiilid.info: paleodiversity in Baltoscandia: Trichophycus pedum
/ref>) is the preserved burrow of an animal. As such, it is regarded as the earliest widespread complex

trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

. Its earliest appearance, around 542 mya, which was contemporaneous with the last of the

Ediacaran biota The Ediacaran (; formerly Vendian) biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were composed of enigmatic tubular and frond-shaped, mostly sess ...

, is used to help define the dividing line, considered geologically at 541 mya, between the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and t ...

and

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

periods. It is last seen in the fossil record during the

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in ...

(99.7 Ma).

Description

''Treptichnus pedum'' has a fairly complicated and distinctive

burrow An Eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of s ...

pattern: along a central, sometimes sinuous or looping burrow it made successive probes upward through the

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

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

; and these

s, which occur worldwide, are usually found in

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

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

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s. 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, surface trails produced by modern priapulid worms exhibit the same probing morphology as ''Treptichnus'', suggesting a close anatomical relationship between the trace-maker and modern priapulids.

Etymology

The name ''Treptichnus pedum'' means "turned-trail (Greek) of feet (Latin)".

References

Cambrian life Burrow fossils Index fossils {{trace-fossil-stub