Treptichnus pedum is regarded as the earliest widespread complex trace fossil

Trace fossil

Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...

. It's earliest appearance, which was contemporaneous with the last of the Ediacaran biota, is used to define the dividing line between the Ediacaran

Ediacaran

The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...

 and Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

 Periods.
However, it has since been discovered below the originally defined global boundary stratotype section

Global Boundary Stratotype Section and Point

A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon stratigraphic section which serves as the reference section for a particular boundary on the geologic time scale. The effort to define GSSPs is conducted by the International Commission on...

.

Treptichnus pedum has a fairly complicated and distinctive burrow

Burrow

A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...

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

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

 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 fossil

Trace fossil

Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...

s, which occur worldwide, are usually found in strata

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

 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

Bone

Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

s. Its morphology

Comparative anatomy

Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...

 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)".