Rusophycus is a trace fossil allied to Cruziana

Cruziana

Cruziana is a trace fossil consisting of elongate, bilobed, approximately bilaterally symmetrical burrows, usually preserved along bedding planes, with a sculpture of repeated striations that are mostly oblique to the long dimension...

. Rusophycus is the resting trace, recording the outline of the tracemaker; Cruziana is made when the organism moved. Both are typically associated with trilobites but can also made by other arthropods.

Rusophycus is known from sediments dating right to the base of the Cambrian , long before the earliest trilobite fossils, and from the Triassic (after the Permian extinction of trilobites), indicating that other producers could make the trace.