Rusophycus

Rusophycus is an ichnogenus of trace fossils representing resting traces produced by trilobites on soft sediment surfaces in ancient marine environments. It is among the best-known trilobite-related ichnofossils and is widely recorded in Paleozoic rocks around the world.

Morphology commonly consists of a shallow, broad depression with a rounded to oval outline. The trace records the trilobite's settle-and-rest posture, with the cephalon and thorax pressed into the sediment. In some specimens, faint longitudinal or lateral furrows reflect limb impressions or axial part movements; in others the impression is smoother, making interpretation more tentative.

Rusophycus is an ichnogenus subdivided into numerous ichnospecies, which reflect variations in posture, substrate, and preservation. It is contrasted with Cruziana, the signature trace of trilobite locomotion, which records active movement across the surface.

Significance lies in its use for behavioral and paleoenvironmental inference. Rusophycus indicates relatively calm, fine-grained substrates suitable for trilobite resting and helps correlate strata with trilobite assemblages. It is widely distributed in Cambrian to Paleozoic marine deposits and forms a key part of ichnologic studies of early animal life.