Internal structures of trilobite trace fossils indicative of an open surface furrow origin
Abstract X-radiography of sections cut from Cruziana and Rusophycus of Cambro-Ordovician age, show that they contain cross-laminated, parallel-laminated, pelleted and homogenous fills. The absence of bioturbation or mottling textures and the undisturbed nature of the primary sedimentary structures does not support a burrow origin for these trilobite-produced trace fossils. An open surface furrow origin is supported both by the presence of internal primary sedimentary structures and by the precise current orientation of many of these types of trace fossils.