Giant Paleodictyon in Eocene flysch
Abstract A giant Paleodictyon gomezi with a maximum mesh diameter of 13 cm and covering more than 0.5 m2 occurs in the lower Eocene flysch near Zumaya. The giant Paleodictyon occurs with flute casts and, therefore, must have been produced deeply in the sediment. The lengthening of mesh cells parallel and perpendicular to the flute casts implies changing current directions during trace production. Rows of elongate and offset mesh cells reflect the row-by-row production of the trace; however, the base line followed by the trace fossil producer (meandering or spiral) cannot be reconstructed because of incomplete preservation. The extraordinary size of this giant Paleodictyon contradicts the evolutionary trend of deep-sea trace fossils toward optimization and miniaturization, since similar large Paleodictyon specimens occur in Silurian flysch.