Psilonichnus Fürsich, 1981 in its type-locality (Praia do Salgado, western Portugal)

The ichnogenus Psilonichnus was described 35 years ago by Franz Theodor Fürsich at the Late Jurassic of “Cliff south of Salgados”. These forms are preserved in high transgressive system tracts that, in the type-locality, show the typical diagnostic features of the Psilonichnus Ichnofacies, almost solely represented by dense ichnofabrics of branched and unbranched forms attributed to Psilonichnus. In stiffgrounds, J-shaped burrows with terminal chambers and chela imprints are closer related to Macanopsis. Both trace fossils may have a probable brachyuran origin that, however, predates the brachyuran body fossil and provide some of the earliest ecological evidence of the physiological adaptation of crabs to survive in a quasiterrestrial environment. They were certainly multipurposed burrows, serving as dwelling structures, refuges from predators, but there are also evidences as places for copulate on and brooding, contributing for the understanding of the evolution of mating behaviour recorded in the geological time.