A new Isochirotherium trackway from the Triassic of Vieux Emosson, SW Switzerland: stratigraphic implications

The footprint assemblage of Vieux Emosson, located at 2400 m altitude in the Swiss Alps, was first described in 1982. The assemblage was regarded as Late Ladinian or Carnian in age, but the dating was questioned because the taxa show few affinities with other Triassic assemblages. Here we describe a short trackway with shallow but well-preserved tracks referred to the ichnogenus Isochirotherium, showing affinities with Isochirotherium soergeli and Isochirotherium lomasi. The trackway is present on a piece of slab ex situ lying on a mass of fallen rocks, but the slab can be attributed with confidence to the same level as the main one previously mapped. Preliminary observations in situ and of the footprint casts made in 1979 and deposited in the Natural History Museum of Geneva suggest that none of these are attributable to dinosaurs and that the Vieux Emosson footprints are mainly track preservation variations of chirotherian tracks. The occurrence of the ichnogenus Isochirotherium favours an older age, probably Early or Middle Triassic, than previously suggested for the Vieux Emosson tracksite.