Upper Keuper  The Upper Keuper (, also Oberkeuper, Rhätkeuper, Rätkeuper) or Rhätsandstein ("Rhätsandstein") is a lithostratigraphic subgroup of the Keuper in the Germanic Trias. It currently has only one formation, the Exter Formation. The lithostratigraphic unit is underlain by the Middle Keuper subgroup and overlain, in the North German Basin, by the Lias and, in the South German Basin by the Black Jurassic. The Exter is a Mesozoic geologic formation. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation.