extinct genus of primitive, probably predaceous, mammals (mammal) known from fossils (fossil) found in European deposits dating from the late Jurassic (Jurassic Period) and early Cretaceous periods (Cretaceous Period) (some 160 million –100 million years ago). The genus Spalacotherium has a symmetrodont dentition, characterized by molar teeth with three cusps arranged in a triangle. The symmetrodonts are among the oldest known mammals and also among the most common European faunas of the time.