cladotheria (also called zatheria) is a clade of mammals—that means a group of mammals who all evolved from the same ancient creature. cladotheria has marsupials, placentals, and some kinds of extinct animals like dryolestoids, amphitheriids and peramurids. this clade was named in 1975 by malcolm mckenna. in 2002, scientists called it a node-based taxon that had "the common ancestor of dryolestids and living therians, plus all its descendants". a different definition was written in 2013. then scientists said that cladotheria has all groups of mammals that are more like a house mouse than they are like the animal spalacotherium tricuspidens.