Mammaliaformes ("mammal-shaped") is a clade that contains the mammals and their closest extinct relatives. Phylogenetically it's defined as a clade including the most recent common ancestor of Sinoconodon, morganuconodonts, docodonts, Monotremata, Marsupialia, Placentalia, extinct members of this clade, and all of its descendants. The precise phylogeny is disputed due to the scantness of evidence in the fossil record. However, it's thought that the Mammaliaformes were of three major groups: All… (More on Mammaliaformes)