Prototheria

The prototheria (Prototheria) are a subclass of mammals whose taxonomic hierarchy is somewhat controversial, especially in relation to the non-hierarchical class Australosphenida. It includes mainly fossil species and 5 living species: the platypus and the four species of echidnas

Phylogeny

The following is a simplified cladogram based on the work of McKenna and Bell and Kielan-Jaworowska et al.: