Prototherian

It is evident that the Edentates are widely separated from all other existing Eutherians; and Professor W. K. Parker, in view of the tendency to a variation in the number of cervical vertebræ and other features, has suggested a separate origin from a Prototherian stock.

In his classification of prototherian mammals Hopson (31) queried the allocation of Haramiyidae to the Multituberculata and suggested that multituberculates were derived from a morganucodontid ancestry.

[…]the modern remaining prototherian lines are the Australian and New Guinean monotremes, egg-laying mammals now represented by the grub- and shrimp-eating platypus (Ornithorhyncus) and ant-eating echidna (Tachyglossus and Zaglossus).

Monotremes (prototherians), which include the duck-billed platypus, and short- and long-beaked echidnas, have a cloaca—a single opening for the fecal, urinary, and reproductive tracts.