1. The most recent phylogenetic studies recover it as actually a paraphyletic assemblage leading to Placentalia . 2. The older system was essentially the same, but used the names Monotremata, Marsupialia, and Placentalia . 3. Viviparous mammals are in the subclass Theria; those living today are in the Marsupialia and Placentalia infraclasses. 4. The date of divergence of " Protungulatum " and " Placentalia " is approximately 75 Ma. 5. The Prototheria-Metatheria-Eutheria system has a number of miniscule differences from the Monotremata-Marsupialia-Placentalia system. 6. Eutheria was named in 1872 by Theodore Gill; in 1880 Thomas Henry Huxley defined it to encompass a more broadly defined group than Placentalia . 7. The two infraclasses of Theria in the Prototheria-Theria system may also be " Marsupialia " and " Placentalia ". 8. Huxley s system, in which The three subclasses are Prototheria, Metatheria, and Eutheria, rather than Monotremata, Marsupialia, and Placentalia . 9. The function of this organ is probably to transfer nutrients from the mother; however the structure is small, compared to those of the Placentalia . 10. Either because the last common ancestor of Placentalia was nocturnal and had no use for good color vision, or simply because it just so happened.
