In elevating the marsupials to the rank of a sub-class the name Metatheria has been suggested as the title for the higher grade, with Marsupialia as the designation for the single order by which they are now represented.
It is, however, less liable to cause confusion, and in many other ways more convenient to employ the better known term Marsupialia in both senses.
Thomas, Catalogue of Monotremata and Marsupialia in the British Museum (1888); "On Caenolestes, a Survivor of the Epanorthidae," Proc. Zool.
Bensley, "A Theory of the Origin and Evolution of the Australian Marsupialia," American Naturalist (1901); "On the Evolution of the Australian Marsupialia, &c.," Trans.
P. Hill, "Contributions to the Morphology of the Female Urino-genital Organs in Marsupialia," Proc. Linn.
And xxv.; "Contributions to the Embryology of the Marsupialia," Quart.
There are two orders, the Marsupialia and the Monotremata, which do not possess this organ; both these are found in Australia, to which region indeed they are not absolutely confined.
Orders: Bimana, Quadrumana, Carnivora, Marsupialia, Rodentia, Edentata, Pachydermata, Ruminantia, Cetacea.
Orders: (a) Monodelphia: Bimana, Quadrumana, Cheiroptera, Insectivora, Rodentia, Edentata, Carnivora, Amphibia, Pachydermata, Ruminantia, Cetacea; (b) Didelphia: Marsupialia, Monotremata.
Marsupialia (q.v.) (Metatheria).
We are dependent upon the Carnivora, Rodentia, Ungulata and Marsupialia for our supplies of furs, the first two classes being by far of the greatest importance.
The Carnivora include bears, wolverines, wolves, raccoons, foxes, sables, martens, skunks, kolinskis, fitch, fishers, ermines, cats, sea otters, fur seals, hair seals, lions, tigers, leopards, lynxes, jackals, &c. The Rodentia include beavers, nutrias, musk-rats or musquash, marmots, hamsters, chinchillas, hares, rabbits, squirrels, &c. The Ungulata include Persian, Astrachan, Crimean, Chinese and Tibet lambs, mouflon, guanaco, goats, ponies, &c. The Marsupialia include opossums, wallabies and kangaroos.
Near affinity; and while more nearly related to the Marsupialia (q.v.), in which an imperfect allantoic placenta is sometimes developed, it is broadly distinguished therefrom by the invariable presence of a functional placenta by the aid of which the foetus is nourished throughout the greater portion of intra-uterine life.
- That mammals have become differentiated from a lower type of vertebrates at least as early as the commencement of the Jurassic period is abundantly testified by the occurrence of the remains of small species in strata of that epoch, some of which are mentioned in the articles Marsupialia and Monotremata.
Most of the earliest known mammals appear to be related to the Marsupialia and Insectivora.