Prototheria (próto-thiŕ ee-a) (Gr.prōtos, first, + thēr, wild animal) is the subclass to which the order Monotremata belongs. In biology, a subclass is one level below a class. ... Families Kollikodontidae(extinct) Ornithorhynchidae- Platypus Tachyglossidae- Echidnas Steropodontidae(extinct) Monotremes (monos, single + trema, hole; refers to the cloaca) are mammals that lay eggs, instead of giving birth to live young like marsupials (Metatheria) and placental mammals (Eutheria). ...

Most of the animals in this subclass came from the Cretaceous and early Cenozoic period, which are all extinct now except for the egg laying monotremes. One such animal is the Duck-billed platypus. Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period, about 146 million years ago (Ma), to the beginning of the Paleocene epoch of the Tertiary period (65. ... The Cenozoic Era (sen-oh-ZOH-ik; sometimes Caenozoic Era in the United Kingdom) meaning new life (Greek kainos = new + zoe = life) is the most recent of the three classic geological eras. ... Binomial name Ornithorhynchus anatinus (Shaw, 1799) The Platypus (Ornithorhynchus anatinus) is a small, half-aquatic mammal endemic to the eastern part of Australia, and one of the three extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young (the other two are echidnas). ...

Since Monotremata is the only order currently in the subclass Prototheria, it seems somewhat redundant. However, it is always possible that fossils will come to light placing creatures of some other order in that group, and Prototheria is often used in contrast to the two other subclasses, Marsupialia and Placentalia (or, in more modern scientific terms, Metatheria and Eutheria). These three subclasses; Prototheria, Metatheria, and Eutheria; mean "first beast", "intermediary beast", and "true beast". The names were first proposed by Thomas Huxley. Metatheria and Eutheria are often grouped as magnorders of the subclass Theria. Orders Superorder Ameridelphia Didelphimorphia Paucituberculata Superorder Australidelphia Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Marsupials are mammals in which the female typically has a pouch (called the marsupium, from which the name Marsupial derives) in which it rears its young through early infancy. ... Orders Superorder Xenarthra: Pilosa Cingulata Infraclass Epitheria: Superorder Afrotheria: Afrosoricida (Golden mole and tenrec) Macroscelidea (Elephant shrew) Tubulidentata (Aardvark) Hyracoidea (Hyrax) Proboscidea (Elephant) Sirenia (Manatee, Dugong) Superorder Laurasiatheria: Chiroptera (Bats) Insectivora (Shrews, Moles) Cetacea (Whale, dolphin) Artiodactyla (Ruminants et al) Perissodactyla(Horse et al. ... Metatheria is a grouping within the animal class Mammalia. ... Eutheria is a taxon (specifically, an infraclass) nearly synonymous with Placentalia, containing the placental mammals and the nearest ancestors of placental mammals (which are known only from the fossil record). ... Thomas Huxley Thomas Henry Huxley F.R.S. (May 4, 1825 – June 29, 1895) was a British biologist, known as Darwins Bulldog for his defence of Charles Darwins theory of evolution. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Infraclasses Eutheria Metatheria Theria is a subclass of advanced mammals that give birth to live young without using a shelled egg. ...