Placental in the context of "Cenozoic"

Palaeosinopa is an extinct genus of semi-aquatic, placental eutherian mammals belonging to the family Pantolestidae. Their diet consisted of other semi-aquatic life forms.

Armadillos (Spanish for 'little armored ones') are New World placental mammals in the order Cingulata. They form part of the superorder Xenarthra, along with the anteaters and sloths. 21 extant species of armadillo have been described, some of which are distinguished by the number of bands on their armor. All species are native to the Americas, where they inhabit a variety of environments.

Living armadillos are characterized by a leathery armor shell and long, sharp claws for digging. They have short legs, but can move quite quickly. The average length of an armadillo is about 75 cm (30 in), including its tail. The giant armadillo grows up to 150 cm (59 in) and weighs up to 54 kg (119 lb), while the pink fairy armadillo has a length of only 13–15 cm (5–6 in). When threatened by a predator, Tolypeutes species frequently roll up into a ball; they are the only species of armadillo capable of this.

Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well as many extinct non-marsupial relatives. It is one of two groups placed in the clade Theria alongside Eutheria, which contains the placentals. Remains of metatherians have been found on all of Earth's continents.

The Cenozoic Era (also known as the Caenozoic, Kainozoic, or Neozoic Era; /ˌsiːnəˈzoʊ.ɪk, ˌsɛn-/; SEE-nə-ZOH-ik, SEN-ə-; lit. 'new life') is Earth's current geological era, representing the last 66 million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three geological eras of the Phanerozoic Eon, preceded by the Mesozoic and Paleozoic. The Cenozoic started with the Cretaceous–Paleogene extinction event, when many species, including the non-avian dinosaurs, became extinct in an event attributed by most experts to the impact of a large asteroid or other celestial body, the Chicxulub impactor.

The Cenozoic is commonly known as the Age of Mammals because the terrestrial animals that dominated both hemispheres were mammals – the eutherians (placentals) in the Northern Hemisphere and the metatherians (marsupials, now mainly restricted to Australia and to some extent South America) in the Southern Hemisphere. The extinction of many groups allowed mammals and birds to greatly diversify so that large mammals and birds dominated life on Earth. The continents also moved into their current positions during this era.

A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is not homologous with the coracoid bone of most other vertebrates.

In other tetrapods, it joins the scapula to the front end of the sternum and has a notch on the dorsal surface which, along with a similar notch on the ventral surface of the scapula, forms the socket in which the proximal end of the humerus (upper arm bone) is located. The acrocoracoid process is an expansion adjacent to this contact surface, to which the shoulderward end of the biceps brachii muscle attaches in these animals. In birds (and generally theropods and related animals), the entire unit is rigid and called scapulocoracoid. This plays a major role in bird flight. In other dinosaurs, the main bones of the pectoral girdle were the scapula (shoulder blade) and the coracoid, both of which directly articulated with the clavicle.

The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes. Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, the earliest known eutherian, lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.

After the Cretaceous–Paleogene extinction event wiped out the non-avian dinosaurs (birds being the only surviving dinosaurs) and several mammalian groups, placental and marsupial mammals diversified into many new forms and ecological niches throughout the Paleogene and Neogene, by the end of which all modern orders had appeared.

Cingulata, part of the superorder Xenarthra, is an order of armored New World placental mammals. The armadillos, whose species are split between the families Dasypodidae and Chlamyphoridae, are the only surviving members of the order. Two groups of cingulates much larger than extant armadillos (maximum body mass of 45 kg (100 lb) in the case of the giant armadillo) existed until recently: pampatheriids, which reached weights of up to 200 kg (440 lb) and chlamyphorid glyptodonts, which attained masses of 2,000 kg (4,400 lb) or more.

The cingulate order originated in South America during the Paleocene epoch about 66 to 56 million years ago, and due to the continent's former isolation remained confined to it during most of the Cenozoic. However, the formation of a land bridge allowed members of all three families to migrate to southern North America during the Pliocene or early Pleistocene as part of the Great American Interchange. After surviving for tens of millions of years, all of the pampatheriids and giant glyptodonts apparently died out during the Quaternary extinction event at the beginning of the Holocene, along with much of the rest of the regional megafauna, shortly after the colonization of the Americas by Paleo-Indians.