Placentari

Placentari, commonly known in English as Placentalia, is a clade of mammals comprising all living placental mammals and their extinct relatives, excluding monotremes and marsupials. The defining feature is a complex placenta that nourishes the embryo during a relatively long gestation.

Most placentals are viviparous with a chorioallantoic placenta formed between fetal membranes and the maternal uterus. They exhibit a wide range of body sizes and ecological niches, and their developmental strategies vary from precocial to altricial young. A typical anatomical trait among many placentals is the relative reduction or absence of epipubic bones, though some stem lineages retain them.

Origin and diversification: The clade likely originated in the Late Jurassic to Early Cretaceous, with the exact timing debated among researchers. The major diversification of living placental orders occurred after the Cretaceous–Paleogene extinction event about 66 million years ago, leading to the spread of lineages such as Afrotheria (elephants, manatees), Xenarthra (sloths, armadillos), Euarchontoglires (primates, rodents, lagomorphs), and Laurasiatheria (bats, carnivores, hoofed mammals) across most continents.

Notes: Placentari is a large and diverse group, and taxonomic definitions can vary among sources. Fossil evidence and molecular data continue to refine the understanding of relationships within the clade and the timing of key divergence events. The group includes humans and most other living mammals.