placental

(adjective)

a mammal having a placenta; most members of Mammalia

Related Terms

Examples of placental in the following topics:

  • Living Mammals

    • The eutherians, or placental mammals, and the metatherians, or marsupials, together comprise the clade of therian mammals.
    • Marsupials differ from eutherians in that there is a less complex placental connection.
    • There are 18 to 20 orders of placental mammals.
    • Eutherian mammals are sometimes called placental mammals because all species possess a complex placenta that connects a fetus to the mother, allowing for gas, fluid, and nutrient exchange.
    • Red foxes are eutherian (placental) mammals because the mothers nourish their young via a placenta during fetal development.

  • Evolution of Mammals

    • 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).
    • Metatherians are the animals more closely related to the marsupials, while eutherians are those more closely related to the placentals.
    • One of the major differences between placental and nonplacental eutherians is that placentals lack epipubic bones, which are present in all other fossil and living mammals (marsupials and monotremes).
    • After the Cretaceous–Paleogene extinction event wiped out the non-avian dinosaurs (birds are generally regarded as the surviving dinosaurs) and several other 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.

  • Fertilization

    • In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane .

  • Cleavage, the Blastula Stage, and Gastrulation

    • In placental mammals (including humans) where nourishment is provided by the mother's body, the eggs have a very small amount of yolk and undergo holoblastic cleavage.

  • Biogeography

    • Most of New Guinea, as another example, lacks placental mammals.

  • Primates

    • Primates are one of the oldest of all surviving placental mammal groups.