A group of living things
Placental mammals
Placentalia
Long pregnancies, from bumblebee-sized bats to blue whales
Its members' last common ancestor lived about 95 million years ago.
You are part of this group. See how.
Placental mammals grow their babies inside the mother, often for a long time. A special organ called the placenta passes food and oxygen from the mother's blood to the baby. Their closest relatives, the marsupials, give birth very early to tiny, helpless babies that keep growing attached to the mother, often in a pouch.
This is the largest mammal group, with about 6,000 kinds. Most are rodents or bats. It also includes whales, elephants, dogs, cats, horses and humans. Sizes run from a bat about as big as a bumblebee to the blue whale, the largest animal known to have lived, longer than two buses.
Between them, they live almost everywhere: on land, in fresh water, in the sea and in the air. Mothers feed their babies with milk. Bats are the only mammals that truly fly, while whales live, breed and rest entirely in water.
The longest pregnancy on land
African elephants carry their babies for about 22 months, the longest pregnancy of any land mammal. The baby is born well grown and can soon walk long distances.
Whales once lived on land
Whales, dolphins and porpoises evolved from mammals that lived on land.
A misleading name
Marsupials also grow a placenta, but theirs is short-lived and feeds the baby far less than the complex placenta of placentals.
Inside placental mammals
- African bush elephantThe largest land animal; its nearest living relatives include manatees and hyraxes.
- Primates, rodents and rabbitsYour branch of the mammals: a mouse is a closer cousin of yours than a dog is.
- Bats, carnivores and hoofed mammalsA surprising family: bats, cats, horses and whales share one ancestor.