A group of living things
Amniotes
Amniota
The family that carries its own pond.
Its members' last common ancestor lived about 320 million years ago.
You are part of this group. See how.
A waterproof egg helped this family breed away from water, and you belong to it. Inside such an egg, the baby floats in its own little pond of fluid, and the shell slows drying while still letting air in. Most reptiles and all birds lay these eggs on land today, which helped the family breed and live in drier places than their amphibian cousins.
This one family holds scaly reptiles, feathered birds and furry mammals. Mammals form one branch, while reptiles and birds form the other. Birds are living dinosaurs, so even a hummingbird counts as one. Lizards, turtles, crocodiles and birds share the same plan of head, trunk, tail and four limbs. Humans share it too, except we have only a tiny tailbone inside.
Their skin is dry and water-saving, never slimy, and they breathe with the help of rib muscles. Dry skin and the waterproof egg helped amniotes spread far from the shore. Today they live almost everywhere, from deserts and grasslands to oceans, mountains and city parks.
Only five living mammals lay eggs
The platypus and four echidnas are the only living mammals that lay eggs. The mothers feed milk through many pores on the belly, which the babies lap up.
Biggest and smallest
Amniotes range from about 2 grams to about 180 tonnes. One of the smallest is the bumblebee bat, about the size of a large bumblebee. A blue whale can reach about 29 metres, longer than a bus. Even a newborn is about 7 to 8 metres long, longer than a car.
The sail-back was not a dinosaur
Dimetrodon, the sail-backed animal often shown with dinosaurs, was not a dinosaur or a lizard. It was an early relative on the mammal side of the family and lived before the first dinosaurs.