A group of living things
Reptiles and birds
Sauropsida
Birds are reptiles too
Its members' last common ancestor lived about 280 million years ago.
You and reptiles and birds last shared an ancestor about 320 million years ago (on 4 December, if life's history were one year).
Birds belong in this family. A sparrow is a closer relative of a crocodile than a crocodile is of a lizard. That is because birds grew from meat-eating dinosaurs. When an asteroid ended the age of the dinosaurs about 66 million years ago, the bird line lived on, so every garden bird is a living dinosaur.
Dry skin links the group. Most have small, horny scales, while birds have feathers with scales on the legs and feet. Scales, claws, feathers and the outer covering of beaks contain the same tough protein, keratin. Most members lay eggs that can develop away from water, with the young held safe in fluid inside thin skins. Hard-shelled bird eggs and the softer, leathery eggs of many turtles work in a similar way.
They live almost everywhere, from deserts and gardens to rivers and open sea. Sizes run from a tiny lizard shorter than your thumb to a crocodile longer than a family car. Lizards, snakes, turtles, crocodiles and alligators warm up by basking in the sun, while feathered birds make their own heat inside.
Thousands of species
Scientists have listed about 12,000 species of lizards, snakes, turtles, crocodiles and their relatives, and about 11,000 bird species live in the world today. New species are still described each year, so the totals keep changing.
A shell you cannot remove
A turtle cannot climb out of its shell. The shell is its ribs and backbone grown together, with the shoulders and hips tucked inside the ribs.
Teeth that keep coming
Crocodiles and alligators swim with a strong, flat tail and wear bony plates in the skin of the back. An alligator holds about 74 to 80 teeth at once and may grow about 3,000 in a lifetime.