Amniote

Some animals live on land.

They have special parts inside their eggs. These parts keep the babies safe. The parts also help them breathe.

These animals do not need water for babies. They can lay eggs on dry ground. This helps them live in many places.

Their skin is also thick. This helps them stay on land. Some of them have bones in their ankles to help them move.

This group includes birds and reptiles. It also includes humans!

It is amazing how they live on land.

Amniotes are a large group of animals. This group includes humans, birds, and reptiles.

Long ago, these animals moved from water to land. They changed to live in dry places. One big change was how they make babies. Most fish and frogs must lay eggs in water. But amniotes can lay eggs on dry ground.

Inside the egg, there are special parts called membranes. The amnion is a sac that protects the baby. The chorion helps the baby breathe air. The allantois stores waste. These parts let the eggs grow much larger. Larger eggs mean the babies can grow into big adults.

Other body parts helped them live on land, too. They have thick skin to keep water inside. They also have an astragalus. This is a special bone in the ankle. It helps them move their feet better.

Early amniotes looked like small lizards. They lived a very long time ago. Some lived during the Carboniferous period. Others may have lived even earlier. These changes helped them become the main animals on land.

Amniotes are a huge group of animals that live on land. This group includes humans, birds, and reptiles like the Nile crocodile. They are special because they can live far away from water. Most other land animals, like frogs, must stay near wet places to survive. Amniotes made a big jump in history by moving from water to land. This change helped them become the main animals living on Earth.

The way amniotes grow is very clever. They use three special membranes, or thin layers, to protect their babies. The amnion is a sac that keeps the embryo safe. The chorion helps the baby breathe by swapping gases. The allantois is a part that stores waste. These parts allow eggs to be much larger than frog eggs. Larger eggs mean babies can grow into much bigger adults.

Scientists have studied these animals for a long time. An embryologist named Ernst Haeckel first described them in 1866. He named them after the amnion membrane. The word comes from a Greek word for a membrane. It even comes from a word meaning "lamb." This name helps us remember how they protect their young.

These animals appeared a very long time ago. Fossils show they lived during the Carboniferous period. Some footprints in Australia suggest they lived even earlier. These prints are from the Snowy Plains Formation. They are about 358 to 354 million years old. Early amniotes quickly split into two main groups. One group led to mammals, and the other led to reptiles and birds.

You can see how amniotes are different from frogs. Frogs have to lay eggs in water to keep them wet. Amniotes have thick skin to keep water inside their bodies. They also have a special bone in their ankle called an astragalus. This bone helps them move their feet better on land. They use their ribs to help them breathe air. All these parts work together to let them explore the dry world.

Amniotes are a massive group of vertebrate animals known as tetrapods. This group includes almost all living creatures that live on land or in semiaquatic environments. Humans, birds, and the Nile crocodile are all members of the clade Amniota. This group represents a massive leap in the history of life on Earth. It marks the moment when vertebrates moved from living in water to living fully on land.

The secret to this success is the amniotic egg and its special membranes. Unlike fish or amphibians, amniotes use three extraembryonic membranes to protect their young. The amnion is a sac that surrounds and protects the embryo from environmental changes. The chorion is a membrane that allows for gas exchange between the embryo and the air. The allantois serves as a way to store or dispose of metabolic waste. These membranes allow amniotes to reproduce on dry land without needing a pond or lake.

Because of these membranes, amniotes have several different ways to have babies. Some lay shelled eggs on land, which is called oviparity. This is common in birds and most reptiles. Some reptiles use ovoviviparity, where they keep shelled eggs inside the mother until they hatch. Other animals, like most mammals, use viviparity to nurture fertilized eggs inside the mother's body. These different strategies help amniotes survive in many different environments.

To survive on land, amniotes also developed many physical changes. They have thicker, keratinized skin that prevents water loss. They use costal respiration, which means they breathe by expanding and contracting their rib cage. They also have more complex kidneys and specialized tissues near their kidneys for managing body chemistry. An important bone called the astragalus in the ankle allows for a better range of motion in their limbs. These traits allow them to move and breathe efficiently in dry air.

Scientists have been studying these animals for many years. The embryologist Ernst Haeckel first formally described amniotes in 1866. He named the group after the amnion membrane. The name comes from the Greek word "amnion," which refers to the membrane surrounding a fetus. Interestingly, the word is also linked to the Greek word for "lamb."

The history of amniotes is written in the ancient rocks of the Earth. For a long time, scientists thought they appeared during the Carboniferous period. However, fossilized footprints found in Australia's Snowy Plains Formation changed this view. These prints are between 358.9 and 354 million years old. This suggests that amniotes may have actually originated even earlier, during the Devonian period.

Early in their history, amniotes split into two major groups. One group is the sauropsids, which includes all reptiles and birds. The other group is the synapsids, which includes mammals and their extinct ancestors. We can tell these groups apart by looking at the skull. Synapsids have one hole behind each eye, while diapsids, like birds and crocodiles, have two. Turtles are also diapsids, even though they seem to have no holes in their skulls.