Palaeognathae

Some birds are very special.

Most of them cannot fly. They stay on the ground.

These birds include the ostrich and the emu.

They also include the kiwi.

One type of bird in this group can fly. It is called a tinamou.

These birds have old jaws. This means their mouth bones are shaped in an old way.

They are a very interesting group of birds.

Paleognaths are a special group of birds.

Their name means "old jaws." This refers to the bones in their mouths. These bones look like the jaws of old reptiles.

Most of these birds cannot fly. We call these flightless birds ratites. This group includes the big ostrich.

It also includes the rhea and the emu. You can find kiwis and cassowaries too.

One group can still fly. These are the tinamous.

Some paleognaths are now extinct. The moa and the elephant bird are gone.

Scientists use DNA to study them. DNA is the code inside living things. This helps us see how they changed over time. It shows that flightlessness happened many times. Some birds became flightless on their own. This is called parallel evolution.

This fossil shows an old flying bird. It helps us learn about their past.

Paleognaths are a very special group of birds.

Their name comes from Ancient Greek words meaning "old jaws." This name describes the bones in their mouths. These bones look more like the jaws of reptiles than other birds.

Most of these birds are part of a group called ratites. Ratites are birds that cannot fly. They often grow to be very large. One group that can still fly is the tinamous.

Scientists study them to learn how birds changed over millions of years.

How these birds live and change is quite interesting. Many ratites live in places like the southern landmasses. These birds once flew to these areas. After they arrived, they stopped flying. This happened more than once in their history. This way of changing is called parallel evolution.

It means different groups developed the same trait on their own. Some birds even grew to be huge. This is called gigantism. They changed to fit their new homes.

People have studied these birds for a long time. In 1813, a person named Merrem used the name "Ratitae." Later, in 1900, Pycraft used the term "Palaeognathae." He was very smart about how they were grouped. He knew that flightless birds could be related in different ways. He looked at their skeletons to find the truth. He also studied their internal organs. This helped scientists understand their family tree.

There are many different kinds of paleognaths today. There are 47 species of tinamous.

You can find five species of kiwis.

There are three species of cassowaries. You might also see one species of emu. There are two types of rheas.

Finally, there are two types of ostriches.

Some, like the moa and elephant bird, are now extinct.

We can learn about these birds by looking at fossils and DNA. Fossils are bones left in the ground from long ago. One fossil called *Lithornis* shows a bird that could fly.

Scientists also look at DNA, which is the code inside living things. DNA helps us see how long ago these birds split apart. Some studies say they began to change 110 to 120 million years ago. This was during the Early Cretaceous period. Even though they look different, their DNA shows they belong together. They are a single, natural group of birds.

Palaeognathae is a major group of birds within the class Aves. This group is one of two main lineages of living birds. The other group is called Neognathae. The name "paleognath" comes from Ancient Greek words meaning "old jaws."

This refers to the specific anatomy of their palate. Their skeletal structure in the mouth is considered more primitive. It looks more like the jaws of reptiles than those of other birds. Scientists study these birds to understand how different species evolved over millions of years.

To understand how these birds work, we must look at their physical traits. Most paleognaths are part of a group called ratites. Ratites are characterized by being flightless. They often lack a keeled sternum, which is the breastbone used to attach flight muscles. However, not all paleognaths are flightless. The tinamous are a flying lineage within this group.

Recent genetic research shows that flightlessness did not happen just once. Instead, it arose multiple times through parallel evolution. This means different lineages independently lost the ability to fly as they adapted to new environments.

There are five main orders of living paleognaths today. The tinamous include 47 different species.

The kiwis consist of five species.

There are three species of cassowaries. The emus include one species, though another became extinct in recent history. The rheas include two species.

Finally, the ostriches consist of two species.

These birds vary greatly in size and appearance.

History and discovery have shaped how we classify these birds. In 1813, Merrem used the term "Ratitae" to group them.

Later, in 1900, Pycraft introduced the term "Palaeognathae." Pycraft made an important discovery in how scientists view these birds. He realized that a flightless anatomy could evolve in unrelated birds. This meant they should not be grouped together just because they cannot fly. He used the anatomy of the palate and other organs to create a more accurate classification. This helped move science away from simple groupings based only on flight.

Fossil evidence provides a timeline for these birds. While no unambiguous fossils exist from very early periods, many researchers believe they evolved during the Cretaceous period.

Some studies suggest they began to diverge 110 to 120 million years ago. However, there is a gap in the fossil record of about 45 million years. We do not have many fossils from the period between 70 and 115 million years ago. Fossils like *Lithornis* show us birds that could still fly.

These fossils help scientists trace how the group moved from the Northern Hemisphere to the southern landmasses.

Many paleognaths are now extinct, providing surprising facts about their past. The Dinornithiformes, known as moas, lived in New Zealand.

The Aepyornithiformes, or elephant birds, were also large and lived in different areas.

Both of these groups became extinct within the last 1,250 years. These extinct birds show that paleognaths often underwent gigantism. Gigantism is when animals evolve to become much larger than their ancestors. This often happens when birds occupy environments where they no longer need to fly to escape predators.

Today, scientists use DNA analysis to connect these birds to the broader tree of life. Molecular studies look at specific genes to see how closely species are related. This research has changed our understanding of the group's history. For example, DNA shows that tinamous are actually quite advanced, not primitive.

It also shows that the divergence of paleognaths is one of the oldest events in bird history. By studying these connections, we learn how life on Earth changes through constant adaptation and evolution.