Therapsida

These animals were like our old kin.

They lived a long time ago. They had legs that stood under them. This helped them walk well.

Their teeth were very special too. Some teeth were for nipping. Other teeth were for tearing food. Some teeth were for chopping food.

Some had skin like an elephant. Others may have had hair. These animals led to us! They are the ancestors of mammals.

Therapsids were a large group of animals. They lived a long time ago. They are the ancestors of all mammals.

These animals changed how they moved. Most reptiles have legs that sprawl out to the sides. Therapsids had legs that stood more underneath their bodies. This gave them a more mammal-like way of walking.

Their teeth also changed. Some had teeth for nipping. Others had large teeth for tearing. Some had teeth for chopping food.

Their skin was also different. Some may have had hair. Other fossils show skin that looks like an elephant.

One group called cynodonts lived a long time. They led to the first mammals. Most other groups died out later. This happened after a big extinction event. The dinosaurs soon became the main animals on land. Today, the only living therapsids are mammals.

Therapsids were a huge group of animals that changed the world. They are the ancestors of all mammals living today.

Long ago, they were the most common large animals on land. They lived during a time called the Permian period. Most reptiles have legs that sprawl out to the sides. Therapsids were different because their legs stood more underneath their bodies. This helped them walk in a way that looks more like a mammal.

These animals had many special ways of living and eating. Their jaws became much stronger and more complex over time. They had different types of teeth for different jobs. Some teeth were incisors used for nipping at food. They had large canine teeth for puncturing and tearing. Other teeth were molars used for shearing and chopping.

Their bodies also began to change how they stayed warm. Some early therapsids had a small hole in their skull for a special eye. This eye helped them manage their body heat. Later groups lost this eye as they changed.

Scientists have studied these animals for a long time. In 1986, two researchers named Hopson and Barghausen shared a new way to group them. They suggested a plan for how these animals were related.

This plan is called the Hopson and Barghausen paradigm. It helped people understand the different branches of the therapsid family tree. One branch is called Biarmosuchia, which was recognized as its own group later. Other groups like the dinocephalians lived and died out in the Middle Permian. Studying these old bones helps us see how life moves forward.

Therapsids lived through many big changes in Earth's history. They first appeared more than 279.5 million years ago. They grew very successful until a massive extinction event happened. This event was called the Permian–Triassic extinction event. After this, many groups like the gorgonopsians died out completely.

Other groups like the dicynodonts survived for a while longer. The dicynodonts were herbivores that lived until the end of the Triassic. Around 225 million years ago, a group called cynodonts began to lead to mammals. These were the only therapsids to survive past the end of the Triassic.

We can see how therapsids connect to the animals we see today. Even though most groups are gone, their legacy lives on in us. The only living therapsids left on Earth are mammals.

Some fossils even show us clues about their skin. Some skin looked leathery and dimpled like an elephant's skin. Other clues suggest that some therapsids might have even had hair. This shows how slowly and surely animals change over millions of years. It is amazing to think that our own history started with these ancient creatures.

Therapsids are a major group of animals that include all living mammals and their ancestors. They belong to a larger group called synapsids. These creatures were once the most successful large animals on land. They first appeared more than 279.5 million years ago. They evolved from earlier synapsids known as pelycosaurs, specifically from a group called the Sphenacodontia.

By studying these fossils, scientists can trace the long history of how mammals eventually appeared.

One of the most important changes in therapsids was their physical structure. Many reptiles and pelycosaurs have a sprawling posture with legs sticking out to the sides. Therapsids developed limbs that were oriented more vertically underneath their bodies. This created a more "standing" quadrupedal posture. Their feet also became more symmetrical. The first and last toes were short, while the middle toes were long. This change allowed for a more mammal-like gait rather than a lizard-like crawl.

Their feeding tools also became much more advanced. The jaws of many therapsids grew more complex and powerful. Their teeth became specialized for different tasks, a process called differentiation. They had frontal incisors for nipping food. They had large lateral canines for puncturing and tearing meat. They also had molars for shearing and chopping.

This variety allowed different species to eat many different types of food.

Scientists are still learning about how therapsids managed their body heat. Many early Permian therapsids had a pineal foramen. This is a small hole in the skull for a parietal eye. This eye helped animals regulate temperature and biological rhythms. As therapsids evolved, many groups lost this hole. For example, probainognathian cynodonts lost the hole entirely. Some evidence suggests that endothermy, or the ability to maintain a constant body temperature, evolved in groups like dicynodonts and cynodonts near the end of the Permian.

Therapsids are divided into several major scientific groups or clades. These include the Biarmosuchia, the Dinocephalia, the Anomodontia, the Gorgonopsia, the Therocephalia, and the Cynodontia. The dinocephalians lived during the Middle Permian but died out later. The anomodont dicynodonts were very successful herbivores. The gorgonopsians were famous saber-toothed predators. The cynodonts are especially important because they gave rise to the Mammaliaformes. This happened in the Late Triassic around 225 million years ago.

History shows that therapsids faced many massive challenges. They were the dominant land animals from the Guadalupian through the Early Triassic. However, they were hit hard by the Permian–Triassic extinction event. Many successful groups, like the gorgonopsians, disappeared completely. During the Middle Triassic, they lost their dominance to the archosaurian sauropsids. These included dinosaurs and pterosaurs. Only the cynodont lineage truly survived the end of the Triassic. The Tritylodontidae, a family of very mammal-like cynodonts, survived even longer into the Early Cretaceous.

We can also find clues about what therapsid skin looked like. Most direct evidence of fur comes from docodonts, which are very close relatives of mammals. Some fossils of the dicynodont Lystrosaurus show skin that was leathery and dimpled, similar to an elephant. Other fossils, like the dinocephalian Estemmenosuchus, show skin that was glandular but lacked hair or scales. Some researchers believe hair may have first evolved in probainognathian cynodonts. This idea is supported by the way their skulls changed.

Today, mammals are the only living members of the therapsid lineage.