Therapsida

Therapsida is a major group of synapsids, and includes mammals and their ancestors. They are characterized by their advanced jaw structure and differentiated teeth. Therapsids were the dominant terrestrial vertebrates during the Permian period and continued to be significant during the Triassic period.

Evolution and Classification

Therapsids evolved from a group of synapsids known as pelycosaurs during the middle Permian period. They are divided into several subgroups, including Anomodontia, Gorgonopsia, Therocephalia, and Cynodontia. The latter group, Cynodontia, is particularly important as it includes the direct ancestors of mammals.

Anomodontia

Anomodonts were primarily herbivorous therapsids. The most well-known anomodonts are the Dicynodonts, which had beak-like mouths and tusks.

Gorgonopsia

Gorgonopsians were predatory therapsids with long canine teeth. They were among the top predators of the late Permian period.

Therocephalia

Therocephalians were a diverse group of therapsids that included both carnivorous and herbivorous species. They are known for their advanced cranial features.

Cynodontia

Cynodonts are the most mammal-like of the therapsids. They had differentiated teeth and a more advanced jaw structure. This group includes the ancestors of modern mammals.

Anatomy

Therapsids exhibit several advanced features compared to their pelycosaur ancestors. These include a more upright posture, a secondary palate, and differentiated teeth (incisors, canines, and molars). Their jaw structure is more complex, allowing for more efficient food processing.

Fossil Record

Therapsid fossils have been found on every continent, indicating they were widespread during their time. Significant fossil sites include the Karoo Basin in South Africa, which has provided a wealth of information on Permian and Triassic therapsids.

Extinction and Legacy

Many therapsid groups went extinct during the Permian-Triassic extinction event, but some lineages, particularly the cynodonts, survived and continued to evolve into the first mammals during the late Triassic period.

See Also

• Synapsid
• Mammal
• Permian period
• Triassic period
• Pelycosaur