Therapsids Evolution

Introduction – Mammals are the dominant large unique group of animals having a number of morphological and physiological characteristics. They evolved from a group of reptiles called the synapsids. These reptiles arose during the Pennsylvanian Period (310 to 275 million years ago). A branch of the synapsids called the therapsids appeared by the middle of the Permian Period (275 to 225 million years ago). It was over millions of years that some of these therapsids evolved unique mammalian features that helped them to live in adverse environment situations.

Dentition(heterodont, thecodont and diphyodont)

2. Double occipital condyles

3. Double headed ribs

4. Well developed brain

5. Homeoiothermous (body temperature constant independent of environmental fluctuation)

6. Complete separation of oxygenated and deoxygenated blood

7.

*These small creatures, the so called mammals had efficient mechanism of regulating body temperature,well developed nervous system and efficient power of swift movement .*These features helped them to survive in the changing environment. *Thus mammals came into existence due to great climatic fluctuation from Permian to Jurassic (periodic aridity alternating with glacial periods). *Since mammal-like reptiles were abundant in Permian and in early Triassic period, they must have originated in late Permian or early