Reptiles
The beginning of the age of reptiles, since the middle of the continent of pangaea was desert and the northern part was dense and humid that was their main habitat since they can withstand the heat from their tough moisture retaining skin and so thrived more than most of the other animal types. Since the reptiles were cold-blooded some adapted to the continually changing temperatures by forming heat exchangers such as the sail like muscle on the reptile in the picture which meant they absorbed the heat through that sail and when it became night the sail would give the reptile heat. They were mainly predators, eating any poor thing that got in their line of sight and had the jaws and teeth to do so along with agility.
Therapsids
The evolution of the reptiles forming the warm blooded animals and later the birth of mammals. Since this reptile was warm blooded it needed energy to keep its warmth and to get energy meant to feed, these were the dominant land animals at the time until the reptiles grew in size at the end of this period. These therapsids grew in size as well and became ferocious fanged predators or big herbivores, later in the period smaller variants of these animals were produced and began growing hair, and that is when the mammals started to come into the later periods.
Marine life
The Marine life wasn't what any animal wanted to be at the end of the permian period, 90% of the marine life went extinct as well as 70% of land animal life, no one knows why though although there are theories of methane gas being released, or volcanic eruptions causing debris into the atmosphere and blocking out the sun. The marine life of the permian period was mainly mollusks as well as bony fish, but by the time of the drastic climate change and the inconsistency of it most life died off and became extinct.