The Middle Triassic is the second of three epochs of the Triassic period. It lasted from about 247.2 million years ago (mya) to ~237 mya.
Once the middle series in the Triassic was known as the Muschelkalk. This name is now only used for a unit of rock strata of Middle Triassic age, found in western Europe.
Archosaurs were initially rarer than the therapsids which had dominated Permian terrestrial ecosystems, but they began to displace therapsids in the Middle Triassic. This 'Triassic takeover' may have contributed to the evolution of mammals. It forced the surviving therapsids and their mammalian successors to live as small, mainly nocturnal insectivores. Nocturnal life probably forced the proto-mammals to develop fur and higher metabolic rates. In their burrows, keeping warm, looking after the young and feeding them with milk were keys to their later success.
The ancestors of crocodiles, and the ancestors of pterosaurs and dinosaurs, were the most important archosaurs of this epoch.
In the Tethys Ocean, the first sauropterygia were present, the nothosaurs and early plesiosaurs. Ichthyosaurs had arrived in the Lower Triassic.