Interval of geologic time, 290–248 million years ago.
The last of the six periods of the Paleozoic Era , it follows the Carboniferous Period . During the Permian, the continents joined to form a single supercontinent, Pangea . Hot, dry conditions prevailed almost everywhere, and deserts were widespread. Life evolved as a continuation of established lines. Marine invertebrates evolved into several lineages. Marine and freshwater fish and amphibians thrived. Reptiles evolved into three distinct groups: the cotylosaurs, the pelycosaurs, and the therapsids. Land plants evolved from ferns and seed ferns to conifers and adapted to drier and well-drained land conditions. Toward the close of the Permian, many forms of life suffered mass extinction, whose causes are unknown.