The Permian period was, literally, a time of beginnings and endings. It was during the Permian that the therapsids, or "mammal-like reptiles," first appeared--and a branch of therapsids spawned the very first mammals of the ensuing Triassic period. However, the end of the Permian witnessed the most severe mass extinction of life in the history of the planet, even worse than the one that doomed the dinosaurs tens of millions of years later. The Permian was the last period of the Paleozoic Era (542-250 million years ago), preceded by the Cambrian, Ordovician, Silurian, Devonian and Carboniferous periods.
Climate and geography. As during the preceding Carboniferous period, the climate of the Permian period was intimately linked with its geography. Most of the earth's land mass remained locked up in the huge supercontinent of Pangea, with remote offshoots comprising present-day Siberia, Australia and China. During the early Permian period, large portions of southern Pangea were covered by glaciers, but conditions warmed considerably by the beginning of the Triassic period, with the reappearance of vast rain forests at or near the equator. Ecosystems around the globe also became considerably drier, which spurred the evolution of new types of reptiles better adapted to cope with the arid climate.
Terrestrial Life During the Permian Period
Reptiles. The most important event of the Permian period was the rise of "synapsid" reptiles (an anatomical term denoting the existence of one hole in the skull behind each eye). During the early Permian, these synapsids resembled crocodiles and even dinosaurs, as witness famous examples like Varanops and Dimetrodon. By the end of the Permian, though, the synapsids had branched off into the therapsids, or "mammal-like reptiles"; at the same time, the very first archosaurs appeared, diapsid reptiles characterized by the two holes in their skulls behind each eye. A quarter of a billion years ago, no one would have guessed that these archosaurs were destined to evolve into the first dinosaurs of the Mesozoic Era!
Amphibians. The increasingly dry conditions of the Permian period were not kind to amphibians, which found themselves out-competed by more adaptable reptiles (which could venture further onto dry land to lay their eggs). Two of the most notable amphibians of the early Permian were the six-foot-long Eryops and the bizarre Diplocaulus, which looked like a tentacled boomerang.
Insects. During the Permian period, the time wasn't yet ripe for the explosion of insect forms seen during the Mesozoic Era. The most common insects were giant cockroaches, the tough exoskeletons of which gave them a selective advantage over other terrestrial invertebrates, as well as various types of dragonfly, which weren't quite as impressive as their plus-sized forebears of the earlier Carboniferous period, like Megalneura.
Marine Life During the Permian Period
The Permian period has yielded surprisingly few fossils of marine vertebrates; the best-attested genera are prehistoric sharks like Helicoprion and Xenacanthus and prehistoric fish like Acanthodes. Marine reptiles were extremely scarce, especially compared to their profusion in the ensuing Triassic period; one of the few known species is the mysterious Claudiosaurus.
Plant Life During the Permian Period
If you're not a paleo-botanist, you may or may not be interested in the replacement of one weird variety of prehistoric plants (the lycopods) by another weird variety of prehistoric plants (the glossopterids). Suffice it to say that the Permian witnessed the evolution of new varieties of seed plants, as well as the spread of ferns, conifers and cycads (which were an important source of food to the reptiles of the Mesozoic Era).
The Permian-Triassic Extinction
Everyone knows about the K/T Extinction that wiped out the dinosaurs 65 million years ago, but the most severe extinction event in earth's history was the one that transpired at the end of the Permian period, which wiped out 70 percent of terrestrial genera and a whopping 95 percent of marine genera. No one knows exactly what caused the Permian-Triassic Extinction, though a series of massive volcanic eruptions is the most likely culprit. It was this "great dying" at the end of the Permian that opened up the earth's ecosystems to new kinds of terrestrial and marine reptiles, and led, in turn, to the eventual evolution of dinosaurs.
Next: the Triassic Period