In so many features the Permian and Triassic periods differed from the present that if we could be transported back to that distant past, surely we would think that we were on another planet. The plants and animals would be largely unrecognizable – no mammals, and none of our modern trees or grasses. Although the nature and dispositions of the seas, lands, and mountains during that time are subject to different interpretations and conflicting views, who can doubt that the world's geography would be unrecognizable? The climate would have varied widely, from very cold at the beginning of the Permian (perhaps not unlike the glacial climate of the world a few thousand years ago) to a hot, dry climate during the Triassic, like nothing we see at present, followed by a warm climate continuing into the Jurassic.

Major changes in faunas were associated with the beginning of the Jurassic period, as reviewed by Boucot (1990), Dickins (1993a), and Hallam (1981). Boucot stated that “the modern marine … benthic fauna and communities really begin with the Jurassic.” In the latter part of the Permian and during the Triassic the earth was wracked by vast earthquakes, and great mountain chains were formed. There was magmatic-volcanic activity on an enormous scale. Some of those events are described in this volume, and some of the most interesting problems for future investigation are considered.