"If you're looking at this section, you may be a beginner without much previous knowledge. Of course, you may simply have been searching the web for an old
Nirvana CD and you ran across this page because, as it happens, you're also a moron. In either case, its unlikely that you have much background in Mesozoic zoology (or, for that matter, much taste in music). Accordingly, we'll keep this pretty basic and concentrate on the familiar
tetrapods.
The Mesozoic came after the
Paleozoic. The Paleozoic Era ended with the
Permian Period, which ended with a sort of general meltdown, sometimes called the "PT" or "End-Permian" extinction. We still aren't certain exactly what happened, but the fact that much of central Siberia turned into a sort of volcanic bubble bath for a few million years didn't help. This caused, bar none, the worst mass extinction in the last 600 My. Don't get this one confused with the "KT" extinction at the end of the Mesozoic -- the one which finished off the dinosaurs 200 My later. That was a sumo match by comparison. That is, it eliminated some very large and conspicuous folks very quickly, but it was all very quick and civilized."
http://www.palaeos.com/Mesozoic/Mesozoic.htm