The Permian Triassic boundary (PTB) is marked by the largest extinction event ever recorded in Earth’s history and the longest recovery period of the Phanerazoic. So great was the subsequent change in life-forms existent on the planet after the PTB that we refer to this boundary as the end of the Paleozoic and the beginning of the Mesozoic, the Era of “middle life”. The cause of this great extinction has been widely debated since its discovery.

During the advent of the Triassic, marine biotas were seriously impoverished; 90% of all marine life had been eradicated. Many species of brachiopods, corals, mollusks and other marine invertebrates had totally disappeared. Strophomenid Brachiopods, Trilobites, Blastoids and many types of Crinoids were gone forever; re-radiation after the end of the Permian would be very slow for those groups that remained. Following the extinction of many Paleozoic faunas, hard-shelled invertebrates would come to constitute the modern evolutionary fauna and include gastropods, bivalves, ammonoids, echinoids and some brachiopods. (Jin, 2000) Additionally, many surviving taxa were geographically or otherwise isolated, slowing their re-emergence until the middle to late Triassic. (Chen, 2005)