The Triassic Period (from three-fold division in Germany) spanned the time from approximately 250 million years ago until 202 mya, and it begins the Mesozoic Era. Lifeforms in this time are significantly different to those that lived prior to the mass extinction at the end of the Permian.
In the oceans, the ammonoids were predominant survivors into the Mesozoic. On land, the thecodonts arose in the Early Triassic, eventually giving rise to the dinosaurs. Two other great groups appeared during this period; the birds and the mammals.
Classic Fossil-Bearing Sites
Moenkopi Formation, Arizona
Ischigualasto Badlands, Argentina
Newark Supergroup, eastern U.S.
Chinle Formation, Arizona
The Triassic Period began with the impact of the largest object ever to strike the Earth, and several other significant impacts occurred during the period. A 40 km craterform structure from about 250 million years ago is located in Brazil (and may be associated with the same fall that started the period.) A 23 km impact site from 225 mya is found in Manitoba, a 100 km structure (Manicouagan Lake) dated to 220 mya is found in Quebec, and a 215 million year old structure is located in the Ukraine.
Ninety-six percent of all species vanished at the end of the Permian. The subsequent opening of niches provided a wonderful opportunity for new lifeforms in the Triassic. During this period we see the rise of the thecodonts and their descendants, the dinosaurs and birds, and also the rise of mammals.
During the Permian all landmasses were congregated into a single equatorial supercontinent known as Pangaea.