Rhaetian Stage

Fourth Mass Extinction of Animals

The Rhaetian (209–201 Ma) is the last age of the Late Triassic and the Triassic Period, occurring after the Norian, and before the Jurassic Period.

There was a extinction event at the end of the Triassic which killed of the large thecodonts and allowed dinosaurs to rule as the single large terrestrial animal clade throughout the Mesozoic.
While the Manicouagan in northeastern Canada is usually cited as the impact crater in this instance, it is now considered a little too early in age, and the Triassic/Jurassic (and for that matter the Jurassic/Cretaceous) boundary appears to involve multiple impacts

Oxygen-depleted toxic oceans had key role in mass extinction over 200 million years ago (Univ. of Southampton)
Rhaetian Stage (Palaeos web page)