In geologic time, the Mesozoic Era, the second era in the Phanerozoic Eon, spans the time between roughly 250 million years ago (mya) and 65 mya.

The Mesozoic Era contains three geologic time periods including the Triassic Period (250 mya to approximately 206 mya), Jurassic Period (206 mya to approximately 144 mya), and the Cretaceous Period (144 mya to 65 mya).

The Mesozoic Era begins at the end of the Permian Period of the Paleozoic Era. The Mesozoic Era's Cretaceous Period ends with the K-T boundary or K-T event.

During the Mesozoic Era the Pangaean supercontinent spanned Earth's equatorial regions and separated the Panthalassic Ocean and the Tethys Ocean basins. At the start of the Mesozoic Era there was little differentiation or separation between the continental crust that would eventually form the North American, European, South American, and African Continents.

Driven by plate tectonics, by the middle of the Mesozoic Era (approximately 170 mya) the...