The Mesozoic Era lasted approximately 185.5 million years; it began around 251 million years ago with the Triassic Period, and it remained until 65.5 million years ago with the end of the Cretaceous Period. read more
The Mesozoic (literally "middle life") Era lasted from around 252.2 million years ago to around 66.0 million years ago: i.e. for approximately 186.2 million years. read more