252-66 Million Years Ago
The Mesozoic Era began after the end of the Permian extinction, when 96% of species were vanquished, including trilobites. Known as the age of reptiles, the Mesozoic Era gave rise to dinosaurs and flowering plants. For more than 186 million years, dinosaurs grew in size, ruling land and sea until their own demise 66 million years ago, when their environment was shattered by a cosmic impact. Mesozoic geologic strata are almost entirely missing from Illinois; while no dinosaur fossils have been found, paleontologists remain hopeful about the scant Cretaceous strata in southernmost Illinois. We can reconstruct Mesozoic flora and fauna based on fossils in nearby states. The three periods of the Mesozoic Era are the Triassic, the Jurassic, and the Cretaceous.