relating to or denoting the era between the Palaeozoic and Cenozoic eras, comprising the Triassic, Jurassic, and Cretaceous periods

fossils of Mesozoic birds have been described at an unprecedented rate

the era between the Palaeozoic and Cenozoic eras or the system of rocks deposited during it

the history of mammals extends back to the early part of the Mesozoic