from or referring to the period of time between about 250 to 65 million years ago

The Cretaceous was the last of the Mesozoic periods and had the most dramatic and varied life forms. 白垩纪是中生代的最后一个时期，有最为特別和多样的生命形式。

In 1967 he described a fossil ant of the Mesozoic Age. 他在1967年描述了一块中生代的蚂蚁化石。

the period of time between about 250 to 65 million years ago

There were three periods in the Mesozoic - the Triassic, Jurassic, and Cretaceous periods. 中生代分为三个时期——三叠纪、侏罗纪和白垩纪。

The fossil evidence seems to support the theory that mammals began to exceed reptiles during the Mesozoic. 化石证据似乎支持哺乳动物的数量在中生代开始超过爬行动物的理论。