Mesozoic (adj.)

in geology, "of or found in that part of the geological series between the Paleozoic and what was then called the Tertiary," 1840, from Greek mesos "middle" (from PIE root *medhyo- "middle") + zoe "life" (from PIE root *gwei- "to live") + -ic. The name was coined by British geologist John Phillips for the fossil era "between" the Paleozoic and what is now the Cenozoic. An older name for it was Secondary.