剑桥词典from or referring to the period of time between about 66 and 23 million years ago, in which many insects , mammals , and birds appeared 古第三纪的（迄今6600万至2300万年前） the Paleogene period 古第三纪 Paleogene flora and fauna 古第三纪动植物 the Paleogene noun [ 单数名词 ] the Paleogene period 古第三纪 返回 Paleogene