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 古第三紀的（迄今6600萬至2300萬年前） the Paleogene period 古第三紀 Paleogene flora and fauna 古第三紀動植物 the Paleogene noun [ 單數名詞 ] the Paleogene period 古第三紀 返回 Paleogene