from 63 million to 58 million years ago; appearance of birds and earliest mammals
双语例句
Paleontological studies showed that modern avian groups probably first appeared in the Paleocene and experienced an explosive radiation in the early Cenozoic. 古生物学研究表明，现生鸟类的最早出现是在古新世，而爆发性辐射演化发生在新生代早期。
