Three thousand years ago,the northern distribution boundary of rhinoceros in China was more than 1,800km long from west to east along Yellow River.This is a fact few people know.During the recent three thousand years,the northern distribution boundary of rhinoceros in China expanded to move southward.It is an important feature of the regional extinction of rhinoceros population in China.The northern distribution boundary of rhinoceros shrank away southward at a surprising speed of about 0 5km per year.The ...