一、引言扬子鳄,中国古籍称鼍,为现今全世界二十多种鳄类之一,是我国所特有而数量极少的一种珍贵动物,也是国际上交换的佳礼。它的形态和生活习性,前人巳有论述。但近六、七千年来它在地理分布上的变迁及其原因,却还没有研究,也不够清楚。我们 I. Introduction The alligator, known as the ancient Chinese book, is one of the more than twenty kinds of crocodilians in the world today. It is a rare and rare animal of our country and an exchanging gift for the international community. Its form and living habits are not discussed by previous generations. However, its geographical distribution and its causes in the past six or seven thousand years have not yet been studied and are not clear enough. we