七鳃鳗是地球上最早期的脊椎动物——无颌类的一种极度特化了的孑遗。七鳃鳗的样子很像一般的鳗鱼,身体细长,表皮裸露无鳞,背上有一条长长的背鳍,向后一直延伸到尾端并环绕尾部形成尾鳍,这是首次发现于中生代地层中,首次发现于欧亚大陆上,首次发现于淡水环境里。与美国发现的石 The Lamprey is the earliest vertebrate on earth - an extremely specialized relic of a jaw-free species. The lamprey looks like an ordinary eel. It is slender in body and has an uncultivated epidermis. The back has a long dorsal fin extending back to the tail and caudal fin around the tail, which was first discovered in the Mesozoic strata , First discovered in Eurasia, first discovered in freshwater environment. Stone found with the United States