For mammals like echidnas and kangaroos, the water proved too great a hurdle.

对于和袋鼠这样的乳动物来说，海水是一个非常大的障碍。

Only two kinds of mammals, the platypus and the echidna, lay eggs.

只有两乳动物，也就是鸭嘴兽和鼠会产蛋。

There were once hundreds of monotreme species, but there are only five left: four species of echidnas and the duck-billed platypus.

曾经有好几百单孔目乳动物，现在仅存5：4和鸭嘴兽。

Back on the road It didn't take long until we ran into one of Australia's weirdest animals: the echidna.

返回路上 没过多久，我们就遇到了澳大利亚最奇怪的动物之一：。