There are few known fossil specimens of these ancient snakes and only three in which the hind limbs are preserved and visible.
这些古老蛇类的化石标本非常稀少，仅有的三个标本的后肢保存完好并可见。
Most fossil specimens are little more than carbon impressions although distinctive shapes are known.
尽管清晰的形状已为人所知，但大多数化石标本只不过是炭质印痕。
There are few known fossil specimens of these ancient snakes, and only three in which the hind limbs are preserved and visible.
有关这些古老蛇类的化石标本非常稀少，仅有的三个标本的后肢是加工过并且可见的。
应用推荐