Evolution and systematics

Most recent phylogenetic analyses have placed amphisbae-nians as one of three suborders of Squamates (the clade that includes snakes, lizards, and amphisbaenians), but their exact placement within that clade is not well understood. The interrelationships among the four amphisbaenian families are also poorly understood. On the one hand, the retention of fore-limbs in bipedids, in contrast to the completely limbless condition in all other amphisbaenians, suggests that those forms may be the most primitive amphisbaenians. On the other hand, the only amphisbaenian family with a good fossil record is the Rhineuridae, and some of those fossil forms, although limbless, retain different primitive features, such as fully formed, enclosed orbits, suggestive of a potentially basal position for this group within amphisbaenians. Unfortunately, bipedids have no fossil record at all. No subfamilies are recognized.

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