These rudimentary eyes have a cornea, lens, and complex ciliary body, which allows them to detect light, but they are reduced in size and do not have an anterior chamber.

[6] Their name is derived from Amphisbaena, a mythical serpent with a head at each end—referencing both the manner in which their tail truncates, and their ability to move just as well in reverse as forwards.

A remnant of the pelvic girdle is present in all families, and Bipes and the genus Blanus have also retained a reduced femur.

[7] Amphisbaenians have a distinctive skin made up of rings of scales (annuli) that form a tube in which the loosely attached trunk of the body moves.

The presence of these reptiles is easily explained by the fact that they prey on the larvae of large beetles that also inhabit the leafcutter ants' galleries.

The specialized skull shape is hypothesized to be driven by environmental and ecological conditions, such as soil type, and is an instance of convergent evolution.

This hypothesis was supported by morphological data that dated amphisbaenian diversification to over 200 million years ago (Mya), while Pangaea was still intact.

[13] However, a recent study using a combination of molecular and fossil evidence suggests that amphisbaenians originated in North America, where they underwent their first divergence around 107 Mya.

This also implies that limblessness evolved independently three times, a finding that contrasts the morphological theory that limbed amphisbaenians are the most basal.

[14] The fully limbed Slavoia darevskii from the Late Cretaceous (Campanian) of Mongolia may represent an early relative of amphisbaenians.

[15] The oldest known modern amphisbaenians include members of Rhineuridae and the extinct family Oligodontosauridae from the Paleocene of North America.

[36] The following cladogram shows the relationships between the six amphisbaenian families determined in the phylogenetic analysis of mitochondrial and nuclear genes by Vidal et al.