Bipedidae

Bipedidae is a small family of amphisbaenian lizards, commonly known as two-legged worm lizards. Members of this group are characterized by having two forelimbs and no hind limbs, a body adapted for a fossorial, or burrowing, lifestyle. They possess an elongated, segmented body with reduced eyesight, and their scales often form a protective, wheel-like pattern that assists movement through soil.

The family comprises two genera, Bipes and Anelytropsis, with several described species. Bipedids are native to the Americas, primarily in western Mexico, where they inhabit deserts, scrublands, and loose soil under leaf litter, rocks, or within termite nests. They are elusive and rarely seen due to their subterranean habits.

Anatomically, the retention of forelimbs alongside the loss of hind limbs distinguishes bipedids from other amphisbaenians. This limb configuration is a distinctive adaptation within a lineage that is otherwise dorsoventrally flattened and highly specialized for burrowing. The exact functional role of the forelimbs in locomotion and digging has been a subject of study, but their presence marks a notable deviation within the broader amphisbaenian radiation.

Ecology and diet center on a fossorial existence. Bipedids feed on small invertebrates, including termites, ants, and earthworms, and they spend most of their lives underground. Reproduction varies by species, with some laying eggs and others bearing live young. Due to their restricted ranges and specialized habitats, certain species are of conservation concern, and data on their distribution and biology remain limited.