11 February 2021

The worm lizard that’s rather like a whale

May I introduce Bipes biporus, also known as the Mexican mole lizard or Belding’s mole lizard.

Mexican worm lizard (Bipes biporus).

It’s an odd and fascinating beast, because it has arms (forelimbs) but no legs (hindlimbs). You can see its front legs very well in the picture above. They even look pretty chunky relative to the head.

Head and forelimbs of Mexican worm lizard (Bipes biporus).

But there are no obvious rear legs.

Mexican worm lizard (Bipes biporus).

There are tiny remnants of leg bones in the back of the animal, but they are not visible just by looking at the animal.

Pelvic skeleton from Mexican worm lizard (Bipes biporus).

Above is Figure 8 from Zangerl (1945).

A more recent paper (Kearney and Stuart 2004) says Blanus (another worm lizard genus) has forelimb skeletal elements but only vestiges of rear limbs. But pictures of Blanus don’t show obvious limbs like Bipes does.

Why do I say this worm lizard is like a whale? Because like whales, only the forelimbs are visible. The hindlimbs are all but lost. In some ways, the worm lizard is a more impressive specimen of evolution because its forelimbs are still obviously arms, unlike the flipper of a whale, which is so heavily modified that its relationship to out own arms is obscured.


Kearney M,  Stuart BL. 2004. Repeated evolution of limblessness and digging heads in worm lizards revealed by DNA from old bones. Proc. R. Soc. Lond. B. 271: 1677–1683. http://doi.org/10.1098/rspb.2004.2771

Zangerl R. 1945. Contributions to the Osteology of the Post-Cranial Skeleton of the Amphisbaenidae. American Midland Naturalist 33: 764–780.

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