Reptiles
Fringe-toed Lizard
Uma · also called fringe-toed lizards, sand lizards
A fringe-toed lizard treats loose desert sand the way a fish treats water: sprinting across it on toes fringed with comb-like scales that work like built-in snowshoes, then diving straight in and vanishing beneath the surface the instant a predator gets too close. Sealed nostrils and a wedge-shaped jaw keep sand out of everything that matters while it disappears.
Overview
Fringe-toed lizards, genus Uma, are highly specialised desert reptiles of active, wind-blown sand dunes in the southwestern United States and northern Mexico. Rows of flattened scales on each toe act like snowshoes, giving them exceptional speed and traction on loose sand that leaves most animals struggling.
Built for sand, and only sand
Valve-like nostrils, a countersunk jaw, and adapted eyelids let the lizard dive headfirst into sand and briefly “swim” beneath it to escape danger. This extreme specialisation is also its biggest vulnerability — the lizard has little ability to survive in nearby rocky or firmer desert habitat if its specific dune system is disturbed.
Status
Vulnerable and decreasing — active sand dunes have been fragmented by development, off-road vehicles, and invasive vegetation stabilising the dunes the species depends on entirely.
Fringe-toed Lizard: common questions
How do the fringes on a fringe-toed lizard's feet actually help it move?
The rows of flattened, projecting scales along each toe significantly increase the surface area of the foot in contact with loose sand, functioning similarly to a snowshoe by distributing the lizard's weight over a larger area and preventing the foot from sinking into the sand with each step. This adaptation gives the lizard considerably better traction and allows for much faster, more efficient movement across loose dune surfaces than a foot without this fringed structure could achieve.
How does a fringe-toed lizard avoid getting sand in its eyes, ears, and nose while burrowing?
The species has a number of specialised adaptations for this exact purpose, including valve-like flaps that can close over the nostrils to keep sand out of the airway, a wedge-shaped, countersunk lower jaw that helps it push through sand smoothly, and eyelid and ear structures adapted to minimise sand intrusion during rapid burrowing or diving into the sand. Together these adaptations allow the lizard to move through and beneath loose sand quickly and repeatedly without being significantly hindered or injured by sand exposure.
Why can't a fringe-toed lizard just move to a different type of desert habitat if its sand dunes are disturbed?
Its most distinctive physical adaptations, including the fringed toes and specialised sand-diving and sand-burrowing anatomy, are specifically suited to loose, fine, wind-blown sand and offer little or no advantage on firmer, rockier, or more vegetated desert ground, meaning the lizard is poorly equipped to compete, forage, or escape predators effectively in a different habitat type. This tight specialisation is exactly why active sand dune habitat loss has such a disproportionately serious impact on fringe-toed lizard populations compared with more habitat-generalist desert reptile species.
What does a fringe-toed lizard do when a predator approaches?
In addition to relying on considerable speed across open sand, a fringe-toed lizard's most distinctive escape behaviour is diving directly into loose sand and effectively swimming a short distance beneath the surface, disappearing from a predator's view almost instantly. This sand-diving escape, supported by its specialised jaw shape and sand-excluding nostril and eye adaptations, is a highly effective way to vanish quickly in open dune habitat that otherwise offers very little other cover to hide in.