Saturday, January 19, 2008

Skinny legs and all.

A different skink, Plestiodon egregius (Florida Mole Skink).

Referring to our friend Ablefaro, Pookie commented, "His footies seem so small in comparison to his bod. How do such little thangs manage to move him along fast enough to avoid predators?"

Part of the answer is that much of locomotion in lizards, especially high-speed locomotion, is accomplished by rapid lateral undulation of the body. In addition, as in all questions of function, size is important. Small-legged skinks are invariably small creatures, in the order of a few inches long and a few grams body weight. Relatively small legs provide enough force to move the body.

Hatchling Plestiodon egregius.

Interestingly, at birth (hatching) the limbs don't appear particularly small relative to the size of the body. But as the animal grows, the body increases in relative length, leading toward a primarily snake-like locomotory pattern. This can be advantageous in close quarters, among rocks, in loose soil beneath logs, or within sand, as is the case in the skink pictured here.

Another Florida Mole Skink.

Within sand, limbs of any size may even be counterproductive. This may be part of the story, in functional morphological evolutionary terms, of how to get from something similar to a Florida Mole Skink to something like Anniella pulchra.

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