Lizards of glass - Reptilenesia
I love snakes, but I am also partial to other limbless animals, especially limbless vertebrates. Among the salamanders, sirens and amphiumas are some of my favorites. Caecilians are also pretty cool. And in the sister group to the snakes, it’s hard to pass up the many species of legless lizard. Snakes are pretty much just legless lizards too since they evolved from lizard ancestors, but they have undergone spectacular evolutionary radiation into over 3,000 species in over 20 families. Elsewhere in the lizard family tree, limblessness has evolved many times, usually in concordance with a fossorial or burrowing habit.
The southeastern US is home to four species of legless lizard, called glass lizards, in the genus Ophisaurus, which means snake-lizard (ophi for a snake, and saurus for a lizard, as in dinosaur). They are not closely related to snakes, nor to any other species of southeastern lizard, but rather to the alligator lizards of the pacific northwest, genus Elgaria. They can be differentiated from snakes by several characteristics. Chief among these are the presence of external ear openings and of moveable eyelids, both of which snakes lack. Instead, the eyes of snakes are covered by a hard, clear scale known as a spectacle. Snakes cannot hear, although they are very sensitive to vibrations of the ground and air, so they can detect most airborne sounds almost as if they are feeling them. Our sense of hearing (and the glass lizards’) is a mechanical sense also, so it’s not really that different.
In addition to these subtle features, the glass lizards possess a longitudinal groove that runs down each side of their body, which snakes lack. This groove allows the body wall to expand and contract as they breathe, digest food, and reproduce. Snakes have solved this problem in two different ways. One is to reduce or stagger the internal organs so that they fit better into a cylindrical body. Many of the paired organs, such as kidneys and gonads, are situated one in front of the other, and some are no longer paired, such as the single left lung. Snakes also have extremely stretchy skin that allows considerable distortion of the body after they have eaten a large prey item, but glass lizards have two lungs and are quite rigid. You can feel the stiffness of a glass lizard when you pick it up – but when you do, be careful! They aren’t called glass lizards for nothing. Like many lizards, glass lizards can break off, or autotomize, their tails, which can serve to distract a predator in pursuit, which may choose to attack the writhing tail while the body slinks away inconspicuously. In some glass lizards, the tail may be as long as or longer than the body, so the effect can be quite dramatic.
