Physical characteristics

Uropeltids display a surprising diversity of external features despite their superficial resemblance. All are relatively small snakes, most having adult sizes below 12 in (30 cm) total length. A few species (e.g., Rhinophis oxyrhynchus, Uropeltis ocellatus) attain sizes nearly twice this length. In all uropeltids the eye is covered by an ocular shield with no separate spectacle. Instead, the region of the ocular shield overlying the eye is transparent. In species other than Platyplectrurus, the head tapers from a wider anterior trunk, and the snout is flattened either horizontally (dorsoventrally), as in Melanophid-ium and Platyplectrurus, or vertically (mediolaterally), as in most species of Rhinophis. Species with pointed snouts have modified rostral scales with thickened keratinized layers. In Rhinophis, one of the largest members of the family, the rostral scale is greatly enlarged and forms a prominent ridge over the dorsal surface of the snout. At the caudal end of these snakes, the tail has a variety of scale shapes, from pointed (Teretrurus sanguineus, Brachyophidium rhodogaster) to an obliquely flattened, very blunt end (most species of Rhinophis and Uropeltis). Uropeltids are designated "shieldtail" snakes because many species have a greatly enlarged terminal scale that has numerous spines or keels. The terminal scale in many is preceded by a region of thickened, keeled scales that form an oval, obliquely flattened surface. The keels and spines on these scales become encrusted with soil particles and, in wet soils, an appreciable plug of soil several millimeters thick may tightly adhere to the modified scales of the tail tip. Carl Gans has suggested that the soil plug may serve in defense against some types of burrowing predators.

Uropeltid skin colors vary from browns, grays, and black, often with light yellow or white scale edges on the ventral surface (many species), to dark, iridescent blue dorsally and a bright yellow with darker spots ventrally (Uropeltis myhendrae). A number of species are brown with dark bands rising from the

A large-scaled shieldtail (Uropeltis macrolepis macrolepis). Photo by A. Captain/R. Kulkarni/S. Thakur. Reproduced by permission.

ventral surface and appear superficially similar to some species of large centipedes. Gans suggested that some Sri Lankan species may mimic small snakes of the family Elapidae, and tests with domestic chickens suggested that some ground-feeding birds, like jungle fowl, may avoid exposed uropeltids.

Among the more unusual features of uropeltids is the modification of their trunk musculature into an anterior region of red fibers rich in myoglobin and mitochondria, whereas the remainder of the trunk muscles are white. These snakes burrow by forcing their heads through the soil, anchoring the anterior trunk with tight bends of the vertebral column, then straightening the trunk anterior to these bends. Much of the work during burrowing is thus apparently done by the anterior trunk and its fatigue-resistant red muscles.

Although uropeltids retain many primitive features in skeletal and muscle arrangements, they have no pelvic vestiges, no premaxillary teeth, and reduced left lungs. Among uropeltid genera considered derived for the group (Rhinophis and Uropeltis), the maxilla is firmly anchored to the premax-illa, and many of the bones at the rear of the skull are fused. In more basal uropeltids, the maxilla is free of the premaxilla, and there is less fusion of skull elements.

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