The Uropeltidae, the shieldtail or shield-tailed snakes, are a family of primitive, nonvenomous, burrowing snakes endemic to peninsular India and Sri Lanka. The name is derived from the Greek wordsura and pelte, indicating the presence of the large keratinous shield at the tip of the tail. Seven or eight genera are recognized, depending on whether Teretrurus rhodogaster is treated in its own genus or as part of Brachyophidium. The family comprises over 50 species. These snakes are not well known in terms of their diversity, biology, and natural history.
Description
These are small snakes, with adults growing to between 20 and 75 cm in length. They are adapted to a fossorialway of life, which is apparent in their anatomy. The skull is primitive and inflexible, with a short, verticalquadrate bone and rigid jaws; the coronoid bone is still present in the lower jaw. The orbital bones are absent, the supratemporal is vestigial and the eyes are small and degenerate, not covered by a brille, but by large polygonal shields. However, the pelvis and hind limbs, the presence of which is also considered a primitive trait, have disappeared in this family. The tail is characteristic, ending in either an enlarged rigid scale with two points, or more often an upper surface with a subcircular area covered with thickened spiny scales, or a much enlarged spiny plate. The ventral scales are much reduced in size. The body is cylindrical and covered with smooth scales.
Behaviour and natural history
Many species of shieldtail snakes are rather poorly known in terms of natural history. Field studies indicate that most species are obligate burrowers and may often come out on to soil surface during rainy nights. Even roadkills of these snakes have been recorded by field biologists during peak monsoon rains. They seem to prefer the humus-rich topsoil layers and rarely burrow deeper inside. When approached by predators, these snakes do not bite like most snakes, but coil their bodies into a ball and hide their heads tucked underneath. Some may poke with their harmless tail tip, like a worm snake. Many have a drab and dull-coloured back, but a very bright, contrastingly coloured underside to startle predators by turning upside down and twitching. This aposematic colouration wards off would-be predators.
Because of their peculiar geographic distribution, with many hill ranges in South India and Sri Lanka having an endemic shieldtail, they are thought to be analogous to Darwin's finches, in a broader sense - an evolutionary radiation. This is the only family of snakes endemic to South Asia. Genetic studies on this group have brought forth largely similar results as regards common ancestry and phenotypic diversification patterns. Molecular dating analysis has suggested that uropeltids originated around the Paleocene - Eocene boundary splitting from its sister cladeCylindrophiidae + Anomochilidae around 56 MYA.
Feeding
Their diets consist mostly of invertebrates, particularly earthworms, and many species have actually been observed in the wild by researchers to eat earthworms. Frank Wall, who dissected many species for analysing the gut contents to study the diet, remarks about the presence of worms and mud.
Reproduction
All members of this family retain eggs that hatch within the body of the mother.
