Scincoidea

Evolutionary history: Scincoidea – the evolutionary radiation containing skinks and their closest relatives – is one of the ancient major lineages of squamate reptiles. Four living families belong to the clade: Scincidae, Cordylidae, Gerrhosauridae and Xantusiidae. Its evolutionary roots extend back into the Jurassic, while the principal living scincoidean lineages began diverging more than 130 million years ago. Their modern distribution is remarkably broad: skinks occur across much of the world, cordylids and gerrhosaurids are centred primarily in Africa and Madagascar, while xantusiid night lizards are native to the Americas.

Appearance and lifestyle: Scincoidea encompasses an extraordinary range of body forms. It includes sleek, smooth-scaled skinks as well as heavily armoured species protected by coarse scales and extensive dermal bone. These small bones, known as osteoderms, were probably already present in early scincoideans, remaining highly developed in several living lineages while apparently being secondarily lost in Xantusiidae. Limb reduction has evolved repeatedly, particularly among skinks, producing everything from conventional four-legged lizards to almost snake-like burrowers. Other members developed very different defensive solutions: when threatened, the South African armadillo girdled lizard (Ouroborus cataphractus) bites its own tail and curls into a ring, presenting its heavily spined armour to a predator.

Ecological role: Scincoideans occupy habitats ranging from leaf litter and loose soil to rocky mountainsides, forests and arboreal environments. Many prey on insects, arachnids and other small invertebrates, although omnivorous and partly herbivorous diets have also evolved. They are important consumers in terrestrial food webs while simultaneously providing prey for birds, snakes, mammals and other predators. Scincoidea currently contains close to two thousand recognised living species, the great majority of them skinks. Many species have extremely restricted ranges or depend on specialised island, mountain or rocky habitats, making habitat degradation, invasive species and unsustainable collection important conservation concerns for some lineages.