Blindskinks (Dibamidae)

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Blindskinks

(Dibamidae)

Class Reptilia

Order Squamata

Family Dibamidae

Thumbnail description
Small, secretive brown fossorial lizards with blunt heads and tails

Size
Small to medium-sized lizards, about 2–10 in (50–250 mm) in snout-vent length

Number of genera, species
2 genera; 11 species

Habitat
Forests, rainforests, semi-arid deciduous brush, semi-arid open scrubland, dense bush, deciduous scrub, dense forest, and pine-oak forest

Conservation status
Not threatened

Distribution
Disjunct: northeastern Mexico and Southeast Asia

Evolution and systematics

Exact affinities of these small, wormlike, burrowing scleroglossans remain unknown. They could be related to other fossorial scincomorphans, amphisbaenians, or even to snakes. Many of the traits they share with other squamate groups could have evolved convergently, however, in response to their subterranean habits. Although the geographic distributions of the two genera of dibamids are widely separated, their relationship to each other is supported strongly by numerous shared derived characteristics, some of which also are shared with members of various other lizard families. Dibamids have diverged greatly from other squamates and could represent remnants of an extremely ancient lineage. No subfamilies are recognized.

Physical characteristics

Blindskinks are small to medium-sized lizards, about 2–10 in (50–250 mm) in snout-vent length. They are brown, with short, blunt tails, which break at fracture planes in tail vertebra. Forelimbs and bones of the pectoral girdle are entirely absent. Males have small flaplike hind limbs somewhat reminiscent of those of some pygopodids, perhaps used in courtship or copulation. Females are entirely limbless. Remnants of the pelvic girdle are present. Dibamus are the only squamates with pores on their lower legs. As in many burrowers, the skulls consist of massively fused bones, parts of which have lost the ability to move with respect to one another. The heads are blunt, and eyes are vestigial and lie beneath an immovable head scale. Paired frontal and nasal bones and scales are present. The parietal bone is fused, without a foramen. Teeth are pleurodont, set in sockets, and small, and they curve backward to a single point. There are no teeth on the palatal or pterygoid bones. Tongues are covered dorsally with filamentous papillae, without lingual scales. The fore-tongue is nonretractable. The nostrils are located at the tip of the snout on an enlarged rostral scale. They have no external ear openings. Their bodies are covered with shiny, smooth, overlapping scales without osteoderms.

Distribution

Commonly known as blindskinks, only two genera of dibamids exist. The single species of Anelytropsis lives in a tiny area in northeastern Mexico. (Only 19 specimens had been collected by 1985.) The 10 species of Dibamus are scattered around Southeast Asia, from the Nicobar Islands across the islands of the Indo-Australian archipelago, including the Sunda Islands. They also occur in Vietnam, southern Thailand, Malaysia, Sumatra, most of Indonesia, Borneo, the Philippines, and westernmost New Guinea (Irian Jaya).

Habitat

Dibamus requires humus in moist condition, burrowing deep beneath rocks or logs during dry seasons. Anelytropsis is adapted to a wider variety of drier habitats, including semiarid deciduous brush, semi-arid open scrubland, dense bush, deciduous scrub, dense forest, and pine-oak forest. Anelytropsis has been found beneath rocks, in or under rotting logs, in the decayed bases of yuccas, and in loose litter.

Behavior

Dibamids are secretive, living on the forest floor, often underneath stones but sometimes underneath leaf litter, or moving about underground, sometimes inhabiting burrows and crevices or the catacombs of social insect nests. They exploit existing burrows and openings in the soil but can burrow in loose, friable soils or decomposing leaf litter.

Feeding ecology and diet

Like most lizards, they are thought to eat insects.

Reproductive biology

Dibamus lays a clutch of just a single egg but may deposit several clutches during a season. Dibamus eggs are soft and elongated when laid, but they become more spherical and calcify and harden after deposition. Nothing is known about reproduction in Anelytropsis.

Conservation status

Not threatened; although many species are susceptible to habitat loss. There are currently no conservation efforts underway to protect dibamids.

Significance to humans

None known

Resources

Books

Estes, R., K. de Queiroz, and J. Gauthier. "Phylogenetic Relationships Within Squamata." In Phylogenetic Relationships of the Lizard Families, edited by R. Estes and G. Pregill. Stanford, CA: Stanford University Press, 1988.

Pianka, E. R., and L. J. Vitt. Lizards: Windows to the Evolution of Diversity. Berkeley: University of California Press, 2003.

Pough, F. Harvey, Robin M. Andrews, John E. Cadle, Martha L. Crump, Alan H. Savitzky, and Kentwood D. Wells. Herpetology. Upper Saddle River, NJ: Prentice Hall, 1998.

Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd edition. San Diego: Academic Press, 2001.