Amphisbaenia
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Amphisbaenidae |
Amphisbaenia is a subgroup (suborder or infraorder) of the reptile order Squamata composed of peculiar, usually small and legless animals, known as worm lizards.
Extant (living) reptiles (Class Reptilia) are generally placed into four orders: Testudines (turtles), Rhynchocephalia (tuatara), Crocodilia (crocodilians) and Squamata (lizards, snakes, and worm lizards). Thus, worm lizards are distantly related to lizards and snakes, in spite of their resemblance to worms (due to their pink color and scales arranged in rings).
Although reptiles are tetrapods, meaning they are "four-legged" vertebrates, and worm lizards are usually legless, they are still considered tetrapods because it is assumed that they evolved from forms that did have appendages. The extraordinary diversity of nature complicates classification based on anatomical features; in general, taxonomy seeks for relationships based on common lineage.
Worm lizards are very poorly known, due to their burrowing lifestyle and general rarity. Only two species are known to exist in the United States, with most worm lizards being in Africa and South America.
Characteristics
Little is known of worm lizards outside of their anatomy, and even that is difficult to study due to the mechanics of dissecting something so small (most species are less than six inches long).
The head is stout, not set off from the neck, and either rounded, sloped, or sloped with a ridge down the middle. Most of the skull is solid bone, and they have a distinctive single median tooth in the upper jaw. They have no outer ears, and the eyes are deeply recessed and covered with skin and scales. The body is elongated, and the tail truncates in a manner that vaguely resembles the head. Their name is derived from Amphisbaena, a mythical serpent with a head at each end.
The skin of amphisbaenians is only loosely attached to the body, and they move using an accordion-like motion, in which the skin moves and the body seemingly just drags along behind it. Uniquely, they are also able to perform this motion in reverse, just as effectively.
Distribution
Amphisbaenians are found in North America, Europe, Africa, South America, the Middle East, and the Caribbean, a surprisingly large distribution despite being small subterranean animals that rarely ever leave their burrows. A study using a combination of molecular and fossil evidence suggests that amphisbaenians originated in North America, where they underwent their first divergence around 107 Mya (Longrich, et al. 2015). They then underwent another major diversification into North American and European forms 40–56 Mya. Finally, the African and South American forms split around 40 Mya. This suggests that worm-lizards crossed the Atlantic Ocean (which had fully formed by 100 Mya) twice, once just after the K–Pg extinction, and then again, later in the Palaeogene. This also implies that limblessness evolved independently three times, a finding that contrasts the morphological theory that limbed amphisbaenians are the most basal. This widespread dispersal is suggested to have occurred by rafting – natural erosion or a storm event loosened a large raft of soil and vegetation that drifted across the ocean until landing on another shore. This oceanic rafting would be feasible due to the subterranean lifestyle and small nutritional requirements of amphisbaenids. After the Chicxulub impact, many predators of amphisbaenians became extinct, which allowed colonist amphisbaenians to thrive in new territories (Longrich, et al. 2015).
Classification
Benton (2024) considers Amphisbaenia to be an infraorder within the Squamata Order, while considering the lizards (Lacertilia or Sauria) and snakes (Serpentes or Ophidia) to be orders. Uetz (2025) considers Amphisbaenia to be an suborder as with the lizards and snakes. (See Classification of reptiles.)
Worm lizards are normally classified into six families:
- Family Amphisbaenidae (Worm Lizards)
- Family Bipedidae (Two-legged Worm Lizards)
- Family Blanidae
- Family Cadeidae
- Family Rhineuridae
- Family Trogonophidae (Shorthead Worm Lizards)
ReferencesISBN links support NWE through referral fees
- Benton, M. J. 2024. Vertebrate Paleontology, 5th ed. Wiley. ISBN 978-1394195084
- Longrich, N. R., J. Vinther, R. A. Pyron, D. Pisani, and J. A. Gauthier. 2015. Biogeography of worm lizards (Amphisbaenia) driven by end-Cretaceous mass extinction Proc Biol Sci 282(1806): 20143034. Retrieved March 22, 2026.
- Uetz, P. 2025. Higher Taxa in Extant Reptiles The Reptile Database. Retrieved March 22, 2026.
External links
All links retrieved March 22, 2026.
- Amphisbaenia — Worm Lizards Wild Herps
- The Worm Lizard Reptiles Magazine
- Florida Worm Lizard Real Monstrosities
- Best Look Yet at Bizarre ‘Worm-Lizard’ Anatomy Jackson School of Geosciences
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