a member of Amphisbaenia, a lineage of mostly limbless burrowing lizards
known from the Paleocene onward. Amphisbaenians share a highly modified
skull architecture, a unique modification of the ear called the
extracolumella, and skin with annuli (rings, like a worm). There are four
major amphisbaenian groups: Bipedidae (the only lineage to have
forelimbs); Amphisbaenidae (the most diverse and widespread lineage);
Trogonophidae (a lineage that uses an oscillating excavation pattern); and
Rhineuridae (to which Rhineura belongs). Rhineuridae includes a
number of fossil forms (restricted to western North America), but only one
living species - Rhineura floridana - which occurs in central
Florida and Georgia.
Amphisbaenians, like other lizards (including
snakes), have paired evertible hemipenes, a transverse cloacal slit, and
shed their skin in its entirety. It is difficult to discern exactly where
amphisbaenians fit in the lizard family tree. Even the earliest-known
fossil representatives already exhibit the highly derived cranial
morphology of living amphisbaenians. Their skull is characterized by
remarkable adaptations for a burrowing lifestyle, in that it is solidly
built, with complex interdigitation of the sutures between bones. These
features, readily discernible in these CT-generated renderings of a fossil
Rhineura from the Oligocene White River Formation, are not found in
other lizards. Final resolution of the exact position of amphisbaenians
among lizards will require the discovery of older fossils which are less
Little is known of the lifestyle of living amphisbaenians
because of their burrowing habit. It is thought that most lay eggs and are
insectivorous. Males and females cannot be differentiated from external
appearance. Their modern distribution includes northern and sub-saharan
Africa, southwest Asia, the eastern and western Mediterranean, South
America east of the Andes, the West Indies, western Mexico, Baja
California, the southeasternmost United States, and
Estes, R., de Queiroz, K., and J.
Gauthier. 1988. Phylogenetic relationships within Squamata, pp.119-281. In
R. Estes and G. Pregill (eds.), Phylogenetic Relationships of the Lizard
Families. Stanford University Press, Stanford.
Gans, C. 1978. The
characteristics and affinities of the Amphisbaenia. Transactions of the
Zoological Society of London 34:347-416.
Gans, C. 1990. Patterns in
amphisbaenian biogeography: a preliminary analysis, pp. 133-143. In G.
Peters and R. Hutterer (eds.), Vertebrates in the Tropics. Museum
Alexander Koenig, Bonn.