* Family Amphisbaenidae (Worm Lizards)
* Family Bipedidae (Two-legged Worm Lizards)
* Family Blanidae (see Amphisbaenidae)
* Family Cadeidae (see Amphisbaenidae)
* Family Rhineuridae (see Amphisbaenidae)
* Family Trogonophidae (Shorthead Worm Lizards)
Phylogenetic relationships according to Vidal et al. (2007)
Phylogenetic relationships according to Macey et al. (2004)
Single most parsimonious tree based on the analysis of 11,946 aligned nucleotide positions containing 5797 phylogenetically informative sites from 13 protein coding and 22 tRNA genes. Note that Gondwanan taxa, Trogonophidae (Diplometapon), and Amphisbaenidae (Amphisbaena and Geocalamus), are monophyletic. The two Laurasian families Rhineuridae (Rhineura) and Bipedidae (Bipes) represent successive, paraphyletic basal lineages indicating that amphisbaenian reptiles predate the breakup of Pangaea 200 million years ago. Modified from Figure 4 in Macey et al. (2004).
Order Squamata
Suborder Amphisbaenia
Trogonophis wiegmanni;
© Axel Kwet
Content: 4 genera with 6 species
Appearance: Trogonophids can be distinguished from other amphisbaenians by their triangular cross section. In addition they have acrodont teeth as opposed to pleurodont teeth in other amphisbaenians (in acrodont vertebrates teeth are attached to the apex = acron of the dentaries, maxillae, or premaxillae, whereas pleurodont species have their teeth attached to the medial surface of the bone). They lack caudal autonomy which is present in most other amphisbaenians. Snout strongly flattened snout with slightly upturned edges.
Diagnosis: Acrodonty, an enlarged sternal plate, an elongated nasal process of the premaxilla, scapulocoracoids bent posteriorly, short tail, absence of caudal autotomy, and a strong craniofacial angle (also present in rhineuroids). [After Kearney 2003].
Size: 8-24 cm snout-vent length.
Distribution: Turkey, Northern Africa, Somalia and the Middle East.
Behavior: Burrowing; unlike the other amphisbaenians, trogonophids use their tail as a brace to support the backward thrust of their digging. Their burrows match the shape of their noncircular bodies. They create their burrow by an alternating rotational movement of the head, which simultaneously shaves off the sides of the tunnel and compacts the wall.
Reproduction: oviparous, except the live-bearing Trogonophis
Relationships and sytematic notes: Trogonophids are the most divergent amphisbaenians. Vanzolini (1951) diagnosed this group (his subfamily Trogonophinae) based on acrodont dentition. Gans (1960) elevated the subfamily to family status. He also listed many characters in support of the monophyly of Trogonophidae: acrodonty, ossification of the extracolumella, a relatively short and stout body, and lack of caudalautotomy, among others. The monophyly of the trogonopids has been confirmed by Kearney (2003) who also included the fossil genus Listromycter, which was previously assigned to the Amphisbaenidae. See the Amphisbaenidae page for a phylogenetic tree that includes the Trogonophidae.
Order Squamata
Suborder Amphisbaenia
Bipes biporus
© Wayne van Devender
Appearance: While all other amphisbaenians have lost their limbs, members of the family Bipedidae have retained their forelimbs (bi = two; pes, latin = foot). In fact, they even develop supernumerary phalanges on their forelimbs which are used for burrowing.
Diagnosis: Fused fronto-parietal complex, anteriorly shifted pectoral girdle and forelimbs, polyphalangy of digit I (after Kearney 2003).
Size: 12-26 cm snout-vent length.
Distribution: The family with its single genus Bipes is restricted to Mexico. Some authors reported Bipes from the southwestern United states but they have never be confirmed.
Habitat: burrowing in desert soil.
Behavior: no information available.
Reproduction: oviparous with small ctutches of one to four eggs.
Phylogenetic relationships: See the Amphisbaenidae page for a phylogenetic tree that includes the Bipedidae.
Order Squamata
Suborder Amphisbaenia
Content: about 160 species in 18 genera (see list below).
Appearance: Amphisbaenians are limbless squamates whoses pectoral and pelvic girdles have been significantly reduced or are absent. Usually they have a distinctly annulated pattern of scutellation and rather short tails. Amphisbaenids are adapted to a burrowing life style and accordingly, their skulls are heavily ossified and their brain is entirely surrounded by the frontal bones. In contrast to other limbless lizards or snakes, which have a reduced left lung, the right lung of amphisbaenians is reduced in size.
Size: The total body length ranges from 10 cm to about 70 cm.
Distribution: Mostly Africa and South America with a few species in Europe and North America.
Habitat: Soil.
Behavior: Burrowing; The blunt-cone or bullet-headed genera (e.g., Amphisbaena, Blanus, Cadea Zygaspis) burrow by simple head-ramming. The spade-snouted taxa (Leposternon, Monopeltis) tip the head downward, thrust forward, and then lift the head. The Iaterally compressed keeled-headed taxa (Anops, Ancylocranium) ram their heads forward, then alternately swing it to the teft and right (Zug 1993).
Reproduction: usually oviparous, but some are live-bearing (namely some Loveridgea and Monopeltis).
Photo (left): Blanus cinereus; © Jakob Hallermann.
Relationships and sytematic notes: Rhineura is often put in a separate family, Rhineuridae. Kearney (2003) suggested to put Blanus in a separate family as well, the Blanidae, which can be diagnosed by their anteriorly truncated nasal bones and reduced clavicles (Kearney 2003).
Kearney (2003) also suggested to include the genera Aulura, Dalophia, Leposternon, and Monopeltis in the superfamily Rhineuroidea which she diagnosed by the following characteristics: strong craniofacial angle (also occuring in trogonophids), enlarged pectoral scales, a ventrally deflected retroarticular process, striated neural arches, denticulate posterior margins of the trunk vertebrae, ilium curving medially around anterior edge of vent, and an enlarged U-shaped occipital condyle.
Note that Kearney's Rhineuridae contains 1 extant genus, Rhineura, and 9 extinct genera (Dyticonastis, Hyporhina, Jepsibaena, Macrorhineura, Oligorhineura, Oligodontosaurus, Ototriton, Pseudorhineura, Spathorhynchus). Kearney's diagnosis of the Rhineuridae uses the following characteristics: small medial nasal process of premaxilla that does not separate the nasals in superficial view, a squared-off anterior edge of the snout, external naris opens ventrally, pterygoid-vomer contact, high maxillary tooth count, low maxillary tooth count, dentary process of coronoid overlapping dentary, and absence of posterodorsal rib processes. However, not all of these features can be ascertained in all the fossil taxa in this group.
Recently, Vidal et al. (2007) found that the genus Cadea is only distantly related to Amphisbaena in which it had been included previously. These authors erected a new family for the genus, Cadeidae Vidal & Hedges 2007.
