Fig 1.- Iberian worm lizards (Blanus cinereus) by Richard Avery, from Wikipedia.
The worm lizards form a peculiar group of burrowing and legless reptiles that have a superficial resemblance to earthworms. These odd critters were traditionally placed in their own suborder, the Amphisbaenians, alongside the other two groups of Squamates, the snakes (Serpentes) and the lizards (Lacertilia). Molecular data (Townsend et al., 2004; Vidal et al., 2005) however have shown that they are in fact closely related to a particular family of old-world lizards, the Lacertidae (with representatives such as the European Green Lizard, Lacerta viridis and the common Wall Lizard, Podarcis muralis).
The fossil record of amphisbaenians is slim and their evolutionary history clouded with mystery. Previously, a paper published in Nature (Wu et al., 1993) described the taxon Sineoamphisbaena hexatabularis from the Upper Cretaceous of Inner Mongolia, as a stem amphisbaenian, but this conclusion turned out to be quite erroneous (Kearny, 2003).
Fig 2.- My reconstruction of Cryptolacerta hassiaca.
Now, a new Nature paper, written by Johannes Müller and co-workers present Cryptolacerta hassiaca from the Eocene Messel pit in Germany as a new ancestral amphisbaenian (Müller et al., 2011). Cryptolacerta is known from a single specimen consisting of a nearly complete articulated skeleton (missing only the end of the tail). It was small, very lizard-like in appearance but with relatively tiny limbs and a thickened skull. The structure of the skull of Cryptolacerta moreover supports the Lacertidae-Amphisbaenian molecular connection and indicates that skull reinforcement evolved before snake-like body in this particular group of headfirst burrowing reptiles.
Kearny, M. 2003. The phylogenetic position of Sineoamphisbaena hexatabularis reexamined. J. Vert. Paleont. 23, 394-403.
Müller J., Hipsley C.A., Head J.J., Kardjilov N., Hilger A., Wuttke M. & reisz R.R. 2011. Eocene lizard from Germany reveals amphisbaenian origins. Nature 473, 364-367.
Townsend, T.M., Larson, A., Louis, E. & Macey, J.R. 2004. Molecular phylogenetics of Squamata: the position of snakes, amphisbaenians, and dibamids, and the root of the squamate tree. Syst. Biol. 53, 735-757.
Vidal, N. & Hedges, S.B. 2005. The phylogeny of squamate reptiles (lizards, and amphisbaenians) inferred from nine protein-coding genes. C. R. Biol. 328, 1000-1008.
Wu, X.-C. et al. 1993. Oldest known amphisbaenian from the Upper cretaceous of Chinese Inner Mongolia. Nature, 57-59.