Sineoamphisbaena hextabularis (IVPP V10.593 (= V10593-I, Wu et al. 1993) Late Cretaceous ~ was considered close to Macrocephalus (= Gilmoretia). Derived from a sister to Chalcides, Sineoamphisbaena was a phylogenetic predecessor to Crythiosaurus and other burrowing lizards including Bipes.

Distinct from Chalcides ocellatus, the skull of Sineoamphisbaena was much shorter, both in the rostrum and postorbital areas. The orbit was much smaller, surround by more robust bones. The mandibles were considerably shortened to about half the skul length and the quadrates were rotated 90 degrees posteriorly to facilitate this. The upper temporal fenestra were small round holes. The lacrimal was fused to the prefrontal. The jugal was fused to the postorbital. The posterior skull was inflated and the basiocciput extended to more than half the skull length. The vomers extended to the basisphenoid. It is possible that the squamosal and postfrontal were fused. Unfortunately a crack appears there in the holotype skull.

The ribs were robust. The torso length is unknown. The humerus was proportional to the skull and pectoral girdle.

Cryptolacerta (Müller et al. 2011) was proposed as an amphisbaenian predecessor, but it nests here as a Heloderma predecessor.

Above is the skull of Sineoamphisbaena as originally identified and with some bones reidentified with comparisons to the more "normal" skink, Chalcides. Note the bone bordering the posterior upper temporal fenestra is the squamosal in each case. Note also the long jugal of Sineoamphisbaena can be replaced with the jugal + postorbital of Chalcides. Another case of jugal + postorbital fusion may have occurred in the basal lepidosaur, Carusia. Here is where the rotation of the quadrate took place. Note the unusual medial orientation of the upper teeth.

Kearney M 2003. The Phylogenetic Position of Sineoamphibaena hextabularis reexamined. Journal of Vertebrate Paleontology 23 (2), 394-403

Wu XC., Brinkman DB, Russell AP, Dong Z, Currie PJ, Hou L, and Cui G 1993. Oldest known amphisbaenian from the Upper Cretaceous of Chinese Inner Mongolia. Nature (London), 366: 57 - 59.

Wu X-C Brinkman DB and Russell AP 1996. Sineoamphisbaena hexatabularis, an amphisbaenian (Diapsida: Squamata) from the Upper Cretaceous redbeds at Bayan Mandahu (Inner Mongolia, People's Republic of China), and comments on the phylogenetic relationships of the Amphisbaenia. Canadian Journal of Earth Sciences, 33: 541-577.

Gao K 1997. Sineoamphisbaena phylogenetic relationships discussed. Canadian Journal of Earth Sciences. 34: 886-889. online article

Müller J, Hipsley CA, Head JJ, Kardjilov N, Hilger A, Wuttke M and Reisz RR 2011. Eocene lizard from Germany reveals amphisbaenian origins. Nature 473 (7347): 364–367. doi:10.1038/nature09919

wiki/Sineoamphisbaena