Sineoamphisbaena

Sineoamphisbaena is an extinct genus of squamate of uncertain phylogenetic placement. Its fossils are known from the Late Cretaceous deposits in Inner Mongolia, China. Wu et al. (1993), Wu et al. (1996) and Gao (1997) proposed and argued that it was the oldest known amphisbaenian; this, however, was challenged by other authors, such as Kearney (2003) and Conrad (2008), who instead assigned Sineoamphisbaena to the group of squamates variously known as Macrocephalosauridae, Polyglyphanodontidae or Polyglyphanodontia.

A large-scale study of fossil and living squamates published in 2012 by Gauthier et al. did not find evidence for a particularly close relationship between amphisbaenians and Sineoamphisbaena; in their primary analysis Sineoamphisbaena was found to be the sister taxon of the clade containing snakes, amphisbaenians, the family Dibamidae and the American legless lizard. The primary analysis of Gauthier et al. did not support a close relationship between Sineoamphisbaena and polyglyphanodontians either; however, the authors noted that when all snake-like squamates and mosasaurs were removed from the analysis, and burrowing squamates were then added individually to it, Sineoamphisbaena grouped with polyglyphanodontians. Gauthier et al. (2012) considered it possible that Sineoamphisbaena was a burrowing polyglyphanodontian.