''Sineoamphisbaena'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

squamate Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest Order (biology), order of reptiles; most members of which are commonly known as Lizard, lizards, with the group also including Snake, snakes. With over 11,991 species, it i ...

of uncertain phylogenetic placement. Its fossils have been found in

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

deposits in Inner Mongolia, China. It contains a single species, ''Sineoamphisbaenia hexatabularis.''

Taxonomic affiliation

Wu ''et al.'' and Gao proposed and argued that ''Sineoamphisbaenia'' was the oldest known

amphisbaenia Amphisbaenia (called amphisbaenians or worm lizards) is a group of typically legless lizards, comprising over 200 extant species. Amphisbaenians are characterized by their long bodies, the reduction or loss of the limbs, and rudimentary eyes. A ...

n; this, however, was challenged by other authors, such as Kearney and Conrad, who instead assigned ''Sineoamphisbaena'' to the group of squamates variously known as Macrocephalosauridae, Polyglyphanodontidae or

Polyglyphanodontia Polyglyphanodontia, also known as the Borioteiioidea, is an extinct clade of Cretaceous lizards. Polyglyphanodontians were the dominant group of lizards in North America and Asia during the Late Cretaceous. Chronology and distribution Most pol ...

. A large-scale study of fossil and living squamates published by Gauthier ''et al.'' in 2012 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

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

s, amphisbaenians, the family

Dibamidae Dibamidae or blind skinks is a family of lizards characterized by their elongated cylindrical body and an apparent lack of limbs. Female dibamids are entirely limbless and the males retain small flap-like hind limbs, which they use to grip their ...

and the

American legless lizard The family Anniellidae, known as American legless lizards, contains six species in a single genus ''Anniella'': ''A. pulchra'' (California legless lizard), the rare ''A. geronimensis'' (Baja California legless lizard), and four more discovered in ...

. 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.'' considered it possible that ''Sineoamphisbaena'' was a burrowing polyglyphanodontian.

Sources

* ''World Encyclopedia of Dinosaurs & Prehistoric Creatures: The Ultimate Visual Reference To 1000 Dinosaurs And Prehistoric Creatures Of Land, Air And Sea ... And Cretaceous Eras (World Encyclopedia)'' by Dougal Dixon

References

{{Taxonbar, from=Q7522422 Prehistoric squamates Prehistoric reptile genera Late Cretaceous lepidosaurs of Asia Fossils of Mongolia