SINEOAMPHISBAENA HEXATABULARIS, AN AMPHISBAENIAN (DIAPSIDA, SQUAMATA)FROM THE UPPER CRETACEOUS REDBEDS AT BAYAN-MANDAHU (INNER-MONGOLIA, PEOPLES-REPUBLIC-OF-CHINA), AND COMMENTS ON THE PHYLOGENETIC-RELATIONSHIPS OF THE AMPHISBAENIA

Sineoamphisbaena hexatabularis Wu et al., 1993 is the earliest known a mphisbaenian represented by well-preserved cranial and postcranial mat erial. It reveals a mosaic of generalized lizard-like features and amp hisbaenian characters. Most distinctive of the latter are features of cranial consolidation adaptive for a fossorial way of life. Phylogenet ic analyses strongly confirm the monophyly of the Amphisbaenia inclusi ve of S. hexatabularis. The Amphisbaenia is diagnosed by a suite of ap omorphic characters. The available evidence suggests a probable Amphis baenia-Macrocephalosauridae relationship within the Scincomorpha. This is supported primarily by the unique modifications of the palate and temporal region of the skull. It is argued here that the Amphisbaenia evolved in Central Asia during the Cretaceous, in response to the tran sition from a perennial lacustrine environment to a dry, semiarid eoli an environment. The relatively primitive morphology indicates that S. hexatabularis was not permanently subterranean. The further derived mo difications of later forms are associated with tunneling in an environ ment of more compact soils.