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THE PHYLOGENETIC POSITION OF SINEOAMPHISBAENA HEXATABULARIS REEXAMINED

Abstract Sineoamphisbaena hexatabularis, a fossil squamate recovered from Upper Cretaceous deposits in Inner Mongolia, China, was reported to be the oldest known amphisbaenian and the sister group to all other amphisbaenians. However, the conclusion of amphisbaenian affinities was based on a partitioned analysis that excluded relevant data and included reconstructed characters. When characters for analysis are limited to those that are observable on the fossils and all evidence is included and analyzed simultaneously, results do not support S. hexatabularis as an amphisbaenian, but instead suggest that S. hexatabularis may be related to macrocephalosaurids. Several potential synapomorphies of S. hexatabularis and macrocephalosaurids are provided, including: presence of lateral process of palatal ramus of pterygoid; postorbital large, extending posteriorly beyond supratemporal fenestra, and approaching posterior edge of cranial roof; and tall, narrow, dorsal process of maxilla. S. hexatabularis is tentatively reassigned to the Macrocephalosauridae. The origin of amphisbaenians remains obscure.