SYSTEMATICS AND TAXONOMIC DIVERSITY OF SQUAMATES FROM THE UPPER CRETACEOUS DJADOCHTA FORMATION, BAYAN-MANDAHU, GOBI-DESERT, PEOPLES-REPUBLIC-OF-CHINA

Squamate fossils collected for the Sino-Canadian dinosaur expeditions (1986-1990) include some 70 specimens from the Upper Cretaceous (Campa nian) Djadochta Formation, exposed at the vicinity of Bayan Mandahu, I nner Mongolia, China. Well-preserved skulls, jaws, postcranial skeleto ns, and even osteodermal armor document a fossil assemblage composed o f at least 18 genera in 8 families. Besides showing considerable taxon omic diversity, several families recorded in the assemblage are of imp ortance in understanding the geologic and biogeographic distribution o f the relevant groups, and the paleoenvironment in which these lizards lived. Comparison of the Gobi lizard assemblage with North American a nd Central Asian assemblages is briefly discussed. Taxonomic differenc es in the assemblage from that of the Upper Cretaceous in the North Am erican Western Interior reflect endemism and suggest a low frequency o f interchange of small terrestrial vertebrates between the two regions during Campanian time. The taphonomic setting of the squamate fossils indicates quick burial in arid to semiarid environments in the Gobi D esert, differing importantly from the Western Interior of North Americ a, where the accumulation of disarticulated jaw fragments reflects pos tmortem decomposition and fluvial transportation under subtropical to warm temperate conditions.