Taxonomic composition and systematics of Late Cretaceous lizard assemblages from Ukhaa Tolgod and adjacent localities, Mongolian Gobi Desert

Upper Cretaceous deposits at Ukhaa Tolgod and adjacent localities in the Mo ngolian Gobi Desert have yielded a large number of superbly preserved lizar d specimens, including representatives of several new taxa (described in th is paper) and important supplementary material of several previously poorly known taxa. Study of these specimens gives important insight into the taxo nomic diversity and systematics of the Late Cretaceous lizard fauna of the Gobi Desert. A preliminary survey indicates that the lizard assemblage from Ukhaa Tolgod and adjacent localities consists of some 30 species in four h igher groups (Iguania, Gekkota, Scincomorpha, and Anguimorpha). The iguania ns are documented by eight species, including three species newly recognize d in this paper. The Scincomorpha are the most diverse group, represented b y as many as 14 species including three new and II previously known species . The Anguimorpha are nearly as diverse as the Iguania, while the Gekkota i s the least diverse group with a single species documented in the assemblag e. The scincomorphs include forms that are highly specialized for burrowing life-styles, interpreted from their cranial morphology as possibly analogo us to extant species. The anguimorphs include phylogenetically important ba sal members of several major anguimorph clades. The paleoecological significance of these lizards cannot be overlooked. Acc ording to tooth morphology, most lizards are predatory in terms of habit, w hile true herbivorous species are rare. Most specimens are preserved as sku lls articulated with mandibles, but virtually complete skeletons in situ ar e quite common. Delicate parts of the skull, such as the braincase and ear ossicles, are undistorted and the surfaces of the bones show no sign of san d abrasion. These observations indicate not only relatively quick burial bu t also burial under relatively mesic climatic conditions with low-energy wa ter involved during the taphonomic process.