The East Gobi basin of Mongolia is a poorly described Late Jurassic-Early Cretaceous extensional province that holds great importance for reconstructions of Mesozoic tectonics and paleogeography of eastern Asia. Extension is especially well recorded in the structure and stratigraphy of the Unegt and Zuunbayan subbasins southwest of Saynshand, Mongolia, where outcrop and subsurface relationships permit recognition of prerift, synrift, and postrift Mesozoic stratigraphic megasequences. Within the synrift megasequence, three sequences developed in response to climatic and rift-related structural controls on sedimentation. Where best exposed along the

Two new specimens of the oviraptorid theropod Nemegtomaia barsboldi from the Nemegt Basin of southern Mongolia are described. Specimen MPC-D 107/15 was collected from the upper beds of the Baruungoyot Formation (Campanian-Maastrichtian), and is a nest of eggs with the skeleton of the assumed parent of Nemegtomaia on top in brooding position. Much of the skeleton was damaged by colonies of dermestid coleopterans prior to its complete burial. However, diagnostic characters are recovered from the parts preserved, including the skull, partial forelimbs (including the left hand), legs, and distal portions of both feet. Nemegtomaia represents the fourth known genus of oviraptorid for which individuals have been found on nests of eggs. The second new specimen, MPC-D 107/16, was collected a few kilometers to the east in basal deposits of the Nemegt Formation, and includes both hands and femora of a smaller Nemegtomaia individual. The two formations and their diverse fossil assemblages have been considered to represent sequential time periods and different environments, but data presented here indicate partial overlap across the Baruungoyot-Nemegt transition. All other known oviraptorids from Mongolia and China are known exclusively from xeric or semi-arid environments. However, this study documents that Nemegtomaia is found in both arid/aeolian (Baruungoyot Formation) and more humid/fluvial (Nemegt Formation) facies.

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large ornithopod footprints were found in the Nemegt Formation at the locality known as Nemegt in the Gobi of Mongolia. Additional hadrosaur ichnites, plus footprints of sauropods and theropods, have been recovered since then. The Nemegt Formation is known for the number and diversity of dinosaur skeletons found there, but footprints have never before been reported. Footprints were noted in three horizons within the formation, and occur at the top of upward-fining successions of floodplain sandstones and mudstones of a meandering fluvial paleoenvironment. Most of the footprints are preserved as natural casts that show good preservation of detail. Skin impressions are found on some, and many have slide marks. The vast majority of the footprints can be identified as having been made by Saurolophus, but two footprints each of Tarbosaurus and Opisthocoelicaudia were also recovered. Three hadrosaur footprints were found in the quarry of a Tarbosaurus skeleton. It appears that after the Tarbosaurus had died and been partially buried, its skeleton was trampled by a hadrosaur. The overwhelming domination of hadrosaurs at the footprint levels suggests there are preservational biases acting on the fossilization of Nemegt skeletons to produce abnormally high predator/prey ratios.

Structure of the manus and pes has long been a source of confusion in ankylosaurs