12 The Early Cretaceous topographic evolution of Transbaikalia was largely governed by the 13 tectonic evolution of the Mongol-Okhotsk orogenic belt. The collapse of the Mongol-Okhotsk 14 orogen triggered the formation of metamorphic core complexes and associated extensional basins, 15 widespread throughout Transbaikalia, North Mongolia, and North China. Numerous lithofacies proximal sediment sources. Distal provinces also made a contribution to sedimentation indicating 29 the rise of a positive topography characterizing the exhumation of the metamorphic core 30 complexes. Overlying fine-grained formations indicate a significant smoothing of the topography, 31 suggesting that from middle Aptian, Western Transbaikalia developed in a relatively calm tectonic 32 regime. We also show that the basins of Transbaikalia were formed both in conjunction with the 33 exhumation of metamorphic cores complexes and reactivated structural sutures. Revised data on 34 dinosaur fauna and palynology, together with the dating of host deposits, provide insights on the 35 Early Cretaceous paleoenvironmental evolution.