Cretaceous Mongolia
Cretaceous Mongolia is one of the strangest and best preserved of all Mesozoic ecosystems. The shifting sand of what was, even then, the Gobi Desert have ensured that fossils of the animals that lived there can be found in exactly the position in which they were buried, with most of the bones together. The most notable fossil is the very well preserved remains of a "Velociraptor", locked in combat with a "Protoceratops", a small ceratopsian. Dinosaurs in Mt. Altai. Mt. Altai is unusual because the comparative lack of food means that most of the dinosaurs there remained quite  small, most not much bigger than a present-day person. There were a few large dinosaurs, though. "Tarbosaurus" was the Mongol equivalent of "Tyrannosaurus rex" and was almost as large. The large herbivores grew into many strange shapes. "Therizinosaurus" was a bipedal herbivore about as tall as "Tarbosaurus" with a long neck, small head and characteristic long claws on the hands which it used for defence and to help it browse far away trees. Small ankylosaurs were the armour-plated residents and hadrosaurs provided large prey for the carnivores. Unusual prehistoric animals, such as the "Oviraptor", fed on many of  the same things that "Velociraptor" did. The two species often competed for food. The Gobi Desert was often interspersed with scrubland and occasionally a dense rainforest supporting many types of plant life, insects, and small dinosaurs like "Mononykus". "Mononykus" and the "Velociraptor" were among the dinosaurs that are taxon related to modern birds.