International: Biostratigraphy, Biogeography, and Phylogeny of Vertebrates from the World's Oldest Known, Eutherian Dominated Fauna (Dzharakuduk, Uzbekistan)

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The 100m, Upper Cretaceous Dzharakuduk section (Kyzylkum Desert, Uzbekistan) includes river and marine sediments that yield over 100 species of vertebrates. Collecting microvertebrates at these sites was begun by the late Russian paleontologist Nessov and has been continued by an international consortium of Uzbek, Russian, British, American, and Canadian (URBAC) scientists. Large, new collections of marine invertebrate from the upper part of the section that can be correlated to type sections in Europe, indicate a Coniacian/Santonian age (about 85 million years old). This reconfirms that the underlying terrestrial vertebrates are at least 85-90 million years old, thus older than the more famous Gobi Desert sites. Locally abundant vertebrate remains are fragmentary, but often preserve exquisite detail. Most fossils were rapidly buried, possibly by flash floods, with little reworking. Paleoecology is similar to the Late Cretaceous North American coastal plains. Postcranial and cranial elements of pterosaurs, mammals, and dinosaurs remain common from the newly screened 55 tons of matrix. Among amphibians, salamanders are much more common than frogs. Among reptiles, aquatic turtles, and hadrosaur and tyrannosaur dinosaur fragments are common, while lizards, small theropod, ankylosaur, ceratopsian, and sauropod dinosaurs are relatively rare. Birds are diverse, including both extinct groups, as well as species closer to living birds. The rodent-like multituberculate mammals and relatives of marsupial mammals are rare. Eutherian mammals, the group of mammals to which humans belong, are the most common mammalian species at Dzharakuduk, with some 11 species. These include the world's earliest relatives of the group that gave rise to rodents and rabbits, as well as the group that may have given rise to at least seven orders of hoofed mammals and whales. All indications show that previous work has only begun to uncover the fossil riches of Dzharakuduk. The next three years of work there will provide answers to many of the remaining questions regarding these 85-90 million-year-old vertebrate faunas.