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Origin of Animals

The Doushantuo Formation in Guizhou Province (south China) contains microfossils which have been interpreted to represent the oldest evidence for animal life on Earth. Dave Bottjer, together with colleagues Junyuan Chen and Eric Davidson (as well as others), has been studying these fossils to determine their animal affinities, how they were preserved, and information about the ocean environments in which they lived. Recent studies have focused on using synchrotron radiation microtomography to obtain high resolution images of the exterior and interior of select fossils. This approach will provide a much greater level of understanding of the diversity of Doushantuo microfossils, many of which are animal embryos. Study of the Doushantuo biota, combined with evidence from molecular biology, promises to provide a much clearer picture of when in Earth history animals first evolved. In the Chengjiang area of Yunnan Province (south China) there is an Early Cambrian fossil deposit which preserves animals that lived in the oceans about 60 million years after the Doushantuo biota. The Chengjiang biota is very diverse and is a macrobiota that provides substantial evidence for the evolution of life during the "Cambrian explosion." Bottjer, together with his colleagues, has been studying the paleo-ecology of the Chengjiang animals, and the role that ecology played in this time of evolutionary diversification. Together, the Doushantuo and Chengjiang biotas represent extraordinary resources that allow us to decipher the evolutionary origin of animals on Earth.

Origin and Early Evolution of Birds

During the last two decades Luis Chiappe, along with his students and associates, has expended a great deal of effort on clarifying the century-old controversy of the origin of birds. This topic has been examined by analyzing fossil evidence from skeletons, eggs, bone histology, and soft-tissue of bird-like dinosaurs and primitive birds, many of them from China. All this evidence strongly supports the hypothesis that the closest relatives of birds are to be found among the carnivorous dinosaurs—animals akin to the renowned Velociraptor. Chiappe’s studies have also been extended to address the closely related question of the origin of avian flight, which he envisions as having originated within ground dwelling dinosaurs capable of flapping their feathered forelimbs while running. His studies of bird evolution—the late evolution of dinosaurs—have led to a comprehensive program on the diversity and genealogical relationships of Mesozoic birds. In the last few decades, the number of known species of early birds has more than tripled from those known for the previous century; most of these newly discovered primitive birds come from China. Chiappe and his associates have studied a host of different primitive lineages of birds that lived alongside large dinosaurs, and have analyzed important evidence for better understanding their evolutionary relationships, growth and development, and life histories.

 

 

Evolution of Mammalian Carnivores

Mammalian fossil carnivores consist of a large group of predators that play a very important role in the ecology of mammal communities. As top predators, fossil carnivores are generally rare due to their position within the food chain. However, a rich variety of fossil carnivores has been recorded from Chinese Cenozoic sediments, thus providing key information for better understanding the evolution of these fascinating mammals. Xiaoming Wang studies carnivores that have an inter-continental distribu-tion, such as skunks, saber cats, dogs, and hyenas. As predators, carnivores are often superb runners, an ability that permits them to have a wide distribution, sometimes over several continents. The dog family (canids) is one such group, and it has a worldwide distribution. Wang’s study of dogs led him to trace their ancestry to North America, and their eventual success in migrating to Eurasia, South America, and the rest of the world. His recent book, “Dogs: Their Fossil Relatives & Evolutionary History” (Columbia University Press; http://cup.columbia. edu/book/978-0-231-13528-3/dogs), chronicles the fossil history of this important group of carnivores.

Climatic History of the Tibetan Plateau

As the highest and largest plateau in the world, Tibet offers insights into many important climatic and biotic questions. This immense, towering landscape was created by the collision of the Indian plate into Eurasia. The process of mountain building and related climatic change profoundly affected the ancient biological communities that lived on or adjacent to the high plateau. Xiaoming Wang’s field work in Tibet is aimed at understanding the history of biological evolution as related to the uplifting of the Tibetan plateau. He leads a multinational and multidisciplinary team of geologists and paleontologists who attempt to recover fossil mammals and other fossils from several high altitude basins in Tibet. Thus far, they have found ancient mammals that are unique to the high plateau and strange extinct fishes that bear witness to dramatic changes in their environment.

Mass Extinctions

Since the great diversification of life on Earth 500-600 million years ago, several mass extinctions have occurred. The biggest occurred at the end of the Permian period, approximately 252 million years ago. This extinction was followed by the Early Triassic period which lasted approximately 5 million years. Environments on Earth were highly stressed during this time, and Earth's biota was unable to recover from the effects of the mass extinction. Only in the following Middle Triassic did recovery truly begin. China contains some of the best fossil sequences and sedimentary rocks in the world from which much can be learned about this end-Permian mass extinction and Triassic recovery. Dave Bottjer, together with a number of former Ph.D. students (Margaret Fraiser, Sara Pruss, Matthew Clapham, Pedro Marenco, Catherine Powers), has extensively studied this period of biotic crisis, including field studies of key stratigraphic sections and fossil sequences in China. This work has led to the development of a general theory that oceanic stratification, including anoxia and euxinia, coupled with the effects of the eruption of the Siberian Traps, were the major causes of this mass extinction interval.