Anatomy and relationships of stem group salamanders from the middle jurassic of Mongolia

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Modern salamanders provide the best living models of the anatomy and way of life of animals that evolved from archaic fish into the first terrestrial vertebrates 365 million years ago. Most hatch from aquatic eggs, spend their early life in the water and metamorphose to terrestrial adults. Unfortunately, there has been a gap in our knowledge of the fossil record of 200 million years between the oldest known modern salamanders and their possible ancestors among ancient amphibians. Within the last 15 years, this gap has been bridged by a host of fossils from deposits as old as 165 million years, at the base of the Jehol Biota in Inner Mongolia and adjacent China that yield fossils of feathered dinosaurs, some of the oldest mammals and archaic birds. Because of the rapid burial of their bodies in anoxic sediments from repeated volcanic eruptions, the salamander remains are exquisitely preserved, including scores of complete, articulated skeletons, growth stages from larvae to adults, impressions of the eyes, external gills, and muscles. In some the skin exhibits its original texture, the pattern of pigment distribution and costal grooves that in terrestrial salamanders conduct water from the ground to the sides of the body to assist in cutaneous respiration. Scores of specimens are available for study in cooperation with the Inner Mongolian Provincial Museum. At least five, highly divergent lineages are known from the Daohugao locality that will be illustrated, describribed, and compared in detail with their putative ancestors among ancient amphibians, salamanders from elsewhere in the Jehol sequence and modern salamander families, with the assistance of gratuate and postdoctoral students and professional colleagues who are knowledgable in the anatomy, physiology, ontogeny and behavior of modern salamanders. This study will vastly improve our understanding of the relationships and of evolution among all salamanders throughout their history.