Dodson 9506694 Bone histology is a complex biological phenomenon. The nature of bone reflects phylogeny, ontogeny and events that punctuate the life history of the individual. Genuine progress in the study of dinosaur bone histology has resulted from disciplined studies of ontogenetic series of homologous bones. Such studies offer the best possible basis for physiological inferences about dinosaurs. Living and fossil ectotherms typically show bone structure termed lamellar-zonal, having wide zones alternating with narrow annuli, reflecting annual periods of rapid and slow bone deposition respectively. In living endotherms fibro-lamellar bone records rapid growth, typically without seasonal interruptions. Dinosaurs bone shows features characteristic of both endotherms and ectotherms. It is now evident that azonal fibrolamellar bone is not a character of basal dinosaurs, but is a derived character state that evolved independently several times in different lineages within the Dinosauria. Histology promises a privileged and powerful insight into dinosaur biology. In considering the paleobiology of dinosaurs, we will assess these animals on their own unique merits, without forcing them into stereotypes based on living endotherms and ectotherms. Four aspects of the proposed research are especially noteworthy: the standardized study of ontogenetic series of the same species; the phylogenetic study of the variation of bone tissue types; the stratigraphic distribution of bone types; and the investigation of the bone biology of living endotherms and ectotherms. In the proposed research the phylogenetic scope of growth series of dinosaurs will be extended to include basal dinosaurs , thyreophorans, and marginocephalians, as well as more derived forms such as hypsilophodontids, maniraptorans and basal birds. As a result, the evolution and distribution of bone types will be drawn into sharper phylogenetic focus than was previously possible. The proposed studies span the entire stratigrap hic distribution of dinosaurs, from the Late Triassic to the Late Cretaceous. A particularly valuable aspect of this study is the inclusion of growth series of the Chinese dinosaurs Lufengosaurus, Shunosaurus, and Protoceratops. Equally important, these studies will encompass a diverse array of extant ectotherms and endotherms. Studies of living animals of known environmental and biological history will elucidate factors that influence the structure of bone. The result of these investigations will be deeper insight into the phylogenetic and paleobiological significance of the histological structures of fossil bone.
