Morphometric analysis of evolution and growth in the ceratopsian postcranial skeleton.

摘要

The cranial anatomy of ceratopsian (“horned”) dinosaurs is well understood, but the postcranial skeleton has been largely ignored in previous studies of phylogeny and growth. This project applies a variety of morphometric techniques to the study of the ceratopsian girdle and limb elements, in order to document changes within a phylogenetic context through evolution and growth of these elements.; In order to study differences in shape of the ceratopsian postcranial elements and to compare evolutionary and developmental patterns, multivariate (Principal Component Analysis) and bivariate methods were used to analyze linear measurement data, and the shape methods Resistant-Fit Theta-Rho Analysis (RFTRA), Least-Squares Theta-Rho Analysis (LSTRA), and Euclidean Distance Matrix Analysis (EDMA) were applied to biological landmark data.; Results of the analyses show that in this group of dinosaurs, size is the primary change through evolution of the skeleton. Elements increased through evolution with positive allometry, and increasing structural support is evident, especially in the radius and fibula.; Phylogenetically, the ceratopsian postcrania agree with the skull material included in recent cladistic analyses. Psittacosaurus elements are in many ways derived relative to those of non-ceratopsid neoceratopsians, and evidence suggests that Psittacosaurus was bipedal, while non-ceratopsid neoceratopsians were not, except maybe for Udanoceratops . With increasing body size, neoceratopsian limbs bowed laterally.; Results of the growth analyses show that although ontogeny does not recapitulate phylogeny in this clade, growth trends are nearly identical to evolutionary trends in the elements studied. Heterochronic trends are exhibited in the ceratopsian postcranial skeleton, primarily as peramorphosis. Avaceratops is determined to be a valid taxon based on differences in the postcranial skeleton, but Brachyceratops is most likely a juvenile form of another taxon.; The variety of methods allows for unbiased interpretation of results, provide more information than any one method, and provide controls for each other. However, sample sizes, especially for the growth analyses, are not ideal, and all results should be treated with caution at this time.