Sauropodomorpha (dinosauria, saurischia) appendicular skeleton disparityTheorical morphology and compositional data analysis

Resumen

The appendicular skeleton of Sauropodomorpha was used as analysis object in a comparative context, along with other groups of Archosauria and Mammalia. The goal was to shed light on some aspects of the morphological evolution of Sauropodomorpha dinosaurs and, consequently, to explore some of the causes related to the mentioned morphological changes. Compositional data was obtained by measuring the length of several fore and hind limb elements and were employed and subsequently subjected to analytical methodologies based on Compositional Data Analysis (CDA). The database comprises about 600 entries and 2000 measured lengths. The CDA statistical tools were thoroughly presented, reviewed and experimentally applied to different biological contexts, with the objective of testing their applicability before submitting our own data to this technique. The use of this methodological approach aims to contribute to a better knowledge of the appendicular geometry of Sauropodomorpha, but simultaneously to explore, under a macroevolutionary perspective, the quantification of disparity and proportions morphospace occupation patterns of the fore and hind limb extremities in a vast sample of Amniota. Therefore, and based on CDA techniques, a new and rigorous morphospace disparity metric is proposed ¿ Aitchison Distance, which in turn allows the quantification and discernment of the dissimilarities observed not only among a group, but also between different groups occupying proportions morphospaces, as well as the identification of the variability specific to each bone under scope. The assumption of size as a variable will permit the refinement of the global approach and, in some cases, the identification of its relation towards disparity. Important questions, such as the changes in locomotion (from bipedalism to quadrupedalism) which took place in the evolutionary history of Sauropodomorpha and the gigantism issue unavoidable when focusing on some of the groups belonging to this clade are explored and interpreted under the scope of the CDA morphometric methodology. In order to better understand the amplitude of these changes, this study was extended to other dinosaur and mammal groups of bipedal and quadrupedal locomotion, and data concerning flying organisms was added to the analysis object, with the intent of creating a complete limb proportions morphospace integrating all of them: birds, bats, pterosaurs, theropods, ornithopods, artiodactyls, perissodactyls, carnivores and metatherians. The structure of this work is organized as follows: Chapter 1 (Introduction/Objectives) systematizes and contextualizes the conceptual and methodological backgrounds of this thesis, simultaneously relating them to its scientific objectives. Chapter 2 (Variation and Disparity metrics in ternary morphospaces) presents and reviews the CDA analysis techniques which will constitute the methodological working tools of the analysis. The concepts of theoretical and empirical morphospace are reviewed, as is the concept of disparity. Some examples are used herein to corroborate the legitimacy and relevance of this analytical methodology regarding compositional data. Chapter 3 (Studies under Compositional Data Analysis ¿ examples and re-analyses) reanalyzes previously published works employing CDA techniques. Biological and conceptual contexts as diverse as the geometrical tools used in a macroevolutionary perspective focusing on the Archosauria cranium or the occupation of limb proportions morphospaces in Pterosauria, Chiroptera and Aves are quantitatively reevaluated. Several analytical amplifications are performed, thus increasing and enriching the outcome results of the original researches, particularly concerning morphospaces occupation and disparity among flying tetrapods. Chapter 4 (Sauropodomorpha phylogenetic context and selected groups) offers a revision of the phylogenetic hypotheses formulated regarding the clade Sauropodomorpha and describes the selection criteria presiding over the selection of the groups included in the performed morphometric analyses. Capítulo 5 (Sauropodomorpha locomotion - evolutionary history and appendicular skeleton morphology) reevaluates some of the problematic issues concerning the appendicular skeleton morphological analysis of Sauropodomorpha: locomotion mode alterations regarding bipedalism and quadrupedalism, and also gigantism. The morphological characteristics of the diverse limb elements under analysis are also reviewed. Chapter 6 (Sauropodomorph Limb Disparity and Morphospaces) explores the proportions morphospaces in Sauropodomorpha, the disparity quantifications concerning the several groups selected among the clade and the relation between size and disparity, and also introduces the relation between morphological integration and variability. The changes in the locomotion patterns are analyzed according to the morphospace occupation patterns by the diverse groups and according to the variability observed when focusing on the different limb elements. Chapter 7 (Dinosauria and Mammalia Limb Disparity and Morphospaces) extends the methodological procedures already applied in chapters 3 and 6 to a much wider set of animals, thus aiming to achieve an estimation of a global proportions morphospace of the appendicular skeleton. Variability and size are evaluated and thereafter both statistically and phylogenetically confronted, in order to attempt a depiction of bipedal and quadrupedal animal groups. Morphological integration levels are proposed for each group.