L’évolution des dinosaures sauropodomorphes et la radiation des grands sauropodes sont encore loin d'être comprises, ni même datées avec précision. Si les premiers sauropodes semblent apparaître à la fin du Trias, ils ne se diversifient qu'à partir du Jurassique moyen. L’incertitude entourant la définition à donner au clade Sauropoda est une des principales causes de l'absence de consensus quant à la transition prosauropodes – sauropodes. C’est ce problème du « stem-group » des sauropodes qui est abordé dans cette thèse. Certains prosauropodes sont ainsi aujourd’hui considérés comme des sauropodes à part entière par certains auteurs. Ces taxons basaux diffèrent cependant beaucoup selon les auteurs. La multiplication des analyses cladistiques n’a rien résolu puisque celles-ci n’ont jamais été comparées entre elles.La découverte en 2008, par une équipe du MNHN, dans le Jurassique inférieur du Lesotho, d'un squelette de prosauropode articulé sert ici de base à une étude anatomique et systématique des sauropodomorphes basaux. De nombreux autres restes de dinosaures inédits du Lesotho appartenant aux collections du MNHN viennent compléter le matériel d’étude. Parmi ceux-ci, du matériel rapporté au prosauropode de Maphutseng et des fossiles attribués au genre Meroktenos sont entièrement décrits en détail pour la première fois.Une comparaison critique et détaillée des analyses phylogénétiques antérieures a été réalisée en utilisant la méthode de cladistique comparée telle qu’elle a été formalisée par Sereno en 2009. Elle a permis de démontrer l’impact très important du choix des caractères et de leur codage sur la topologie des arbres. Suite à cela, un premier retour sur une liste compilée de 449 caractères a été effectué. Il a nécessité la vérification d’une matrice de 15 000 à 20 000 cellules, et plus de 1300 mesures. Ce retour aux caractères ont entraîné la suppression de plus d’une centaine de caractères, et la création d’une matrice inédite de 49 unités taxonomiques et 308 caractères. Les résultats de l’analyse phylogénétique de cette matrice, bien que préliminaires, soulèvent plusieurs points intéressants. Plusieurs clades, généralement retrouvés dans les analyses les plus récentes publiées par d’autres auteurs, n’apparaissent pas. En revanche, des clades qui n’avaient jusque-là jamais été retrouvés font leur apparition. Les différentes analyses pointent également du doigt le problème de l’origine des Sauropodomorpha, et relancent le débat sur l’origine du clade Sauropoda. / The evolution of sauropodomorph dinosaurs and the radiation of the large sauropods are still far from being understood and well-dated. If the first sauropods seem to appear at the end of the Triassic, they don’t start to diversify before the Middle Jurassic. The uncertainty surrounding the definition of the clade Sauropoda is one of the main causes of the lack of consensus regarding the prosauropod – sauropod transition. It is this issue of the “stem-group” of sauropods that is dealt with in this thesis. Some prosauropods are now considered to be sauropods by some authors. These basal taxa differ a lot depending on the authors. The multiplication of the cladistic analyses didn’t solve the problem as they never were compared.The discovery in 2008, by a MNHN team, in the Early Jurassic of Lesotho, of a prosauropod articulated skeleton is used herein as the basis for anatomical and systematic study of basal sauropodomorphs. Many other new dinosaur remains from Lesotho, housed in the MNHN collections, complement the study material. Among these, material referred to the Maphutseng prosauropod and fossils referred to the genus Meroktenos are described in details for the first time.A critical and detailed comparison of previous phylogenetic analyses is performed, using the comparative cladistics method as formalized by Sereno in 2009. This work allowed to highlight the significant impact of the choice of characters and their scoring on the topology of the trees. After that, a first reappraisal of a list of 449 compiled characters was carried out. It required the reexamination of a matrix consisting in 15 000 to 20 000 cells, and more than 1300 measures. This work led to remove more than one hundred morphological characters, and the building of a new matrix including 49 taxonomic units and 308 characters. The results of the phylogenetic analysis, although preliminary, raise some interesting points. Several clades, often recovered in the most recent analyses published by other authors, are not recognized here. However, clades that had, until then, never been found, are recovered. The different analyses also point out the hurdle of the origin of Sauropodomorpha, and reopen the debate on the origin of Sauropoda.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-02-16T14:09:38Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) 1.UNIVERSIDADE FEDERAL DE PERNAMBUCO - PDF.pdf: 2290380 bytes, checksum: 779f1a4fa95fe4cc4bf311af3f117d25 (MD5) / Made available in DSpace on 2017-02-16T14:09:38Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) 1.UNIVERSIDADE FEDERAL DE PERNAMBUCO - PDF.pdf: 2290380 bytes, checksum: 779f1a4fa95fe4cc4bf311af3f117d25 (MD5) Previous issue date: 2016-03-04 / CAPES / Apresentamos uma descrição detalhada da morfologia e osteohistologia de pequenos ossos de Arcosauromorpha encontrados da Zona de Associação de Hyperodapedon, referente à Sequência Santa Maria II, Supersequência Santa Maria, Triássico Superior do Rio Grande do Sul, Brasil. O material é composto por ossos de tamanho reduzido, com dimensões menores do que 57mm, encontrados associados in situ. O espécime é composto por um úmero e um metatarsal III direitos, extremidade proximal de uma falange ungueal, um arco neural quase completo de uma vértebra pré-sacral e um centro vertebral pré-sacral. Comparações morfológicas entre UFSM11326 e outros organismos do Triássico mostraram se tratar de um dinossauriano, com possível associação ao grupo Sauropodomorpha. São elas: morfologia da crista deltopeitoral do úmero apresentando prolongamento do cume na crista deltoide; eixo de torção das porções proximal e distal do úmero; morfologia do metatarsal III, apresentando ângulo de torção entre as extremidades proximal e distal superior a 60° e presença do ombro medial; posições da diapófise, parapófise e das infracavidades diapofisiais restantes no arco neural. Este grupo de arcossauros já foi registrado anteriormente em estratos triássicos da Supersequência Santa Maria. As análises do fechamento das suturas do arco neural indicaram um indivíduo jovem, com suturas abertas em forma de zíper. As sessões finas da diáfise do úmero e do metatarsal III, corroboram este estado ontogenético, indicando se tratar de um espécime em fase inicial de desenvolvimento. Exibiu um complexo ósseo fibrolamelar (comum em espécimes dinossaurianos), composto por ósteons primários, sem ocorrência de marcas de crescimento (LAGs ou annuli), áreas extensas de reabsorção ou a presença de lamelas circunferenciais externas (external fundamental system = EFS). Este padrão evidencia uma estratégia de crescimento rápido, sustentado por elevadas taxas metabólicas, superiores a dos répteis modernos, e comparáveis com aquelas já encontradas para este grupo de arcossauros. Definimos portanto que UFSM11326 corresponde a um Sauropodomorpha jovem, sem a conclusão de seu crescimento assintótico, com elevados níveis de deposição óssea e consequente crescimento acelerado até o momento de sua morte. / Here we present a detailed description of the morphology and osteohistology of small bones of Arcosauromorpha found at the Hyperodapedon Association Zone, referring to the Santa Maria II Sequence, Santa Maria Supersequence, Upper Triassic of Rio Grande do Sul States, Brazil. The material consists of small sized bone (dimensions smaller than 57mm) found associated in situ. The specimen consists of a right humerus and metatarsal III, proximal extremity of an ungueal phalanx, an almost complete neural arch of a pre-sacral vertebra, and a pre-sacral vertebral center. Morphological comparisons between UFSM11326 and other organisms from Triassic revealed that it is a dinosaurian, possibly related to Sauropodomorpha group. The similarities include the morphology of the deltopectoral humerus crest that has an extension of the deltoid crest; twist axis from proximal and distal portions of the humerus; morphology of metatarsal III with torsion angle between the proximal and distal extremities greater than 60° and medial shoulder; positions of the infracavities of the apophysis, parapophysis and diapophysal remaining at neural arch. This archosaurs group has already been registered previously in Triassic strata of the Santa Maria Supersequence. The analyses of the closure of the sutures of the neural arch indicate it to be a young individual with open sutures zipper-shaped. The final sessions of the humeral diaphysis and metarsal III corroborate this ontogenetic state, showing it to be a specimen at an early stage of development. A fibrolamellar bone complex that is common in dinosaurian specimens is present, composed of primary osteons, without occurrence of growth marks (LAGs or annuli), extensive reabsorption areas or external circumferential lamellas (external fundamental system = EFS). This pattern shows a rapid growth strategy, supported by high metabolic rates that are greater than in modern reptiles and comparable with those already found to this archosaurs group. We conclude that UFSM11326 corresponds to a young Sauropodomorpha without completing its asymptotic growth and with high levels of bone deposition and subsequent rapid growth until the moment of his death.

For 130 years dinosaurs have been divided into two distinct clades – Ornithischia and Saurischia. This dissertation looks at the earliest evolution of the clade Dinosauria by focusing upon the interrelationships of the major subsidiary clades within it. It does this following examination, comparison and description of early dinosaur material, and by utilising modern phylogenetic analysis techniques, to rigorously and objectively test the fundamental groupings within the clade Dinosauria using a newly compiled dataset of early dinosaurs and other dinosauromorphs (= close dinosaur relatives). The current consensus on how the principal clades within Dinosauria (Theropoda, Sauropodomorpha and Ornithischia) are related to one another is challenged by the results of these analyses. This study finds, for the first time, a sister-group relationship between Ornithischia and Theropoda, here termed Ornithoscelida. Consequently, a new definition for Dinosauria is presented, as the historic definition would exclude all members of Sauropodomorpha from the clade. As well as this, I propose revisions to the definitions of each of the principal dinosaurian sub-divisions and propose a new timeframe and geographic setting for the origin of Dinosauria. These new hypotheses force re-evaluations of early dinosaur cladogenesis and character evolution, suggest the independent acquisition of hypercarnivory in multiple dinosaur groups and offers an explanation for many of the anatomical features previously regarded as striking convergences between theropods and early ornithischians. As well as presenting new anatomical data on many early dinosaurs and dinosauromorphs, including a comprehensive re-description of the postcranial anatomy of Lesothosaurus diagnosticus (Chapter 2), and a new anatomical dataset of early dinosaurs (the largest ever compiled), this thesis goes on to implement the new dataset to investigate a number of important outstanding questions about early dinosaur evolution and provides new lines of enquiry for future workers to pursue. The results of this thesis reveal the oldest known members of the dinosaurian clades Theropoda and Sauropodomorpha (Chapter 6), as well as a new clade within Ornithischia; a taxon previously thought to represent a derived theropod has been recovered as a potential ‘missing link’ between theropods and ornithischians using the new dataset. This work now provides a unique tool for the assessment of the phylogenetic affinities of early dinosaurs and dinosauromorphs and, once published, will hopefully become the benchmark dataset for palaeontologists working in this area.