Dissertations / Theses on the topic 'Dinosaurs - Phylogeny'

The Elliot Formation of South Africa and Lesotho contains one of the most important but relatively understudied, early ornithischian faunas; here a review is presented of its known ‘fabrosaurid’ (non-heterodontosaurid) specimens. The first ornithischian collected from the Lower Elliot Formation (Late Triassic) is described, representing a new taxon of basal ornithischian. Within the Upper Elliot Formation (Early Jurassic), ‘Fabrosaurus australis’ is considered a nomen dubium, a new diagnosis of Lesothosaurus diagnosticus is presented, and a new taxon, Stormbergia dangershoeki gen. et sp. nov., is described. A comprehensive new cladistic analysis tests global ornithischian phylogeny. Results support the generally understood framework of ornithischian interrelationships; however, support is weak for many major clades, and the positions of certain taxa differ significantly from previous analyses. The enigmatic clade Heterodontosauridae may represent some of the most basal known ornithischians. Strong evidence supports hysilophodontid paraphyly, with some Middle Jurassic taxa (Agilisaurus, Hexinlusaurus) cladding as sister taxa to Cerapoda (Marginocephalia + Ornithopoda). Biogeographical analyses support hypotheses of vicariance related to the Late Jurassic geographical isolation of Asia. Synthesis of anatomical, taxonomic, phylogenetic, and biogeographical data allows the development of a broad overview of early ornithischain evolution. Triassic ornithischians were scarce and geographically limited. Ornithischians underwent a significant increase in diversity, abundance, and geographical distribution across the Triassic-Jurassic boundary, perhaps coincident with the origin of the clade Genasauria.

Tanius sinensis Wiman, 1929 was one of the first hadrosauroid or “duck-billed” taxa erected from China, indeed one of the very first non-avian dinosaur taxa to be erected based on material from the country. Since the original description by Wiman in 1929, the anatomy of T. sinensis has received relatively little attention in the literature since then. This is unfortunate given the importance of T. sinensis as a possible non-hadrosaurid hadrosauroid i.e. a member of Hadrosauroidea outside the family of Hadrosauridae, living in the Late Cretaceous, at a time when most non-hadrosaurid hadrosauroids had become replaced by the members of Hadrosauridae. To gain a better understanding of the anatomy of T. sinensis and its phylogenetic relationships, the postcranial anatomy of it is redescribed. T. sinensis is found to have a mosaic of basal traits like strongly opisthocoelous cervical vertebrae, the proximal end of scapula being dorsoventrally wider than the distal end, the positioning of the ventral apex of the supra-acetabular process of the ilium, posterodorsally to the ischial peduncle, the ratio between the proximodistal length of the metatarsal III and the mediolateral width of this element being greater than 4.5. Derived traits present in T. sinensis include curved dorsal surface of the scapula, arcuate fourth trochanter of the femur, cnemial crest of the tibia extending ventrally into the proximal half of the shaft, and the distal end of the fibula expanding into a club shape in lateral view. A potential autapomorphy is noted, being the caudal fusion of the medial and lateral condyles of the femur forming a completely enclosed “tunnel”. The body mass of the holotype of T. sinensis, is also estimated, and found to have been around 2950 kg. The phylogenetic analysis agrees with previous studies placing T. sinensis as a non-hadrosaurid hadrosauroid. Furthermore, in the phylogenetic analysis, T. sinensis is recovered as non-hadrosaurid hadrosauroid, forming a clade with Bactrosaurus johnsoni Gilmore, 1933, which shares the following unambiguous synapomorphies; the width of the orbital margin of the jugal being almost equally wide to that of the infratemporal margin of the bone; the ratio between the mediolateral width of the skull roof across the postorbitals and that across the quadrate cotyli of the paired squamosals being more than 1.20.
Den här uppsatsen handlar om Tanius sinensis Wiman, 1929 som levde under Kritaperioden i  Shan-dongprovinsen i nordöstra Kina. Tanius sinensis hörde till gruppen ”Anknäbbsdinosaurier” som ut- vecklades under början av Kritaperioden för mellan 130-100 miljoner år sedan. I slutet av Kritaperi- oden för ungefär 84 miljoner år sedan så blev de ”primitiva” ”anknäbbsdinosaurierna” bortträngda av de mer ”avancerade” ”anknäbbsdinosaurierna”. Tanius sinensis är viktig på så vis att den kan ha varit en ”primitiv” ”anknäbbsdinosaurie” som överlevde vid en tidpunkt när de flesta andra ”primitiva” ”anknäbbsdinsoaurier” hade trängts undan. För att få en bättre bild av T. sinensis anatomiska känne- tecken och en bättre bild av dess släktskapsförhållanden, så ombeskrivs anatomin hos den del av skelettet som inte omfattar kraniet. En släktskapsanalys görs också baserat på de kännetecken som jag själv och tidigare forskare  har  observerat  i  skelettet.  De  anatomiska  observationerna avslöjar en mosaik av ”primitiva” och mer ”avancerade” karaktärer, som tillsammans  med släktskapsanalysenpekar  på att T. sinensis var en sent överlevande ”primitiv”  ”anknäbbsdinosaurie”.

The Middle Jurassic was a critical time in the evolution of theropod dinosaurs, highlighted by the origination and initial radiation of the large-bodied and morphologically diverse Tetanurae. Middle Jurassic tetanurans are rare but have been described from Europe, South America, and China. In particular, China has yielded a number of potential basal tetanurans but these have received little detailed treatment in the literature.

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.

Parmi les dinosaures, le clade des Ornithopodes est l’un de ceux qui a rencontré le plus de succès. Apparus au Jurassique supérieur, le groupe s’est dispersé et diversifié jusqu’à sa disparition à la fin du Crétacé. Je me suis attachée à étudier le cerveau des Ornithopodes d’Europe et d’Asie, à établir des comparaisons avec les autres archosaures et de nouveaux arbres phylogénétiques incluant des caractères issus de l’endocrâne. Pour ce faire, des moulages et des reconstitutions à partir de données CT-scan ont été réalisées pour étudier la cavité endocrânienne de divers membres de ce groupe. J’ai réalisé des moulages endocrâniens en silicone de 3 taxons et les reconstructions à partir de données CT-scan de 3 autres taxons de Dinosaures Ornithopodes. Une collection unique d’endocrânes de crocodiles et d’oiseaux récents étend les possibilités de comparaison. Certains endocrânes des taxons fossiles ont confirmé les caractéristiques décrites précédemment dans la littérature, tandis que de nouveaux éléments sont apparus. Les endocrânes n’ont en effet pas seulement livré la morphologie du cerveau, mais aussi des valleculae, le détail des nerfs crâniens et de la glande pituitaire. J’ai ainsi pu étendre la présence de valleculae, qui est un indice fort en faveur d’un télencéphale développé, chez un nouvel Hadrosauroidea, alors que cela n’était connu que chez les Hadrosauridae et les membres dérivés de deux autres groupes (Theropoda et Pachycephalosauria). Le cerveau des Ornithopodes dérivés était caractérisé par des hémisphères cérébraux très larges et de forme arrondie. Les flexions crâniale et pontine sont inexistantes, à l’opposé de ce qui est observé chez les Saurischiens. Les pédoncules olfactifs étaient larges. J’ai également fourni de nouveaux exemples de l’influence de la taille de la glande pituitaire sur la taille totale de l’individu. Le cerveau des Ornithopodes a subi des changements au cours de leur évolution :le plus marquant est l’augmentation du volume des hémisphères cérébraux par rapport au reste du cerveau. J’émets l’hypothèse que cette augmentation résulte de la complexification des comportements chez les Ornithopodes.

Une nouvelle phylogénie a été établie, bénéficiant de l’apport de nouveaux caractères basés sur l’endocrâne. Elle apporte des éléments de réflexion intéressants quant à la position de plusieurs taxons d’Iguanodontia basaux. La résolution est cependant faible et d’autres études devront être menées dans le futur. Les relations de parenté ne sont pas stables et de faibles changements entraînent des différences notables dans les résultats des analyses phylogénétiques./Among the Dinosauria, Ornithopoda were one of the most successful clade. Since the Late Jurassic, they spread and diversified until the end of the Cretaceous. I studied the brain of Ornithopoda from Europe and Asia, established comparisons with other archosaurs and new phylogenetic analyses including endocranial characters. In order to do this, I made silicone endocasts of 3 taxa and virtual reconstructions from CT-scan dataset of 3 other taxa of ornithopod dinosaurs. A collection of extant crocodiles and birds allows more points of comparison. Some endocasts made on the fossil specimens confirmed previously described characteristics, while new ones were brought to our attention. The endocasts opened up not only the morphology of the brain, but also the anatomy of the cranial nerves, the pituitary gland and the presence of valleculae. This last element, evidence of a developped telencephalon, has been established in a new Hadrosauroidea species as his oldest occurrence. The brain of more derived Ornithopods was characterized by very large cerebral hemispheres. The pontine and cranial flexures disappeared, to the contrary to what is observed in Saurischians. The olfactory peduncles were large. New evidences about the correlation between the size of the pituitary gland and the size of the individual. The Ornithopod’s brain changed throughout their evolution :the most striking is the increase of the cerebral hemispheres. The complexity of behaviors exhibited by Ornithopods is suggested as the trigger of the increase of the size of the cerebral hemispheres.

A new phylogenetic analysis was established, including new characters from the endocranial cavity. It brings interesting perspectives about the position of several basal Iguanodontia. Unfortunately the resolution is weak and new studies will be needed. The relationships are not stable and small changes lead to instabilities in the result of the phylogenetic analysis.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2013
A thorough description and cladistic analysis of the Antetonitrus ingenipes type material sheds further light on the stepwise acquisition of sauropodan traits just prior to the Triassic/Jurassic boundary. Although the forelimb of Antetonitrus and other closely related sauropododomorph taxa retains the plesiomorphic morphology typical of a mobile grasping structure, the changes in the weight-bearing dynamics of both the musculature and the architecture of the hindlimb document the progressive shift towards a sauropodan form of graviportal locomotion. Nonetheless, the presence of hypertrophied muscle attachment sites in Antetonitrus suggests the retention of an intermediary form of facultative bipedality. The term Sauropodiformes is adopted here and given a novel definition intended to capture those transitional sauropodomorph taxa occupying a contiguous position on the pectinate line towards Sauropoda. The early record of sauropod diversification and evolution is re-examined in light of the paraphyletic consensus that has emerged regarding the ‘Prosauropoda’ in recent years.

Diplodocidae are among the best known sauropod dinosaurs. Several species were described in the late 1800s or early 1900s. Since then, numerous additional specimens were recovered in the USA, Tanzania, Portugal, as well as possibly Spain, England, and Asia. To date, the clade includes about 12 to 15 different species, some of them with questionable taxonomic status (e.g. ‘Diplodocus’ hayi or Dyslocosaurus polyonychius). However, intrageneric relationships of the multi-species, iconic genera Apatosaurus and Diplodocus are still poorly known. The way to resolve this issue is a specimen-based phylogenetic analysis, which was done for Apatosaurus, but is here performed for the first time for the entire clade of Diplodocidae. New material from different localities and stratigraphic levels on the Howe Ranch (Shell,Wyoming, USA) sheds additional light on the evolution of Diplodocidae. Three new specimens are described herein, considerably increasing our knowledge of the anatomy of the group. The new specimens (SMA 0004, SMA 0011, and SMA 0087) represent two, to possibly three new diplodocid species. They preserve material from all parts of the skeleton, including two nearly complete skulls, as well as fairly complete manus and pedes, material which is generally rare in diplodocids. Thereby, they considerably increase anatomical overlap between the sometimes fragmentary holotype specimens of the earlier described diplodocid species, allowing for significant results in a specimenbased phylogenetic analysis. Furthermore, clavicles and interclavicles are identified, the latter for the first time in dinosaurs. Their presence seems restricted to early sauropods, flagellicaudatans, and early Macronaria, and might thus be a retained plesiomorphy, with the loss of these bones being synapomorphic for Titanosauriformes and possibly Rebbachisauridae. The new material allows to test previous hypotheses of diplodocid phylogeny. In order to do so, any type specimen previously proposed to belong to Diplodocidae was included in the study, as are relatively complete referred specimens, in order to increase the degree of overlapping material. For specimens subsequently suggested to be non-diplodocid sauropods, their hypothesized sister taxa were included as outgroups. The current phylogenetic analysis thus includes 76 operational taxonomic units, 45 of which belong to Diplodocidae. The specimens were scored for 477 morphological characters, representing one of the most extensive phylogenetic analyses done within sauropod dinosaurs. The resulting cladogram recovers the classical arrangement of diplodocid relationships. Basing on a newly developed numerical approach to reduce subjectivity in the decision of specific or generic separation, species that have historically been included into well-known genera like Apatosaurus or Diplodocus, were detected to be actually generically different. Thereby, the famous genus Brontosaurus is resuscitated, and evidence further suggests that also Elosaurus parvus (previously referred to Apatosaurus) or ‘Diplodocus’ hayi represent unique genera. The study increases our knowledge about individual variation, and helps to decide how to score multi-species genera. Such a specimen-based phylogenetic analysis thus proves a valuable tool to validate historic species in sauropods, and in paleontology as a whole.
Fundação para a Ciência e a Tecnologia - (SFRH / BD / 66209 / 2009)

Troodontidae is an important dinosaur taxon that closely resembles birds in both morphology and biology. The evolution of troodontids is crucial for understanding evolutionary transitions between non-avialan theropods and avialans. Despite the recent discovery of several troodontid taxa across the world and many new studies of coelurosaurian relationships, an overall survey of morphological variation in troodontids and a comprehensive analysis of ingroup troodontid relationships have yet to be accomplished. In the first four chapters of this dissertation, the osteology of two new troodontid taxa and two closely related paravians are described in detail. These descriptions are based on new specimens recovered from the Mesozoic of China and Mongolia. These new taxa include the basal dromaeosaurid Microraptor zhaoianus, the basal avialan Anchiornis huxleyi, a new troodontid taxon represented by IGM 100/1323, and a second new troodontid taxon represented by IGM 100/1126 and IGM 100/3500. These paravian taxa are all small-sized, with a basal paravian body plan resembling Archaeopteryx, yet they represent members of all three major paravian lineages (Troodontidae, Dromaeosauridae and Avialae), and support the traditionally recognized paravian interrelationships. Osteological description of Microraptor zhaoianus is based on an excellently preserved new specimen BMNHC PH881. This specimen preserves significant morphological details that are not present, or are poorly preserved, in the other Microraptor specimens, including aspects of the skull, rib cage, and humerus. These new characters corroborate Microraptor as a member of the Dromaeosauridae and support the close relationship of troodontids with dromaeosaurids. Four new specimens (PKUVP 1068; BMNHC PH804, BMNHC PH822 and BMNHC PH823) of Anchiornis huxleyi reveal new osteological details of this important paravian taxon. Anchiornis huxleyi shares derived features with avialans, but it lacks derived deinonychosaurian characteristics such as a laterally exposed splenial and a specialized raptorial pedal digit II. IGM 100/1323 represents a new troodontid taxon from the Late Cretaceous Djadokhta Formation of Mongolia, diagnosed from other troodontids by the absence of the lateral groove on the dentary, a posteriorly curved pterygoid flange, a distinct spike-like process on the ischium, and elongate chevrons. Despite generally having a basal paravian body plan, IGM 100/1323 displays many derived troodontid features. IGM 100/1126 and IGM 100/3500 represent another new Late Cretaceous troodontid taxon from the Djadokhta-Formation-like rocks at Ukhaa Tolgod, Mongolia. It is unique and distinct from other troodontids in having closely packed peg-like teeth, a twisted suborbital process of the jugal, a quadratojugal with a crescentic ascending process that braces the quadrate posteriorly, reduction of the basal tubera, and presence of a posterior fossa on the proximal fibula. This new taxon is morphologically more derived than Early Cretaceous troodontids but is more primitive than other Late Cretaceous troodontids. A new and comprehensive phylogenetic analysis of coelurosaurian theropods, focusing on troodontids is presented in Chapter 5. This is an updated version of the Theropod Working Group (TWiG) analysis (2015.1). This new analysis incorporates new paravian taxa and new characters, most of which are relevant to paravians, especially the troodontids that are the focus of this dissertation. The new phylogenetic analysis agrees with previous studies on the general relationships of coelurosaurians, yet some important differences from previous TWiG analyses are present in paravians, including: 1), the Jianchang paravians are recovered as basal avialans; 2), Late Cretaceous troodontids form a monophyletic group; and 3), Jinfengopteryginae is not monophyletic.

Theropod dinosaurs are an iconic and familiar group of extinct species that include predators such as Tyrannosaurus and Velociraptor, as well as an array of other Mesozoic taxa. Carnivorous theropods are the evolutionary ancestors of birds, and the evolutionary transition between theropods and birds is a textbook example of a major evolutionary transformation in the history of life. Despite a flurry of research on early birds and their dinosaurian relatives, however, several questions still remain. First, the anatomy of some major theropod groups has yet to be described in detail. Second, there is little consensus on the phylogenetic relationships of the basal members of a theropod subgroup called Coelurosauria: the clade of birds and their closest relatives (defined as all taxa closer to birds than to Allosaurus). Third, there has been little synthetic work on large-scale macroevolutionary patterns during theropod evolution. This dissertation includes three chapters that touches on these three major issues. Chapter 1 is a detailed description of the Late Cretaceous tyrannosaurid theropod Alioramus altai, based on its holotype specimen from the Tsaagan Khuushu locality in the Maastrichtian Nemegt Formation of Mongolia. This monographic description provides further evidence that Alioramus is an unusual long-snouted, gracile, and slender-limbed taxon with an unpredecented degree of cranial ornamentation among tyrannosaurids and an extremely pneumatized skeleton. Anatomical comparisons indicate that the long skull of Alioramus is an autapomorphic feature that is proportionally longer (relative to femur length) than in any other known tyrannosaurid specimen, including juveniles, and that Alioramus is morphologically distinctive relative to similarly-sized individuals of the contemporary and sympatric Tarbosaurus. The coexistence of the long-snouted Alioramus and robust and deep-snouted Tarbosaurus, which are found together at the Tsaagan Khuushu locality, demonstrate that multiple large tyrannosaurids were able to live in sympatry, likely because of niche partitioning due to differences in craniofacial morphology and functional behavior. Chapter 2 presents a comprehensive new phylogenetic analysis of coelurosaurian theropods, which is an updated version (and thus the latest iteration) of the long-standing Theropod Working Group (TWiG) analysis. The new analysis incoroporates a wealth of new taxa and character data into the TWiG matrix for the first time, most of which is relevant to basal (non-maniraptoran) coelurosaurs such as tyrannosauroids and ornithomimosaurs, which had previously been the subject of only cursory character and taxon sampling in TWiG studies. The full dataset was analyzed under parsimony, and the resulting phylogeny includes several well supported relationships and agrees with previous analyses in many aspects. As a result, it is argued that a consensus view of basal coelurosaurian relationships has emerged, including: 1) the monophyly of major subclades such as Tyrannosauroidea, Compsognathidae, and Ornithomimosauria; 2) the position of the singleton genera Bicentenaria, Zuolong, and Tugulusaurus near the base of Coelurosauria; 3) the placement of Tyrannosauroidea as the most basal major coelurosaurian subclade; 4) the inclusion of Guanlong, Dilong, and Proceratosaurus within Tyrannosauroidea; 5) the existence of a derived maniraptoran clade that includes alvarezsauroids, therizinosauroids, oviraptorosaurs, and paravians to the exclusion of ornithomimosaurs and tyrannosauroids. Remaining areas of uncertainty include the phylogenetic position of Compsognathidae and the singleton genus Ornitholestes, and relationships at the base of the Ornithomimosauria + Maniraptora clade and Maniraptora itself. The phylogeny indicates that much of the early history of Coelurosauria has yet to be sampled in the fossil record, that coelurosaurs originated at small body size, and that the evolution of the iconic Tyrannosaurus-like bauplan occurred only towards the end of the Cretaceous. Chapter 3 presents a geometric morphometric analysis that is used to study broad patterns in theropod skull shape variation and compare the distribution of taxa in cranial morphospace (form) to both phylogeny and quantitative metrics of biting behaviour (function). The analysis finds that theropod skulls primarily differ in relative anteroposterior length and snout depth and to a lesser extent in orbit size and depth of the cheek region, and that oviraptorosaurs deviate most strongly from the "typical" and ancestral theropod morphologies. Noncarnivorous taxa generally fall out in distinct regions of morphospace and exhibit greater overall disparity than carnivorous taxa, whereas large-bodied carnivores independently converge on the same region of morphospace. The distribution of taxa in morphospace is strongly correlated with phylogeny but only weakly correlated with functional biting behaviour. These results imply that phylogeny, not biting function, was the major determinant of theropod skull shape.