| With the goal of elucidating the evolutionary history of hadrosaurids, I present the most comprehensive and resolved phylogeny of these animals ever estimated, using a complete taxonomic sampling at specific level. I also report the results of a biogeographic analysis seeking to establish the ancestral area of Hadrosauridae, testing whether they originated in Asia, North or South America. In addition I used the same method to track their diversification in relation to intercontinental connections throughout their tenure.;Parsimony and Bayesian methods were implemented to elucidate the phylogenetic relationships of all hadrosaurid species. Continuous geometries were studied using the Analysis of Planar Shapes Using Geodesic Paths, a novel landmark-free method that considers the continuous non-linear geometry of the bones. In this way, a total of 299 phylogenetically informative characters (205 cranial and 94 postcranial) were defined and documented, the most extensive character data set ever constructed for hadrosaurid dinosaurs.;In general, parsimony and Bayesian analyses confirmed the dichotomic evolution of hadrosaurids into Saurolophinae and the hollow-crested Lambeosaurinae. The hadrosaurid radiation and the divergence of saurolophines from lambeosaurines occurred no later than the Santonian and was coincident with the evolution of a suite of mandibular characters (i.e., increased number of tooth families, presence of three teeth forming the dentary occlusal plane, ventral offset of the oral predentary-premaxilla contact). These characters may have been key innovations. These results suggest that feeding adaptations might have played a central role in the diversification of hadrosaurids. Circumnarial fossae and cranial crests evolved prior to the hadrosaurid radiation. Both of these characters were reconstructed to have evolved at the same time.;Ancestral areas were reconstructed on the phylogeny derived from the weighted parsimony analysis of Hadrosauridae. Fitch parsimony and the Dispersal-Vicariance (DIVA) method were implemented to reconstruct ancestral areas for all clades of Hadrosauria. The results show that the genesis of Hadrosauridae occurred in eastern North America during the late Santonian. Soon after their origin, hadrosaurids dispersed to Asia, the ancestral area for the major Saurolophinae-Lambeosaurinae divergence. Vicariant events may have occurred following several of the inferred hadrosaurid dispersals. Thus, both vicariance and dispersal may have been instrumental in shaping the recorded distribution of hadrosaurids.;Here, I provide a revised and complete osteology of the type specimens and hypodigms for the only two taxa known from South America, Secernosaurus koerneri and Kritosaurus australis. K. australis is regarded as a junior synonym of S. koerneri, based on a combination of iliac and pubic characters unique to these two taxa. Inclusion of S. koerneri within the genus Kritosaurus is not supported by the phylogenetic analysis. S. koerneri is inferred to be a member of the "kritosaur" clade within Saurolophinae, as the sister taxon to the Argentinean OTU from Salitral Moreno.;Finally, an regarding European hadrosaurids, the observation of previously unrecognized characters in the maxilla and dentary of Tsintaosaurus spinorhinus (Campanian of China) and Pararhabdodon isonensis (Maastrichtian of Spain) led to a revision of the taxonomy and phylogenetic relationships of the latter. In particular, the extreme elongation of the symphyseal region of the type and only material of Koutalisaurus kohlerorum (a dentary from the Maastrichtian of Spain) was also observed in T. spinorhinus. This implied that K. kohlerorum is indistinct from T. spinorhinus. This, in combination with the fact that P. isonensis and T. spinorhinus share a maxilla with elevated jugal joint continuous with the ectopterygoid ridge (a character not seen among Iguanodontoidea), led me to the conclusion that K. kohlerorum as a junior synonym of P. isonensis . The incorporation of those new characters in Bayesian and parsimony phylogenetic analyses of Hadrosauridae resulted in the inference that Pararhabdodon isonensis and Tsintaosaurus spinorhinus form a clade of basal lambeosaurines---the "tsintaosaurs". (Abstract shortened by UMI.)... |
