Type of Document Dissertation Author Prieto-Marquez, Albert Author's Email Address email@example.com URN etd-07102008-102339 Title Phylogeny and Historical Biogeography of Hadrosaurid Dinosaurs Degree Doctor of Philosophy Department Biological Science, Department of Advisory Committee
Advisor Name Title Gregory M. Erickson Committee Chair David L. Swofford Committee Member Fredrik Ronquist Committee Member Scott J. Steppan Committee Member William C. Parker Committee Member Keywords
Date of Defense 2008-06-30 Availability unrestricted AbstractHadrosaurids were the most diverse and abundant dinosaurs at the end of the Cretaceous. However, their phylogeny is incompletely known and the relationships of many taxa, particularly European and South American, remains unresolved. Questions remain regarding the timing of their origin and which attributes might have allowed these animals to diversify and colonize nearly all continents by the late Campanian. Likewise, the center of origin and subsequent biogeographical history of hadrosaurids has remained contentious.
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. These included specimens of 41 hadrosaurids from Europe, Asia and North and South America. Outgroup taxa included twelve iguanodontoidean species from Europe, North America and Asia. New characters were defined and old ones revised on the basis of new data collected from first hand examination of specimens. Traditional and geometric morphometrics were applied to discover patterns of variation containing phylogenetic information. 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. Saurolophines consisted of “saurolophs” and “kritosaurs”. Lambeosaurines consisted of a succession of Eurasian outgroups to two major clades, “parasaurolophs” and “amurosaurs” (“hypacrosaurs” and “corythosaurs”). Hadrosauridae was redefined as the clade stemming from the most recent common ancestor of Hadrosaurus foulkii and Parasaurolophus walkeri. Its monophyly was unambiguously supported by an iliac supraacetabular process that projects lateroventrally between half and three quarters of the dorsoventral depth of the central plate of the ilium and a craniocaudally short supraacetabular process that is less than 55% the length of the central plate of the ilium. The closest outgroup taxa to Hadrosauridae lived in eastern North America. 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. Lambeosaurines and saurolophines dispersed to North America and underwent major cladogenesis during the late Campanian. Within Saurolophinae, “maiasaurs” and “saurolophs” returned to Asia, while “kritosaurs” colonized South America by the late Campanian. Within Lambeosaurinae, “tsintaosaurs” dispersed to Europe no later than the late Campanian. The North American radiations of “hypacrosaurs”, “parasaurolophs” and “corythosaurs” may have represented independent dispersal events from the Asian continent or, alternatively, were part of a single dispersal in the late Campanian with posterior occupations of Asia by a few species from those clades. 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.
Two additional studies were conducted on European and South American hadrosaurids. Although well represented in Asia and North America, the presence of this animals in Europe and South America is known only from rare and fragmentary remains that are poorly documented and mostly unstudied. As a result, the impact of these animals on the phylogenetics and biogeography of hadrosaurids as a whole are not known. 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. Another unnamed hadrosaurid, an OTU from Big Bend National Park, Texas, is positioned as the closest outgroup to the South American clade. The results of this biogeographical analysis indicates that the Secernosaurus clade originated in South America during the late Campanian after a dispersal event (probably followed by vicariance) from southern North America before the end of that geologic stage.
Finally, and 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”. Fitch parsimony and Dispersal-Vicariance reconstruction of ancestral areas on the resulting phylogeny indicated that “tsintaosaurs” originated in eastern Asia during the middle or late Campanian and that P. isonensis represents a dispersal event (followed by vicariance) to Europe that occurred before the end of that geologic stage.
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