Prosaurolophus maximus is a crested hadrosaurine known from numerous specimens from the Dinosaur Park Formation of Alberta. Therefore, it is an ideal taxon to reconstruct patterns of growth and variation in hadrosaurids, and improve our understanding of their evolutionary relationships. This study describes the cranial anatomy of P. maximus, quantitatively examines its range of variation, and provides the first ontogenetic series for this taxon. A second species, P. blackfeetensis, was named based on morphological differences in the characteristic nasal crest; however, morphometric results fail to quantitatively differentiate P. blackfeetensis from P. maximus. A species-level phylogenetic analysis of hadrosaurids recovers P. maximus and P. blackfeetensis as sister taxa. Based on both the morphometric and phylogenetic data, this study supports the previous hypothesis that P. blackfeetensis is a junior synonym of P. maximus thereby substantially increasing its temporal range, and suggests a long period of morphological stasis in this taxon.

Prosaurolophus maximus is a crested hadrosaurine known from numerous specimens from the Dinosaur Park Formation of Alberta. Therefore, it is an ideal taxon to reconstruct patterns of growth and variation in hadrosaurids, and improve our understanding of their evolutionary relationships. This study describes the cranial anatomy of P. maximus, quantitatively examines its range of variation, and provides the first ontogenetic series for this taxon. A second species, P. blackfeetensis, was named based on morphological differences in the characteristic nasal crest; however, morphometric results fail to quantitatively differentiate P. blackfeetensis from P. maximus. A species-level phylogenetic analysis of hadrosaurids recovers P. maximus and P. blackfeetensis as sister taxa. Based on both the morphometric and phylogenetic data, this study supports the previous hypothesis that P. blackfeetensis is a junior synonym of P. maximus thereby substantially increasing its temporal range, and suggests a long period of morphological stasis in this taxon.

Aetosaurians are a clade of pseudosuchian archosaurs that were globally dispersed during the Late Triassic Epoch. Aetosaurians are characterized by a suite of osteoderms that covered much of the body. These osteoderms are commonly recovered as fossils and possess characteristic surface ornamentation that can be diagnostic for taxa. The abundance of these osteoderms and the ease of identification have made aetosaurians ideal index taxa for Late Triassic biostratigraphy. Of special interest are specimens from South and North America and Europe that have been assigned to the genus Stagonolepis, which have been utilized for correlation of continental sedimentary units and to approximately date the timing of important biotic events. New finds have called the synonymy of these Stagonolepis-like specimens into question, jeopardizing their ability to serve as biochronological markers. Detailed examination of all of the specimens assigned to Stagonolepis robertsoni demonstrates that all of these specimens do not represent the same species. The South American material is assigned to the genera Aetosauroides, Aetobarbakinoides, and Polesinesuchus; the European material to Stagonolepis; and the North American material to Calyptosuchus, Adamanasuchus, and a newly recognized taxon, Scutarx deltatylus. Scutarx deltatylus can be differentiated from other aetosaurians by the presence of a strongly raised, triangular boss, on the posteromedial corner of the paramedian osteoderms. Scutarx deltatylus also preserves the first good skull material from a Stagonolepis-like aetosaur from North America. A dorsoventrally thickened skull roof and an anteroposteriorly short parabasisphenoid further demonstrate the distinctness of this material from that of South America and Europe. A detailed phylogenetic analysis of all known aetosaurians further demonstrates the distinctness of these taxa. This new expanded analysis of 28 taxa and 83 characters recovers Aetosauroides scagliai as the sister taxon to all other aetosaurians. Stagonolepis robertsoni from Scotland does not clade with Stagonolepis olenkae from Poland. Calyptosuchus wellesi is the sister taxon to a clade consisting of Scutarx deltatylus and Adamanasuchus eisenhardtae. However, distribution of autapomorphies across these taxa precludes them from being synonymized. As a result the Stagonolepis-like aetosaurs cannot be used for global scale correlations of Upper Triassic strata, but do appear to be of utility for regional correlations, in particular those between the Chinle Formation and Dockum Group in the American Southwest. / text

The Triassic Period (~252–201.5 Ma) saw a transformative radiation and reorganization of continental tetrapod diversity following the end-Permian Extinction, including an assemblage of diverse forms that do not survive the end-Triassic (herein termed the 'endemic Triassic fauna', =ETF), as well as the earliest fossil representatives of all major modern tetrapod groups (herein termed the 'Living [Triassic to Recent] Fauna', =LTF; i.e. Salientia, Caudata, Gymnophiona, Mammaliaformes, Squamata, Rhynchocephalia, Testudinata, Crocodylomorpha, and Dinosauria). With few exceptions, only the LTF assemblage survives the end-Triassic Extinction (~201.5 Ma), highlighting the Late Triassic (~227–201.5 Ma) record as essential for understanding this pivotal transition and the evolutionary and ecological origins of post-Triassic non-marine tetrapod faunas, including those of present day. Micro-microvertebrate bonebeds are arguably the best proxy for tracking continental vertebrate biodiversity, however gaps in their Late Triassic record obscure patterns and drivers of evolutionary, ecological, and environmental change during the rise of LTF communities. In my dissertation, I use new data collected from Upper Triassic microvertebrate bonebeds from North America, and particularly the Thunderstorm Ridge site (PFV 456) in Petrified Forest National Park, Arizona, U.S.A, to fill gaps in the evolutionary record of specific groups (e.g., lissamphibians and lepidosaurs), as well as the vertebrate paleocommunity record of Triassic equatorial Pangaea. My first chapter describes and analyzes an assemblage of gymnophionomorph (stem caecilian) bones from PFV 456 which represent the oldest-known caecilian fossils globally. As the oldest caecilian fossils, they provide new support for the dissorophoid temnospondyl affinities of caecilians and other living amphibians, evidence of a step-wise acquisition of caecilian anatomies associated with fossoriality, and evidence of an ancient pattern of equatorial biogeographic restriction in caecilians from the Triassic to the present day. My second chapter describes and analyzes an assemblage of lepidosauromorphs from the Late Triassic of Equatorial Pangaea, providing new insights into the step-wise evolution tooth and jaw morphologies near the divergence of living lepidosaur clades (Squamata and Rhynchocephalia), and showing evidence for the Triassic acquisition in stem squamates and non-squamate lepidosaurs of dental features conserved in living squamates. The third chapter uses apomorphy-based identifications to describe the vertebrate diversity of the Thunderstorm Ridge site (PFV 456), providing evidence for the most species rich continental vertebrate community yet-known from the Triassic, with 55 vertebrate taxa. Nearly all LTF clades are present, predating similar assemblages from the early Jurassic by over 20 million years, and indicating that the assembly of the first LTF communities by at least 220 million years ago, long before the Triassic-Jurassic Extinction event (~201.5). The presence of this exceptional diversity may be linked to the climatic and environmental settings of equatorial Pangaea during the Triassic. / Doctor of Philosophy / The Triassic Period, lasting about 50 million years from approximately 252 to 201.5 million years ago, was a period of transformation for life living on land. During the Triassic, we see the first fossil evidence for the evolution of the tetrapod (animals with a backbone and limbs) groups familiar to us from the present-day Earth, including frogs, salamanders, caecilians, mammals, lizards, the tuatara, turtles, crocodilians, and dinosaurs. Understanding the early evolution of these groups is limited by gaps in the Triassic fossil record, particularly for groups with small-bodies and delicate skeletons like frogs, salamanders, caecilians, and lizards. The poor Triassic records of these groups also limits understandings of when and where tetrapod communities resembling those of the present-day first assembled, and whether events like the Triassic-Jurassic Extinction event (~201.5 million years ago) shaped the organization of these communities. To fill these gaps, I have focused on collecting data from microvertebrate bonebeds, layers of rock that preserve the small, delicate bones of small-bodied vertebrates that are typically rare elsewhere. New microvertebrate data collected from Late Triassic rocks in North America, and particularly the 220 million year old Thunderstorm Ridge site (PFV 456) in Petrified Forest National Park, Arizona, U.S.A., provide evidence for exceptionally diverse tetrapod communities, opening a window onto the early evolution of living tetrapods and their ecological interactions. In my first chapter I describe and analyze the bones of a stem caecilian amphibian from the Thunderstorm Ridge site. These are the oldest caecilian fossils on Earth, and they provide new evidence for the evolutionary relationships, ecologies, and biogeography of these enigmatic living amphibians. In my second chapter I describe and analyze the jaws and teeth of early lizards and their close relatives from North American Late Triassic microvertebrate sites, showing that the tooth and jaw morphologies of living lizards like geckos and skinks first evolved in their Triassic relatives. In my third chapter, I describe and identify the 55 vertebrate taxa recovered from the Thunderstorm Ridge site, showing that it is the most diverse tetrapod community known from the Triassic. The diversity of early members of living tetrapod groups at Thunderstorm Ridge suggests that tetrapod communities resembling those of the present-day first assembled in the Triassic, at least 20 million years prior to the Triassic-Jurassic Extinction.

Vertebrate fossils have been discovered at several locations in the Bighorn Basin (Wyoming). The Virginia Museum of Natural History's (VMNH) digsite is located in the eastern part of the Bighorn Basin, in the Coyote Basin. Many scientists have worked within these basins trying to describe the stratigraphy. One question specifically asked is where the boundary between the Morrison Fm. (Jurassic) and the Cloverly Fm. (Cretaceous) lies. This new study attempted to show if the current method (Kvale, 1986) of determining the boundary is appropriate. The stratigraphy of the area was examined using Kvale, 1986, Ostrom, 1970, and Moberly, 1960's work in order to see which model was more robust. The fossils in the VMNH digsite were used to supplement the stratigraphic data in determining the age of specific beds. All of Ostrom's units were identified throughout the study area. There is some doubt as to whether the units would be acceptable outside of the Coyote Basin because of laterally discontinuity. Nevertheless, his description of units is satisfactory for the study area, and is more appropriate than other methods. The geologic age of the dinosaurs uncovered in the VMNH quarry is in agreement with the age determined stratigraphically. The VMNH site is below Ostrom's Unit II, which would place it in the Late Jurassic. The determination of the Jurassic/Cretaceous stratigraphic boundary has not been resolved. However, since the Pryor Conglomerate member of the Cloverly Fm. can be identified throughout this area, it is proposed as the Morrison Fm./Cloverly Fm. boundary. / Master of Science

Mourasuchus (Alligatoroidea, Caimaninae) é um táxon extinto de crocodilianos restrito ao Cenozoico da América do Sul. Representa um dos grupos de crocodilianos mais peculiares de todos os tempos, devido ao formato longo, largo e achatado de seu rostro (lembrando o bico de um pato) entre outras características. Apesar dessas peculiaridades, relativamente poucos trabalhos foram feitos sobre esse grupo. A maioria das descrições morfológicas dos fósseis do gênero são sucintas e breves, incluindo as dos holótipos de duas das quatro espécies a ele assinaladas: M. amazonensis e M. arendsi. Do mesmo modo, as diagnoses das quatro espécies também se mostram sucintas. Poucas também são as análises filogenéticas realizadas com Mourasuchus a maioria das quais, porém, recupera Orthogenysuchus olseni, do Eoceno dos Estados Unidos, como táxon-irmão de Mourasuchus, gerando um impasse biogeográfico. Além disso, a maneira exata pela qual Mourasuchus se alimentava, fazendo uso de seu peculiar rostro bico de pato, bem como seus itens alimentares, ainda não foram plenamente esclarecidos, ainda que algumas teorias tenham sido propostas na literatura. Assim, este trabalho se propôs a: oferecer uma re-descrição dos holótipos de M. amazonensis e M. arendsi; revisar as diagnoses das espécies e do próprio gênero; realizar uma análise filogenética investigando as relações das espécies entre si e do gênero, como um todo, em Caimaninae; investigar a relação de Orthogenysuchus olseni como táxon-irmão de Mourasuchus; elucidar o modo de forrageio e os itens alimentares consumidos pelo grupo. As re-análises das diagnoses das espécies revelaram que duas delas constituem, na verdade, espécies não-válidas, enquanto a análise de um novo material craniano descrito neste trabalho (MCNC-PAL-110-72V) revelou a existência de uma nova espécie de Mourasuchus, fazendo com que este trabalho reconheça três espécies válidas para o gênero. A análise filogenética revelou M. atopus como o táxon mais basal, enquanto M. amazonensis e a nova espécie proposta formam um clado mais derivado. Orthogenysuchus olseni não foi recuperado como táxon-irmão de Mourasuchus em nenhuma das análises, mas seu posicionamento ainda dentro de Caimaninae faz com que impasses biogeográficos permaneçam. Este trabalho defende que Mourasuchus coletava presas em grande quantidade usando a musculatura da parte de baixo de seu rostro uma alimentação coletora enquanto ainda não há evidências de que esses animais fariam uma filtração da massa alimentar coletada. É possível, também, que tal hábito tenha evoluído a partir do hábito alimentar durófago exibido por Caimaninae basais, especialmente o gênero Gnatosuchus. / Mourasuchus (Alligatoroidea, Caimaninae) is an extinct crocodilian taxon restricted to the Cenozoic of South America. It represents one of the most peculiar crocodilian groups of all time, due to the long, wide, flattened shape of its rostrum (resembling the beak of a duck), among other features. Regardless these peculiarities, relatively few works have been done about this group. Most of morphological descriptions of the fossils belonging to this genus are shot and brief, including those of two from the four species assigned to it: M. amazonensis and M. arendsi. Similarly, the diagnoses of all the four species are also very brief. The phylogenetic analyses involving Mourasuchus are also very few most of them, however, recover Orthogenysuchus olseni, from the Eocene of the United States, as Mourasuchus sister-taxon, creating a biogeographically problematic scenario. Furthermore, the exact way by which Mourasuchus feed itself, using its peculiar beak of duck rostrum, as well as its prey items, are yet to be determined, even though some proposals have already been made in the literature. As such, this work had the following objectives: offer a redescription of the holotypes of M. amazonensis and M. arendsi; re-evaluate the diagnoses of Mourasuchus species and the genus itself; perform a phylogenetic analysis to evaluate the relationships between Mourasuchus species and of this group, as a whole, within Caimaninae; evaluate the position of Orthogenysuchus olseni as a sister-taxon of Mourasuchus; elucidate the foraging tactics and the prey items consumed by this group. The re-evaluation of the diagnoses of the species revealed that two are in reality non-valid species, while the analysis of a new cranial material described in this work (MCNC-PAL-110-72V) revealed the existence of a new species of Mourasuchus, taking this work to recognize the existence of three valid species for the genus. The phylogenetic analysis recovered M. atopus as the basalmost taxon, while M. amazonensis and the new species proposed in this work form a more derived clade. Orthogenysuchus olseni was not recovered as a Mourasuchus sister-taxon in any of the analyses made, but its position still within Caimaninae maintains biogeographically problematic scenarios in this clade. This work defends that Mourasuchus collected a high number of prey items using the musculature between the lower jaws a collecting foraging tactic while there is still no evidence that these animals could perform a straining of the entire concentration of food it collected. It is possible, as well, that such habit may have evolved from the durophagous feeding habit of some basal Caimaninae, especially Gnatosuchus.

Birds are the most diverse extant group of terrestrial vertebrates, and relationships amongst major extant and extinct avian lineages remain hotly debated. A clade of Aves which has received limited attention is the extinct Zygodactylidae, a species-rich group of perching birds that possess a foot with a retroverted fourth toe, an elongate tarsometatarsus and a large intermetacarpal process in the wing. Specimens currently included within Zygodactylidae previously were thought to be sister taxa to songbirds (Passeriformes) or woodpeckers and allies (Piciformes). Zygodactylids were most abundant during the Eocene in North America and Europe and persisted to the Early Miocene. Five exceptionally preserved fossils from the Early Eocene Green River Formation of Wyoming are described, and provide insights into the interrelationships of zygodactylid taxa and the position of the clade within Aves. In an attempt to resolve systematic relationships within zygodactylids, and the position of the clade within Aves, I conducted two sets of phylogenetic analyses. The first focused on clarifying relationships within Zygodactylidae. Each taxon was evaluated for 37 morphological characters. Resulting strict consensus cladograms yield topologies in which two of the new Green River specimens are positioned in a clade within Zygodactylus, a taxon previously known only from the Early Oligocene and Early Miocene of Europe. The second set of analyses sought to assess which extant avian lineage is most closely allied with Zygodactylidae. Those analyses used a dataset of 135 characters evaluated for 57 species and a supraspecific terminal, Zygodactylidae. Scoring of Zygodactylidae was based on morphological observations from all described taxa within Zygodactylidae. The extant species sample was chosen to evaluate previously proposed hypotheses of relationships between Zygodactylidae and other avian clades and included songbirds, parrots and 43 species from the coraciiform-piciform clade (e.g., woodpeckers, galbulids, rollers and motmots). Outgroup species were iteratively swapped to determine if outgroup choice affected recovered estimates of zygodactylid relationships within Aves. Zygodactylidae is the sister taxon to songbirds in the resultant tree topologies. These results forward our understanding of the relationship between Zygodactylidae and Passeriformes within Aves. / text

Mourasuchus (Alligatoroidea, Caimaninae) é um táxon extinto de crocodilianos restrito ao Cenozoico da América do Sul. Representa um dos grupos de crocodilianos mais peculiares de todos os tempos, devido ao formato longo, largo e achatado de seu rostro (lembrando o bico de um pato) entre outras características. Apesar dessas peculiaridades, relativamente poucos trabalhos foram feitos sobre esse grupo. A maioria das descrições morfológicas dos fósseis do gênero são sucintas e breves, incluindo as dos holótipos de duas das quatro espécies a ele assinaladas: M. amazonensis e M. arendsi. Do mesmo modo, as diagnoses das quatro espécies também se mostram sucintas. Poucas também são as análises filogenéticas realizadas com Mourasuchus a maioria das quais, porém, recupera Orthogenysuchus olseni, do Eoceno dos Estados Unidos, como táxon-irmão de Mourasuchus, gerando um impasse biogeográfico. Além disso, a maneira exata pela qual Mourasuchus se alimentava, fazendo uso de seu peculiar rostro bico de pato, bem como seus itens alimentares, ainda não foram plenamente esclarecidos, ainda que algumas teorias tenham sido propostas na literatura. Assim, este trabalho se propôs a: oferecer uma re-descrição dos holótipos de M. amazonensis e M. arendsi; revisar as diagnoses das espécies e do próprio gênero; realizar uma análise filogenética investigando as relações das espécies entre si e do gênero, como um todo, em Caimaninae; investigar a relação de Orthogenysuchus olseni como táxon-irmão de Mourasuchus; elucidar o modo de forrageio e os itens alimentares consumidos pelo grupo. As re-análises das diagnoses das espécies revelaram que duas delas constituem, na verdade, espécies não-válidas, enquanto a análise de um novo material craniano descrito neste trabalho (MCNC-PAL-110-72V) revelou a existência de uma nova espécie de Mourasuchus, fazendo com que este trabalho reconheça três espécies válidas para o gênero. A análise filogenética revelou M. atopus como o táxon mais basal, enquanto M. amazonensis e a nova espécie proposta formam um clado mais derivado. Orthogenysuchus olseni não foi recuperado como táxon-irmão de Mourasuchus em nenhuma das análises, mas seu posicionamento ainda dentro de Caimaninae faz com que impasses biogeográficos permaneçam. Este trabalho defende que Mourasuchus coletava presas em grande quantidade usando a musculatura da parte de baixo de seu rostro uma alimentação coletora enquanto ainda não há evidências de que esses animais fariam uma filtração da massa alimentar coletada. É possível, também, que tal hábito tenha evoluído a partir do hábito alimentar durófago exibido por Caimaninae basais, especialmente o gênero Gnatosuchus. / Mourasuchus (Alligatoroidea, Caimaninae) is an extinct crocodilian taxon restricted to the Cenozoic of South America. It represents one of the most peculiar crocodilian groups of all time, due to the long, wide, flattened shape of its rostrum (resembling the beak of a duck), among other features. Regardless these peculiarities, relatively few works have been done about this group. Most of morphological descriptions of the fossils belonging to this genus are shot and brief, including those of two from the four species assigned to it: M. amazonensis and M. arendsi. Similarly, the diagnoses of all the four species are also very brief. The phylogenetic analyses involving Mourasuchus are also very few most of them, however, recover Orthogenysuchus olseni, from the Eocene of the United States, as Mourasuchus sister-taxon, creating a biogeographically problematic scenario. Furthermore, the exact way by which Mourasuchus feed itself, using its peculiar beak of duck rostrum, as well as its prey items, are yet to be determined, even though some proposals have already been made in the literature. As such, this work had the following objectives: offer a redescription of the holotypes of M. amazonensis and M. arendsi; re-evaluate the diagnoses of Mourasuchus species and the genus itself; perform a phylogenetic analysis to evaluate the relationships between Mourasuchus species and of this group, as a whole, within Caimaninae; evaluate the position of Orthogenysuchus olseni as a sister-taxon of Mourasuchus; elucidate the foraging tactics and the prey items consumed by this group. The re-evaluation of the diagnoses of the species revealed that two are in reality non-valid species, while the analysis of a new cranial material described in this work (MCNC-PAL-110-72V) revealed the existence of a new species of Mourasuchus, taking this work to recognize the existence of three valid species for the genus. The phylogenetic analysis recovered M. atopus as the basalmost taxon, while M. amazonensis and the new species proposed in this work form a more derived clade. Orthogenysuchus olseni was not recovered as a Mourasuchus sister-taxon in any of the analyses made, but its position still within Caimaninae maintains biogeographically problematic scenarios in this clade. This work defends that Mourasuchus collected a high number of prey items using the musculature between the lower jaws a collecting foraging tactic while there is still no evidence that these animals could perform a straining of the entire concentration of food it collected. It is possible, as well, that such habit may have evolved from the durophagous feeding habit of some basal Caimaninae, especially Gnatosuchus.

No description available.

No description available.