Bite marks provide direct evidence of trophic interactions, feeding behavior, and inter- or intraspecific conflict in the fossil record. However, their utility as a source of taphonomic and paleoecologic data requires differentiation from traces left by other processes. Since the 19th century, taphonomists have often relied on actualistic observations of modern bite marks and feeding behaviors in order to identify diagnostic traces and patterns. A recent increase in interest in taphonomic research has resulted in a large body of work describing patterns of bite marks from many different clades. Most research has been focused on mammalian taxa, but a smaller number of non-mammalian groups, including crocodylians, have also drawn interest. Crocodylians are taphonomic agents who consume and modify bones, often depositing them in the active depositional systems in which they live. However, actualistic observations of crocodylian bite marks have been limited to forensic case studies and surveys of two taxa: Crocodylus niloticus and Crocodylus porosus. Both surveys utilized captive animals, which often exhibit atypical morphologies that may bias ensuing bite mark datasets. In order to address this issue, a 2D morphometric analysis of Alligator mississippiensis crania from captive and wild specimens was performed. A principal component analysis and a canonical variates analysis revealed some statistically significant differences between the two groups, while crossvalidation had mixed resuts. An ANCOVA test of the covariance of centroid size and origin against shape (principal component scores) revealed that the effects of ontogeny introduced a stronger signal than captivity. This implies that while using captive crocodylians in fine scale analyses should be avoided, they are suitable for gross scale research, such as bite mark analyses. To explore crocodylian bite mark patterns in greater depth, a large scale survey of traces left by A. mississippiensis was performed. Bite mark types on samples taken from individual feedings were discussed in light of vital statistics and collection protocols. Bite mark types on samples taken from group feedings were classified by location and orientation on bone and type. The results were compared to pre-existing crocodylian datasets with regards to potentially diagnostic traits: bisected marks, hook scores, and a lack of furrows. Bisected marks were found in rates similar to those seen in C. niloticus, and rates of hook scoring and bone breakage were higher. These traces were present in higher rates than those reported in C. porosus. Furrows were identified, but rare. Finally, a survey of bite marks from 21 of the 23 generally recognized species of extant crocodylians was performed to better characterize marks found across Crocodylia and to test methods for synthesizing taphonomic datasets. Bite marks were identified, and specimens were then coded for presence or absence of mark subscores. Attempts to find statistical correlation between mark types, animal vital statistics, and sample collection protocol were unsuccessful. Mapping bite mark character states on a eusuchian phylogeny successfully predicted the presence of bisected marks in previously published, extinct taxa. Predictions for clades that may have created multiple subscores, striated marks, and extensive crushing were also generated. Inclusion of fossil bite marks which have been positively associated with extinct species allow this method to be projected beyond the crown group. The results of this study indicate that phylogenies can and should be explored further for use as predictive tools in a taphonomic framework.

Goniopholididae is a distinctive and common clade of crocodyliforms known from the Jurasic and Cretaceous of Europe, Asia, and North America. Their position within Neosuchia makes them makes them very important to the study of crocodyliform evolution, but unfortunately their phylogenetic status is ambiguous. This study describes the osteology of two North American fossil taxa: Amphicotylus stovalli, a previously under-represented goniopholidid from the Jurassic Morrison Formation of Oklahoma, and new material of Denazinosuchus kirtlandicus from the Cretaceous Kirtland Formation of New Mexico. A phylogenetic dataset is then constructed including a full sampling of Jurassic North American forms and incorporating new new goniopholidid taxa not previously treated in a phylogenetic context. The affinity of North American and European members of Goniopholis is assessed as are the taxonomic status of putitive goniopholidids Vetisuchus and Denazinosuchus. Goniopholididae is monophyletic, and North American goniopholidids form a nested clade united by a distinctive palate morphology. Furthermore, all Morrison Formation goniopholidids are further nested in the North American clade. North American "Goniopholis" are generically distinct from European forms, and should be ascribed to Amphicotylus. Amphicotylus gilmorei is a junior synonym of A. lucasii. Denazinosuchus and Vectisuchus are not constituents of Goniopholididae, and instead are more closely related to pholidosaurs and thalattosuchians.

Ovos fósseis de Crocodyliformes, Aves e Chelonii são artefatos reprodutivos incomuns, conhecidos a partir de registros em poucos países. Tornam-se ainda mais raros quando considerados apenas os achados oriundos de rochas mesozoicas. No Brasil, os registros são limitados à poucos ovos de Crocodyliformes do Cretáceo do Grupo Bauru, bem como um ovo de Chelonii de mesma idade. Desta forma, o presente estudo propôs-se a realizar a descrição de doze ovos fósseis coletados em Campina Verde-MG, e de outros dois provenientes de Álvares Machado e Pirapozinho, região de Presidente Prudente-SP, oriundos de rochas cretáceas (Grupo Bauru). Para tal, utilizou-se técnicas de análises ultraestruturais como Microscopia Eletrônica de Varredura, Espectrometria por Dispersão de Energia e Microscopia Óptica, além de Tomografia Computadorizada para verificar a ocorrência de embriões. Os resultados das análises sugerem a afinidade dos doze ovos de Campina Verde a Crocodyliformes e, pela topotipia do horizonte estratigráfico, a possível associação destes a Pissarrachampsa sera. Adicionalmente, o recorrente registro de ovos fósseis associados a restos esqueletais de crocodilianos notosúquios sugere um nível de cuidado parental presente no grupo. Já o espécime de Álvares Machado possui feições de Enantiornithes. Por fim, o ovo coletado em Pirapozinho possui características semelhantes às de ovos de quelônios Podocnemidae, o único grupo de Chelonii conhecido no afloramento de onde provém o ovo / Amniotes fossil eggs, such as Crocodyliformes, Aves and Chelonii, are known from few places worldwide, and the Mesozoic records are particularly rare. Similarly, the occurrence of eggs of these groups is also rare in Brazil and limited to few crocodylian eggs and a single Chelonii one from Cretaceous rocks. This work aimed to describe twelve fossil eggs collected in Campina Verde-MG, and two additional eggs from Álvares Machado and Pirapozinho, SP, all from Bauru Group rocks (Upper Cretaceous). The ultrastructural traits of the shells were analyzed by Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Optical Microscopy, in addition, Computadorized Tomography was applied to check the embryos occurrence. The twelve eggs from Campina Verde are associated to Crocodyliformes. In addition, the topotipic principle suggests an association of these eggs to the crocodyliform Pissarrachampsa sera. Additionally, the recurrent association of notosuchians fossil eggs and skeletal remains suggests a level of parental care in this group. The specimen from Álvares Machado is associated to Enantiornithes, and the egg from Pirapozinho shares traits with Podocnemidae eggs, which is the only known Chelonii group found in the outcrop where the egg came from

Com 23-24 espécies viventes, a diversidade atual de crocodilianos é irrisória quando comparada ao registro fóssil do grupo, principalmente se considerados todos os representantes de Crocodyliformes. À luz desta grande diversidade, este trabalho visou contribuir para o melhor entendimento da complexa história evolutiva dos crocodiliformes. Deste modo, são apresentados aqui, em duas partes distintas, os resultados obtidos durante o mestrado, que focou no estudo de dois Crocodyliformes fósseis. Na primeira parte, é descrita uma nova espécie de Baurusuchidae (Mesoeucrocodylia), baseada em um esqueleto completo coletado em General Salgado-SP (Formação Adamantina, Cretáceo Superior). Nomeado Aplestosuchus sordidus, o novo táxon foi incluído em uma análise filogenética no contexto dos Baurusuchidae, sendo posicionado em Baurusuchinae, como grupo-irmão com Baurusuchus albertoi. Além disso, na cavidade abdominal deste espécime, restos de outro indivíduo, associado a Sphagesauridae, foram preservados, revelando o primeiro registro inequívoco de conteúdos abdominais para Crocodyliformes fósseis. Assim, também é discutida a estrutura trófica do ambiente daquela época, amplamente dominada por crocodiliformes. Já a segunda parte envolveu a redescrição anatômica de Eocaiman cavernensis (Crocodylia, Caimaninae) do Eoceno Médio da Argentina. Esta importante espécie é presença constante em estudos filogenéticos sobre Caimaninae, sendo que a reavaliação de sua osteologia visou gerar novas informações anatômicas. Tais dados foram incorporados numa análise filogenética, no intuito de testar sua influência sobre a filogenia dos Caimaninae e demais Crocodylia. Adicionalmente, também foram desenvolvidas discussões acerca da paleobiogeografia e paleoecologia do gênero Eocaiman no contexto dos Caimaninae. / Crocodyliformes were much more diverse in the past than today. This incredible diversity is translated into a wide range of ecological niches occupied by these animals, many of which differ from the typical semiaquatic habit of the extant forms. In this context, the project developed during the MSc degree aimed to increase the knowledge about Crocodyliformes, with the study two fossil taxa, presented here in two separated parts. The first part includes the description of Aplestosuchus sordidus, a new species of Baurusuchidae (Mesoeucrocodylia), based on a nearly complete skeleton collected in deposits of the Adamantina Formation (Bauru Group, Late Cretaceous of Brazil). A phylogenetic analysis was performed to investigate the affinities of the new taxon, suggesting its sister-taxon relation to Baurusuchus albertoi, within Baurusuchinae. Additionally, the remains of a sphagesaurid crocodyliform were preserved in the abdominal cavity of the new baurusuchid, what would be the first time that a direct and unmistaken evidence of predation is recorded in fossil Crocodyliformes. This new finding confirms the important position that crocodyliforms had in the trophic structure of that environment. The second part of this work presents a re-evaluation of the anatomy of Eocaiman cavernensis (Crocodylia, Caimaninae) from the Middle Eocene of Argentina. This species, described by G. G. Simpson in 1933, is important due to its ubiquitous presence in phylogenetic studies of Caimaninae. Thus, its re-description aimed at revealing new anatomical information in order to clarify the relationships among taxa of this group. The new data was added to a previously published phylogenetic analysis and the results were discussed. In addition, the paleobiogeography and paleoecology of the genus Eocaiman was evaluated in the context of the Caimaninae.

Mesoeucrocodylia é um clado bem estabelecido, que circunscreve a maior parte da diversidade taxonômica e morfológica de Crocodyliformes. No entanto, questões amplas relacionadas à sua irradiação basal permanecem controversas. Trabalhos de cunho filogenético tem estabelecido hipóteses altamente contrastantes, em especial relacionadas à validade e inter-relações dos grupos Thalattosuchia, Sebecosuchia, Notosuchia, Peirosauridae e Trematochampsidae. Uma revisão filogenética ampla foi elaborada com o intuito de reavaliar a filogenia de Mesoeucrocodylia de maneira crítica. Para tal, baseou-se no estudo dos táxons envolvidos neste contexto, em especial os possivelmente atribuídos aos cinco subgrupos supracitados, mas também membros das outras principais linhagens de Mesoeucrocodylia, além de grupos externos imediatos ao clado. Os caracteres previamente propostos para este contexto também foram reavaliados, e novos caracteres propostos, visando abarcar a diversidade morfológica total dos diferentes táxons analisados. A matiz táxon-caráter resultante da revisão é composta por 122 táxons e 494 caracteres, que foi submetida à análise de parcimônia através do programa TNT (5000 RAS, TBR, Hold 20). O consenso estrito das 3575 árvores mais parcimoniosas resultantes (MPT) não concorda em sua totalidade com nenhuma hipótese prévia. A nova hipótese filogenética apresenta uma combinação de clados anteriormente propostos e relações pela primeira vez recuperadas. Thalattosuchia foi encontrado como o grupo de Mesoeucrocodylia mais basal, assim, grupo irmão de Metasuchia. Metasuchia, por sua vez, é formado por uma grande dicotomia com Neosuchia em um ramo e Gondwanasuchia no outro. Neosuchia é formado por Stomatosuchidae como ramo mais basal, seguido de Atoposauridae como o grupo irmão de uma politomia. Esta politomia envolve Tethysuchia, Goniopholididae, Bernissartia, e um clado congregando os Neosuchia derivados (Paralligatoridae, Susisuchus e Eusuchia). Gondwanasuchia circunscreve a maior diversidade dos táxons na presente análise sendo formado por uma politomia que envolve Doratodon, Peirosauridae + Trematochampsidae, Sebecidae + Mahajangasuchidae e Notosuchia. Assim, Sebecosuchia foi recuperado parafilético, com Baurusuchidae como um Notosuchia derivado. Adicionalmente, Sebecia, como originalmente proposto, não foi recuperado como uma hipótese mais parcimoniosa em todas as árvores, porém, encontra-se entre os possíveis arranjos dentre as MPT. / Mesoeucrocodylia is a well established clade encompassing the greatest taxonomic and morphological diversity within Crocodyliformes. However, its basal phylogeny remains poorly understood. Previous works highly disagree on the relationships and validity of an array of basal mesoeucrocodylian groups, particularly Thalattosuchia, Sebecosuchia, Notosuchia, Peirosauridae and Trematochampsidae. The Mesoeucrocodylia basal phylogeny was critically revaluated based on a broad revision. Taxa belonging to the aforementioned subgroups, as well as taxa assigned to other Mesoeucrocodylia major lineages and its immediate outgroups were reanalyzed. Characters previously proposed within this context were also revised and new characters added to cover the morphological diversity within the selected taxa. The final matrix is 122 taxa and 494 character and the parsimony analyses was performed in TNT (5000 RAS, TBR and Hold 20). The strict consensus of the 3575 most parsimonious trees (MPTs) does not fully agree to any of the previous phylogenies. The new analysis depicts a mix of known clades and relationships proposed for the first time. Thalattosuchia is the basal most Mesoeucrocodylia and sister group of Metasuchia. Metasuchia is formed by a dichotomy including Neosuchia on one branch and Gondwanasuchia on the other. Stomatosuchidae is the basal most Neosuchia, followed by Atoposauridae as the sister group of a polytomy encompassing Tethysuchia, Goniopholididae, Bernissartia and a clade of derived neosuchians (Paralligatoridae, Susisuchus and Eusuchians). Gondwanasuchia is formed by a basal polytomy including Doratodon, Peirosauridae + Trematochampsidae, Sebecidae + Mahajangasuchidae and Notosuchia. In this sense, Sebecosuchia was not depicted as a monophyletic group and Baurusuchidae was placed derived in the Notosuchia clade. In addition, Sebecia, as original, conceived was not recovered in all of the MPTs however it is a possible result among the MPTs.

Mesoeucrocodylia é um clado bem estabelecido, que circunscreve a maior parte da diversidade taxonômica e morfológica de Crocodyliformes. No entanto, questões amplas relacionadas à sua irradiação basal permanecem controversas. Trabalhos de cunho filogenético tem estabelecido hipóteses altamente contrastantes, em especial relacionadas à validade e inter-relações dos grupos Thalattosuchia, Sebecosuchia, Notosuchia, Peirosauridae e Trematochampsidae. Uma revisão filogenética ampla foi elaborada com o intuito de reavaliar a filogenia de Mesoeucrocodylia de maneira crítica. Para tal, baseou-se no estudo dos táxons envolvidos neste contexto, em especial os possivelmente atribuídos aos cinco subgrupos supracitados, mas também membros das outras principais linhagens de Mesoeucrocodylia, além de grupos externos imediatos ao clado. Os caracteres previamente propostos para este contexto também foram reavaliados, e novos caracteres propostos, visando abarcar a diversidade morfológica total dos diferentes táxons analisados. A matiz táxon-caráter resultante da revisão é composta por 122 táxons e 494 caracteres, que foi submetida à análise de parcimônia através do programa TNT (5000 RAS, TBR, Hold 20). O consenso estrito das 3575 árvores mais parcimoniosas resultantes (MPT) não concorda em sua totalidade com nenhuma hipótese prévia. A nova hipótese filogenética apresenta uma combinação de clados anteriormente propostos e relações pela primeira vez recuperadas. Thalattosuchia foi encontrado como o grupo de Mesoeucrocodylia mais basal, assim, grupo irmão de Metasuchia. Metasuchia, por sua vez, é formado por uma grande dicotomia com Neosuchia em um ramo e Gondwanasuchia no outro. Neosuchia é formado por Stomatosuchidae como ramo mais basal, seguido de Atoposauridae como o grupo irmão de uma politomia. Esta politomia envolve Tethysuchia, Goniopholididae, Bernissartia, e um clado congregando os Neosuchia derivados (Paralligatoridae, Susisuchus e Eusuchia). Gondwanasuchia circunscreve a maior diversidade dos táxons na presente análise sendo formado por uma politomia que envolve Doratodon, Peirosauridae + Trematochampsidae, Sebecidae + Mahajangasuchidae e Notosuchia. Assim, Sebecosuchia foi recuperado parafilético, com Baurusuchidae como um Notosuchia derivado. Adicionalmente, Sebecia, como originalmente proposto, não foi recuperado como uma hipótese mais parcimoniosa em todas as árvores, porém, encontra-se entre os possíveis arranjos dentre as MPT. / Mesoeucrocodylia is a well established clade encompassing the greatest taxonomic and morphological diversity within Crocodyliformes. However, its basal phylogeny remains poorly understood. Previous works highly disagree on the relationships and validity of an array of basal mesoeucrocodylian groups, particularly Thalattosuchia, Sebecosuchia, Notosuchia, Peirosauridae and Trematochampsidae. The Mesoeucrocodylia basal phylogeny was critically revaluated based on a broad revision. Taxa belonging to the aforementioned subgroups, as well as taxa assigned to other Mesoeucrocodylia major lineages and its immediate outgroups were reanalyzed. Characters previously proposed within this context were also revised and new characters added to cover the morphological diversity within the selected taxa. The final matrix is 122 taxa and 494 character and the parsimony analyses was performed in TNT (5000 RAS, TBR and Hold 20). The strict consensus of the 3575 most parsimonious trees (MPTs) does not fully agree to any of the previous phylogenies. The new analysis depicts a mix of known clades and relationships proposed for the first time. Thalattosuchia is the basal most Mesoeucrocodylia and sister group of Metasuchia. Metasuchia is formed by a dichotomy including Neosuchia on one branch and Gondwanasuchia on the other. Stomatosuchidae is the basal most Neosuchia, followed by Atoposauridae as the sister group of a polytomy encompassing Tethysuchia, Goniopholididae, Bernissartia and a clade of derived neosuchians (Paralligatoridae, Susisuchus and Eusuchians). Gondwanasuchia is formed by a basal polytomy including Doratodon, Peirosauridae + Trematochampsidae, Sebecidae + Mahajangasuchidae and Notosuchia. In this sense, Sebecosuchia was not depicted as a monophyletic group and Baurusuchidae was placed derived in the Notosuchia clade. In addition, Sebecia, as original, conceived was not recovered in all of the MPTs however it is a possible result among the MPTs.

Ovos fósseis de Crocodyliformes, Aves e Chelonii são artefatos reprodutivos incomuns, conhecidos a partir de registros em poucos países. Tornam-se ainda mais raros quando considerados apenas os achados oriundos de rochas mesozoicas. No Brasil, os registros são limitados à poucos ovos de Crocodyliformes do Cretáceo do Grupo Bauru, bem como um ovo de Chelonii de mesma idade. Desta forma, o presente estudo propôs-se a realizar a descrição de doze ovos fósseis coletados em Campina Verde-MG, e de outros dois provenientes de Álvares Machado e Pirapozinho, região de Presidente Prudente-SP, oriundos de rochas cretáceas (Grupo Bauru). Para tal, utilizou-se técnicas de análises ultraestruturais como Microscopia Eletrônica de Varredura, Espectrometria por Dispersão de Energia e Microscopia Óptica, além de Tomografia Computadorizada para verificar a ocorrência de embriões. Os resultados das análises sugerem a afinidade dos doze ovos de Campina Verde a Crocodyliformes e, pela topotipia do horizonte estratigráfico, a possível associação destes a Pissarrachampsa sera. Adicionalmente, o recorrente registro de ovos fósseis associados a restos esqueletais de crocodilianos notosúquios sugere um nível de cuidado parental presente no grupo. Já o espécime de Álvares Machado possui feições de Enantiornithes. Por fim, o ovo coletado em Pirapozinho possui características semelhantes às de ovos de quelônios Podocnemidae, o único grupo de Chelonii conhecido no afloramento de onde provém o ovo / Amniotes fossil eggs, such as Crocodyliformes, Aves and Chelonii, are known from few places worldwide, and the Mesozoic records are particularly rare. Similarly, the occurrence of eggs of these groups is also rare in Brazil and limited to few crocodylian eggs and a single Chelonii one from Cretaceous rocks. This work aimed to describe twelve fossil eggs collected in Campina Verde-MG, and two additional eggs from Álvares Machado and Pirapozinho, SP, all from Bauru Group rocks (Upper Cretaceous). The ultrastructural traits of the shells were analyzed by Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Optical Microscopy, in addition, Computadorized Tomography was applied to check the embryos occurrence. The twelve eggs from Campina Verde are associated to Crocodyliformes. In addition, the topotipic principle suggests an association of these eggs to the crocodyliform Pissarrachampsa sera. Additionally, the recurrent association of notosuchians fossil eggs and skeletal remains suggests a level of parental care in this group. The specimen from Álvares Machado is associated to Enantiornithes, and the egg from Pirapozinho shares traits with Podocnemidae eggs, which is the only known Chelonii group found in the outcrop where the egg came from

Com 23-24 espécies viventes, a diversidade atual de crocodilianos é irrisória quando comparada ao registro fóssil do grupo, principalmente se considerados todos os representantes de Crocodyliformes. À luz desta grande diversidade, este trabalho visou contribuir para o melhor entendimento da complexa história evolutiva dos crocodiliformes. Deste modo, são apresentados aqui, em duas partes distintas, os resultados obtidos durante o mestrado, que focou no estudo de dois Crocodyliformes fósseis. Na primeira parte, é descrita uma nova espécie de Baurusuchidae (Mesoeucrocodylia), baseada em um esqueleto completo coletado em General Salgado-SP (Formação Adamantina, Cretáceo Superior). Nomeado Aplestosuchus sordidus, o novo táxon foi incluído em uma análise filogenética no contexto dos Baurusuchidae, sendo posicionado em Baurusuchinae, como grupo-irmão com Baurusuchus albertoi. Além disso, na cavidade abdominal deste espécime, restos de outro indivíduo, associado a Sphagesauridae, foram preservados, revelando o primeiro registro inequívoco de conteúdos abdominais para Crocodyliformes fósseis. Assim, também é discutida a estrutura trófica do ambiente daquela época, amplamente dominada por crocodiliformes. Já a segunda parte envolveu a redescrição anatômica de Eocaiman cavernensis (Crocodylia, Caimaninae) do Eoceno Médio da Argentina. Esta importante espécie é presença constante em estudos filogenéticos sobre Caimaninae, sendo que a reavaliação de sua osteologia visou gerar novas informações anatômicas. Tais dados foram incorporados numa análise filogenética, no intuito de testar sua influência sobre a filogenia dos Caimaninae e demais Crocodylia. Adicionalmente, também foram desenvolvidas discussões acerca da paleobiogeografia e paleoecologia do gênero Eocaiman no contexto dos Caimaninae. / Crocodyliformes were much more diverse in the past than today. This incredible diversity is translated into a wide range of ecological niches occupied by these animals, many of which differ from the typical semiaquatic habit of the extant forms. In this context, the project developed during the MSc degree aimed to increase the knowledge about Crocodyliformes, with the study two fossil taxa, presented here in two separated parts. The first part includes the description of Aplestosuchus sordidus, a new species of Baurusuchidae (Mesoeucrocodylia), based on a nearly complete skeleton collected in deposits of the Adamantina Formation (Bauru Group, Late Cretaceous of Brazil). A phylogenetic analysis was performed to investigate the affinities of the new taxon, suggesting its sister-taxon relation to Baurusuchus albertoi, within Baurusuchinae. Additionally, the remains of a sphagesaurid crocodyliform were preserved in the abdominal cavity of the new baurusuchid, what would be the first time that a direct and unmistaken evidence of predation is recorded in fossil Crocodyliformes. This new finding confirms the important position that crocodyliforms had in the trophic structure of that environment. The second part of this work presents a re-evaluation of the anatomy of Eocaiman cavernensis (Crocodylia, Caimaninae) from the Middle Eocene of Argentina. This species, described by G. G. Simpson in 1933, is important due to its ubiquitous presence in phylogenetic studies of Caimaninae. Thus, its re-description aimed at revealing new anatomical information in order to clarify the relationships among taxa of this group. The new data was added to a previously published phylogenetic analysis and the results were discussed. In addition, the paleobiogeography and paleoecology of the genus Eocaiman was evaluated in the context of the Caimaninae.

Conceptualizations of actual biological patterns as preserved in the fossil record must accommodate the results of biotic and abiotic drivers of faunal dynamics. However, those conceptualizations also may reflect cognitive biases resulting from foundational philosophical stances. Whether fossils are conceptualized as the remains of biological entities or as geological objects will affect both taxonomic identifications and secondary inferences derived from those identifications. In addition, operational research bias centered on relativistic views of ‘importance’ of particular components (i.e., taxonomic or skeletal region) of the assemblage results in preferential documentation of some taxa and marginalization of others. I explored the consequences of those specific cognitive and operational biases through examination of Triassic and Eocene faunal assemblages in western North America. For the Triassic I focused on taxonomic and systematic treatments of Paleorhinus, a group of phytosaurs important for the establishment of biochronologic correlations. Specimen-level reexamination of Paleorhinus supported a restricted usage of Paleorhinus as a clade, dissolved a biochronologic connection between terrestrial and marine deposits, and indicated a prior compression of the early part of the Late Triassic as a result of previous conceptualizations of species. I reexamined the Otis Chalk tetrapod assemblage in light of new specimens and modern phylogenetic frameworks. My examination supported a restricted usage of the Otischalkian for biochronologic correlation of the Late Triassic, and emphasized the importance of apomorphic character-based specimen examinations in conjunction with detailed lithostratigraphy prior to the development of biochronologic schema. For the Eocene I focused on undocumented terrestrial reptiles from the late Uintan fauna of West Texas. Specifically I discovered new taxa and new geographic occurrences of amphisbaenians and caimanine crocodylians. The amphisbaenians represent the southernmost record of the clade in the North American Paleogene, and, when combined with other amphisbaenian records, document that the clade responded to late Paleogene climatic changes in ways different from the inferred mammalian response. The new taxon of caimanine crocodylian represents a new geographic and temporal record of that clade. That new record indicates that the biogeographic range of extant caimans represents a climate-driven restriction from a formerly more expansive range, and suggests that the previous geographic and temporal gap in paleodistribution data is related to sampling biases and is not a solely a biological phenomenon. These data indicate that reliable characterization of vertebrate faunal dynamics requires open acknowledgment and appropriate documentation of cognitive and operational biases that affect interpretations of paleontological data. / text