Esta tesis estudia los cambios mofológicos ocurridos en el cráneo durante la evolución de los hom... more Esta tesis estudia los cambios mofológicos ocurridos en el cráneo durante la evolución de los hominoideos. Se analiza el crecimiento en la ontogenia mediante el estudio del mecanismo de crecimiento del hueso, que se basa en las actividades celulares responsables de la ...
life-history and evolution of fossil vertebrates may be studied through the analysis of their min... more life-history and evolution of fossil vertebrates may be studied through the analysis of their mineralised tissues. The mineralization of bone tissue during life allows the preservation of skeletal parts after the death of the organism, which become –together with teeth– the bulk of the mammalian fossil record. Although traditionally considered a static element, bone is in fact a dynamic and complex tissue that grows throughout life of the organism, changing in size, shape and position (Enlow, 1982) in response to a variety of internal and external stimuli. The dynamic nature of bone tissue together with the strength allow bones to perform structural functions –providing mobility, support, and protection for the body, as well as a reservoir for essential minerals. At the histological level, bones grow and react to stimuli modulating the activity of the cells responsible for the formation and removal of bone tissue. As a consequence, histological features due to the activity of the bo...
Age and sex selection of prey is an aspect of predator ecology which has been extensively studied... more Age and sex selection of prey is an aspect of predator ecology which has been extensively studied in both temperate and African ecosystems. This dimension, along with fecundity, survival rates of prey and mortality factors other than predation are important in laying down the population dynamics of prey and have important implications in the management of species. A carnivore den located in the short-grassland ecological unit of the Serengeti was studied. Sex- and age- class (using five age categories) of the wildebeest remains recovered were analyzed through horn morphology, biometrics of the bones and tooth wear patterns. We compared our results with previous studies from lion and hyaena kills through multivariate analyses. Seasonality of the accumulation was analyzed through tooth histology. PCA and CVA results show that age class selection by predators depends on season, habitat-type, and growth rate of the wildebeest population. Female-biased predation was found to contradict classical hypotheses based on territorial male behaviour. The lion and spotted hyaena showed strong selection on age classes, contrary to previous studies. Migratory wildebeest sex ratio is regulated through differential predation by seasons and female deaths in the wet season are a trade-off for population stability. These data are crucial for an effective management of the species and the new method created may be useful for different carnivore species and their prey.
ABSTRACT The clade Archosauria contains two very different sister groups in terms of diversity (n... more ABSTRACT The clade Archosauria contains two very different sister groups in terms of diversity (number of species) and disparity (phenotypic variation): Crurotarsi (taxa more closely related to crocodiles than to birds) and Ornithodira (pterosaurs and dinosaurs including birds). The extant species of Crurotarsi may constitute a biased sample of past biodiversity regarding growth patterns and metabolic rates. Bone histological characters can be conserved over hundreds of millions of years in the fossil record and potentially contain information about individual age at death, age at sexual maturity, bone growth rates, and basal metabolic rates of extinct vertebrates. Using a sample of extant amniotes, we have constructed a paleobiological model to estimate bone growth rate from bone histological traits. Cross-validation tests show that this model is reliable. We then used it to estimate bone growth rates in a sample of extinct archosaurs including Crurotarsi and Ornithodira. After testing for phylogenetic signal, optimization of femoral growth rates through squared change parsimony onto a time-calibrated tree of amniotes shows two divergent evolutionary trends: whereas bone growth rates increase from the last common ancestor of Ornithodira to extant birds, they decrease from the last common ancestor of Crurotarsi to extant crocodiles. However, we conclude, on the basis of recent evidence for unidirectional airflow in the lungs of alligators, that crocodiles may have retained the capacity of growing at high rates.
Esta tesis estudia los cambios mofológicos ocurridos en el cráneo durante la evolución de los hom... more Esta tesis estudia los cambios mofológicos ocurridos en el cráneo durante la evolución de los hominoideos. Se analiza el crecimiento en la ontogenia mediante el estudio del mecanismo de crecimiento del hueso, que se basa en las actividades celulares responsables de la ...
life-history and evolution of fossil vertebrates may be studied through the analysis of their min... more life-history and evolution of fossil vertebrates may be studied through the analysis of their mineralised tissues. The mineralization of bone tissue during life allows the preservation of skeletal parts after the death of the organism, which become –together with teeth– the bulk of the mammalian fossil record. Although traditionally considered a static element, bone is in fact a dynamic and complex tissue that grows throughout life of the organism, changing in size, shape and position (Enlow, 1982) in response to a variety of internal and external stimuli. The dynamic nature of bone tissue together with the strength allow bones to perform structural functions –providing mobility, support, and protection for the body, as well as a reservoir for essential minerals. At the histological level, bones grow and react to stimuli modulating the activity of the cells responsible for the formation and removal of bone tissue. As a consequence, histological features due to the activity of the bo...
Age and sex selection of prey is an aspect of predator ecology which has been extensively studied... more Age and sex selection of prey is an aspect of predator ecology which has been extensively studied in both temperate and African ecosystems. This dimension, along with fecundity, survival rates of prey and mortality factors other than predation are important in laying down the population dynamics of prey and have important implications in the management of species. A carnivore den located in the short-grassland ecological unit of the Serengeti was studied. Sex- and age- class (using five age categories) of the wildebeest remains recovered were analyzed through horn morphology, biometrics of the bones and tooth wear patterns. We compared our results with previous studies from lion and hyaena kills through multivariate analyses. Seasonality of the accumulation was analyzed through tooth histology. PCA and CVA results show that age class selection by predators depends on season, habitat-type, and growth rate of the wildebeest population. Female-biased predation was found to contradict classical hypotheses based on territorial male behaviour. The lion and spotted hyaena showed strong selection on age classes, contrary to previous studies. Migratory wildebeest sex ratio is regulated through differential predation by seasons and female deaths in the wet season are a trade-off for population stability. These data are crucial for an effective management of the species and the new method created may be useful for different carnivore species and their prey.
ABSTRACT The clade Archosauria contains two very different sister groups in terms of diversity (n... more ABSTRACT The clade Archosauria contains two very different sister groups in terms of diversity (number of species) and disparity (phenotypic variation): Crurotarsi (taxa more closely related to crocodiles than to birds) and Ornithodira (pterosaurs and dinosaurs including birds). The extant species of Crurotarsi may constitute a biased sample of past biodiversity regarding growth patterns and metabolic rates. Bone histological characters can be conserved over hundreds of millions of years in the fossil record and potentially contain information about individual age at death, age at sexual maturity, bone growth rates, and basal metabolic rates of extinct vertebrates. Using a sample of extant amniotes, we have constructed a paleobiological model to estimate bone growth rate from bone histological traits. Cross-validation tests show that this model is reliable. We then used it to estimate bone growth rates in a sample of extinct archosaurs including Crurotarsi and Ornithodira. After testing for phylogenetic signal, optimization of femoral growth rates through squared change parsimony onto a time-calibrated tree of amniotes shows two divergent evolutionary trends: whereas bone growth rates increase from the last common ancestor of Ornithodira to extant birds, they decrease from the last common ancestor of Crurotarsi to extant crocodiles. However, we conclude, on the basis of recent evidence for unidirectional airflow in the lungs of alligators, that crocodiles may have retained the capacity of growing at high rates.
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