The morpho-functional evolution of bird beaks and skulls

点击翻译按钮获取中文摘要

It is widely described how certain bird beaks and skulls are modified and adapted for feeding on distinct and different foodstuffs. Darwin's finches are such a classic example that to cite them in this context is almost a cliché, yet they illustrate the current level of research in this area quite effectively. Despite decades of detailed ecological and more recently developmental studies, it was only earlier this year that a study finally began to quantify how different shaped finch skulls and beaks generated different bite forces and resistance to fracture - features which dictate which foodstuffs and environments these birds are capable of exploiting. This is probably a good example of how much we think we know about form, function and diversity of birds and their skulls, compared to how much quantitative analysis has actually been performed in this area. We do not know a huge deal about how the shapes of bird beaks and skulls influence their function and feeding ecology, beyond just linking different shapes to different environments. This is despite the fact that cranial and beak morphology contributes to a significant amount of avian diversity. For example, do all birds that feed on carrion, or large seeds, have skulls and beaks that are shaped the same, and function in the same way? Do they bend and stress in a similar manner, and generate equivalent amounts of bite force? And to function in the same manner, do they indeed need to be the same size and shape? Furthermore, because most members of the group can fly, birds are often assumed to be a classic example of animals that are constrained in the number of different body forms they can adopt by the need to reduce weight (mass). Is this indeed the case? Are there unrealised shapes of skulls and beaks that could do the job better? And why do we not see beaks and skulls shaped in this manner in living animals? This study sets out to address these questions, and what this means for musculoskeletal evolution and diversity in birds. Our team has the expertise to employ a range of methodologies to quantify variation in form and biomechanical function in skulls, and link this to new tools that we have pioneered to interrogate the function of hypothetical or ancestral morphologies. Between us we have the technical ability, experience and knowledge of the animals concerned to quantitatively determine the patterns of skull and beak shape variation in selected groups of birds that actively process their food. We will then use our strong background in biomechanical and engineering analysis of skulls to determine functional variation in feeding biomechanics, and whether birds that share similar feeding ecologies are have similar shaped beaks and skulls, and function in the same manner. We would predict this to be the case if there were a tight link between form and function and convergent or parallel evolution were at play. We will also test what role shared ancestry plays in determining the range of different shapes and functions we see. Using our recently developed software tools we will find out if hypothetical or ancestral skull and beak shapes were better at resisting feeding loads than those possessed by our living bird groups. Finally, we will determine to what extent changes in the shape of the beak are contingent on changes to the shape of the braincase, and whether a loose relationship between beak and braincase shape can help birds develop more diverse skull morphologies. Researchers from a variety of disciplines will benefit from this work - comparative anatomists, biomechanists, evolutionary and developmental biologists, palaeontologists, and biomedical engineers. There will be benefits to the UK science base through multidiscplinary training of young scientists and overseas EU collaboration. The visual aspect of this work, and the focus on birds, is likely to appeal to the general public, offering public engagement opportunities and media interest.