The morpho-functional evolution of bird beaks and skulls

人们广泛地描述了某些鸟的喙和头骨是如何被改造和适应以不同的食物为食的。达尔文的雀类是一个如此经典的例子，以至于在这种情况下引用它们几乎是陈词滥调，但它们相当有效地说明了该领域目前的研究水平。尽管几十年来对生态学和最近的发育进行了详细的研究，但直到今年早些时候，一项研究才最终开始量化不同形状的雀类头骨和喙是如何产生不同的咬合力和抗骨折能力的——这些特征决定了这些鸟类能够利用的食物和环境。这可能是一个很好的例子，与在这个领域进行的定量分析相比，我们认为我们对鸟类及其头骨的形态、功能和多样性了解多少。除了将不同的形状与不同的环境联系起来之外，我们对鸟喙和头骨的形状如何影响它们的功能和喂养生态知之甚少。尽管颅骨和喙的形态对鸟类的多样性有很大的贡献。例如，所有以腐肉或大种子为食的鸟类，是否都有相同形状和功能的头骨和喙？它们是否以相似的方式弯曲和受力，并产生等量的咬合力？为了以同样的方式发挥作用，它们真的需要有同样的大小和形状吗？此外，由于鸟类的大多数成员都能飞，因此鸟类通常被认为是典型的动物，由于需要减轻体重（质量），它们可以采用的不同身体形式的数量受到限制。事实果真如此吗？有没有未实现的头骨和喙的形状可以做得更好？为什么我们在现存的动物身上看不到这种形状的喙和头骨呢？这项研究着手解决这些问题，以及这对鸟类的肌肉骨骼进化和多样性意味着什么。我们的团队拥有专业知识，可以采用一系列方法来量化头骨形状和生物力学功能的变化，并将其与我们开创的新工具联系起来，以询问假设或祖先形态的功能。在我们之间，我们有相关动物的技术能力、经验和知识，可以定量确定积极处理食物的特定鸟类群体的头骨和喙形变化模式。然后，我们将利用我们在头骨生物力学和工程分析方面的强大背景来确定摄食生物力学的功能变化，以及具有相似摄食生态的鸟类是否具有相似的喙和头骨形状，并以相同的方式发挥作用。如果在形式和功能之间有紧密的联系，并且趋同或平行进化在起作用，我们就会预测这种情况。我们还将测试共同的祖先在决定我们所看到的不同形状和功能范围方面所起的作用。使用我们最近开发的软件工具，我们将发现假设的或祖先的头骨和喙的形状是否比我们现有的鸟类群体拥有的更能抵抗进食负荷。最后，我们将确定鸟喙形状的变化在多大程度上取决于脑壳形状的变化，以及鸟喙和脑壳形状之间的松散关系是否有助于鸟类发展出更多样化的头骨形态。来自不同学科的研究人员将从这项工作中受益——比较解剖学家、生物力学家、进化和发育生物学家、古生物学家和生物医学工程师。通过对年轻科学家的多学科培训和与欧盟的海外合作，英国的科学基础将受益。这项工作的视觉方面，以及对鸟类的关注，可能会吸引公众，提供公众参与的机会和媒体的兴趣。

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.