Neurological adaptations for flight - correlating form and function in the avian cerebellar flocculus

现存的鸟类是从不会飞的祖先进化而来的。最终使飞行成为可能的变化不仅包括修改兽脚亚目恐龙的身体结构和进化羽毛，还需要大脑和感官的发展来应对地面以外的生活。为了飞行，鸟需要从平衡器官和视觉信息中获得关于其在空中位置的详细反馈。这些信号的处理主要发生在大脑中一个叫做小叶的区域，在鸟的大脑中很容易看到，因为它像手指一样从小脑两侧伸出来。小叶在不同种类之间的大小差异很大，由于其平衡功能，这种大小的变化可能与某些类型的飞行行为有关。这种变化也可能与物种生活的栖息地有关，因为在森林等封闭环境中飞行需要不同的飞行技能。现代的x射线微型ct技术现在使我们能够看到活鸟和化石鸟的头骨内部，揭示现代鸟类的大脑是如何进化的。利用CT分析，小叶的大小可以在恐龙、现存和灭绝的鸟类中确定，因为它的形状——以及整个大脑的形状——被印在头骨的内表面上。小叶大小与飞行能力有关的可能性使一些古生物学家从这种结构推断出始祖鸟等早期鸟类的飞行能力。然而，小叶大小和飞行行为之间的关系从未被测试过。这可能是因为放置小叶的骨袋的尺寸高估了它的大小，因为在小叶和骨头之间还有其他组织。也可能是小叶的大小与鸟的整体大小有关，而不是与它的飞行能力或栖息地偏好有关。这个项目打算通过CT扫描近100个生物物种的头骨来测试这些可能性，并从生活中容纳大脑的内部空间创建“虚拟大脑模型”。每个“虚拟大脑”中小叶的体积将被测量和统计分析，以确定小叶的大小是否可以用来预测飞行行为和/或栖息地，或者鸟类的大小是否是控制因素。如果没有发现紧密的联系，我们就会知道古生物学家应该避免根据小叶的大小来推测灭绝物种的飞行能力。或者，如果发现了它们之间的关系，我们的测试将为古生物学家提供一个工具，来检验目前关于鸟类飞行进化的观点，以及从恐龙到鸟类的过渡。

Living birds evolved from a flightless ancestor. The changes that eventually made flight possible not only involved modifying the theropod dinosaur body plan and evolving feathers, but also required the brain and senses to be developed to cope with life off the ground. To fly, a bird needs detailed feedback about its position in the air from its organs of balance, and also from visual information. The processing of these signals mostly occurs in a region of the brain called the flocculus, which is easy to see on a bird brain because it projects like a finger from the sides of the cerebellum. The flocculus varies greatly in size between species and, because of its function in balance, this size variation may relate to certain kinds of flying behaviour. The variation might also relate to the habitat in which a species lives, because flying in enclosed environments such as forests requires different flying skills to flying over open ground. Modern X-ray micro-CT techniques now allow us to see inside the skull of both living and fossil birds, revealing how the brain of modern birds has evolved. Using CT analysis, the size of the flocculus can be determined in dinosaurs and living and extinct birds, because its shape - and that of the brain as a whole - is impressed on the inner surface of the skull. The likelihood that flocculus size relates to flying ability has led some palaeontologists to infer flying ability for early birds such as Archaeopteryx from this structure. However, the relationship between flocculus size and flying behaviour has never been tested. It might be that the dimensions of the bony pocket that houses the flocculus are an overestimate of its size because other tissues lie between the flocculus and the bone. It might also be that the size of the flocculus is related to the overall size of the bird rather than to its flying ability or habitat preference. This project intends to test these possibilities by CT scanning the skulls of nearly 100 living species, and creating 'virtual brain models' from the internal space that housed the brain in life. The volume of the flocculus in each 'virtual brain' will be measured and analysed statistically to find out if flocculus size can be used to predict flying behaviour and/or habitat, or whether the size of the bird is the controlling factor. If strong relationships are not found we will know that palaeontologists should avoid speculating on the flying ability of extinct species based on flocculus size. Alternatively, if relationships are found, our test will have provided palaeontologists with a tool to test current ideas about the evolution of avian flight, and the transition from dinosaurs to birds.