Development, function and evolution of the mammalian jaw joint and middle ear

本博士的目的是研究哺乳动物下颚和中耳的发育、功能和进化。哺乳动物在脊椎动物中是独一无二的，因为它们的下颚只有一块骨头，中耳有三块声音探测骨。化石记录记录了哺乳动物的祖先如何减少下颌“后牙”骨骼的大小和数量，这与独特的哺乳动物颌关节的形成有关，以及曾经形成祖先颌关节的骨骼如何被纳入中耳。在哺乳动物进化的某个阶段，动物的祖先和哺乳动物的下颌关节并排存在，具有双重觅食和听觉功能（Luo 2007, 2011; Tucker 2017）。最近的发育研究表明，虽然真动物的颌关节在胚胎中形成，但有袋动物和单孔动物出生时没有完全形成的哺乳动物颌关节。其中一个中耳小骨形成了一个临时的下颌铰链，单目幼鱼保留了一个双下颌关节，类似于与哺乳动物密切相关的化石（Anthwal et al. 2020）。这些发育数据与哺乳动物祖先的化石相结合，为了解哺乳动物颌和中耳的功能和进化提供了一个独特的数据集。该项目的目的是使用3D成像和计算生物力学来描述和比较发育中的和化石哺乳动物下颚的力学。学生将测试肌肉骨骼系统的重组和颌骨力学的变化是否是哺乳动物起源时颌骨和耳朵进化的关键（Lautenschlager etal . 2018）。这将通过通过独特的发育和化石数据集的成像创建3D数字模型，并使用有限元建模来绘制颌骨的受力图来实现。该学生还将使用保留耳朵和颌骨之间连接的突变小鼠模型，直接测试这些结构对颌骨功能的影响。该项目是一个新颖的，跨学科的进化发育生物学，古生物学和生物力学的组合。总的来说，管理团队在理解哺乳动物头骨的功能进化和哺乳动物颌骨和耳朵的发育生物学方面处于领先地位。因此，学生将获得广泛和有竞争力的技能，在实验室专门研究进化发育生物学和计算古生物学。

The aim of this PhD is to study the development, function and evolution of the mammalian jaw and middle ear. Mammals are unique among vertebrates in that they have a single bone in their lower jaw and possess three sounddetecting bones in their middle ear. The fossil record documents how the ancestors of mammals reduced the size and number of 'postdentary' bones in the jaw, linked to formation of a unique mammalian jaw joint, and how the bones that once formed the ancestral jaw joint were incorporated into the middle ear. At one point in mammalian evolution, animals existed with an ancestral and a mammalian jaw joint side-by-side, serving dual feeding and auditory functions (Luo 2007, 2011; Tucker 2017). Recent developmental studies reveal that while the eutherian jaw joint forms in the embryo, marsupials and monotremes are born without a fully formed mammalian jaw joint. One of the middle ear ossicles forms a temporary jaw hinge and monotreme juveniles retain a dual jaw joint, similar to that found in fossils closely related to mammals (Anthwal et al. 2020). This developmental data combined with fossils from the ancestors of mammals represent a unique dataset to understand the function and evolution of the mammalian jaw and middle ear. The aim of the project is to use 3D imaging and computational biomechanics to characterise and compare the mechanics of the developing and fossil mammalian jaw. The student will test if reorganisation of the musculoskeletal system and a change in the mechanics of the jaw was key to jaw and ear evolution at the origin of mammals (Lautenschlager et al. 2018). This will be achieved by creating 3D digital models via imaging of unique developmental and fossil datasets and using finite element modelling to map forces in the jaw. The student will also use mutant mouse models that retain the connection between the ear and jaw, to directly test the influence of these structures on jaw function. The project is a novel, interdisciplinary mix of evolutionary developmental biology, palaeontology and biomechanics. Collectively the supervisory team are leaders in understanding the functional evolution of the mammalian skull and the developmental biology of the mammalian jaw and ear. As such the student will gain a broad and competitive skill set, working in laboratories specialising in evolutionary developmental biology and computational palaeobiology.