Collaborative Research: Evolving the mammalian forelimb: modeling musculoskeletal transformation in the forerunners of mammals

哺乳动物的一个独特特征是它们的前肢形状和功能各不相同，包括用于奔跑、攀爬、挖掘、游泳和飞行的高度不同的前肢。没有其他动物群体有如此多样的前肢，哺乳动物前肢的灵活性似乎是该群体成功的关键原因。在化石记录中发现的第一个哺乳动物近亲有3亿多年的历史，与现存的哺乳动物形成了鲜明的对比：它们的前肢显示出非常有限的形状和功能范围。哺乳动物灵活的前肢是如何从这些看似受限的祖先进化而来的？前肢的变化是否增加了哺乳动物探索新生活方式的能力？该研究项目将使用最先进的技术，以及来自化石和现代动物的大量数据，重建古代哺乳动物近亲的前肢结构和功能，并测试前肢的变化是否与它们的生态多样性增加有关。研究结果将加深我们对哺乳动物一个典型特征的进化过程的理解，以及它在蝙蝠、鼹鼠、鲸鱼、马和人类等动物的进化过程中所起的作用。这项研究将通过屡获殊荣的YouTube频道“the Brain Scoop”制作的一系列教育在线视频进行传播。该系列将包括三集描述研究的不同阶段，两集描述结果及其意义。观众对视频的反应将被用来评估在线视频作为科学教育工具的有效性。现代哺乳动物表现出显著的生态形态多样性，其基础是前肢的进化以提供新的功能（如飞行、跑步、游泳和挖掘）。相比之下，哺乳动物的祖先——非哺乳动物的下孔纲——是广义的陆生四足动物，生态范围似乎有限。哺乳动物风格的前肢，包括一个完全可移动的肩胛骨，面向腹的球窝肩关节，以及“直立”的肢体姿势和运动，是祖先突触肌肉骨骼系统深刻重组的结果。从大量的突触类化石记录中，该项目整合了多种方法技术，以确定前肢的形态功能转化如何影响突触类进化的速度和模式。严格的形态计量学分析将量化前肢骨骼元素的形状差异，并确定形态学的主要变化。尖端的生物力学分析将形态变化与功能转换联系起来。而且，先进的系统发育建模技术将确定形态和功能的变化是否会导致多样化率的增加。主要产品包括一个新的综合元树，一个广泛的几何形态测量数据集，以及在突触进化的系统发育信息阶段的10个分类群的3D肌肉骨骼模型。结合起来，该项目将建立一个强大的比较框架，以量化已灭绝动物的肌肉骨骼转化，并为具有重要适应价值的集成解剖学模块提供独特的进化视角。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A unique feature of mammals is their many different forelimb shapes and functions, including highly distinct forelimbs for running, climbing, digging, swimming, and flying. No other group of animals has such diverse forelimbs, and the flexibility of mammal forelimbs seems to be a key reason for the group's success. The first mammal relatives found in the fossil record are over 300 million years old, and are a striking contrast to living mammals: their forelimbs show a very limited range of shapes and functions. How did the evolutionarily-flexible forelimbs of mammals evolve from such seemingly constrained ancestors, and did changes to the forelimb increase the ability of mammals to explore new ways of life? This research project will use state-of-the-art techniques, and extensive data from fossils and modern animals, to reconstruct forelimb structure and function in ancient mammal relatives, and to test whether changes to the forelimb correlate with increases in their ecological diversity. The results will deepen our understanding of the evolution of a quintessential characteristic of mammals, and its role in the evolution of animals as distinct as bats, moles, whales, horses, and humans. Dissemination of the research will occur through a series of educational online videos produced by the award-winning YouTube Channel "The Brain Scoop". The series will include three episodes describing different stages of the research, and two episodes that describe the results and their significance. Audience responses to the videos will be used to evaluate the effectiveness of online videos as a tool for science education.Modern mammals display remarkable ecomorphological diversity, which is underpinned by exaptation of the forelimb to serve novel functions (e.g. flying, running, swimming, and digging). In contrast, the ancestors of mammals - the non-mammalian synapsids - are generalized terrestrial tetrapods with seemingly limited ecological scope. The mammalian-style forelimb, including a fully mobile scapula, ventrally oriented ball-and-socket shoulder joint, and "upright" limb posture and movement, is the result of a profound reorganization of the ancestral synapsid musculoskeletal system. Drawing from the extensive synapsid fossil record, this project integrates a diverse set of methodological techniques to pinpoint how morphofunctional transformation of the forelimb influenced the tempo and mode of phenotypic evolution of the synapsid clade. Rigorous morphometric analyses will quantify shape disparity in forelimb skeletal elements and identify major shifts in morphology. Cutting-edge biomechanical analyses will correlate morphological shifts with functional transformation. And, advanced phylogenetic modeling techniques will determine whether shifts in morphology and function resulted in increases in diversification rates. Key products include a new comprehensive metatree of Synapsida, an extensive geometric morphometric dataset, and 3D musculoskeletal models of ten taxa at phylogenetically informative stages of synapsid evolution. Combined, this project will build a robust comparative framework to quantify musculoskeletal transformations in extinct animals and provide a unique evolutionary perspective on an integrated anatomical module of significant adaptive value.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.