Integrating the fossil record with computer simulation to reconstruct posture and locomotor evolution in the ancestors of mammals

现代哺乳动物的一个显著特征是它们如何站立和移动：它们将四肢直立在身体下方，这种“直立”的运动方式深刻地影响了它们的进化成功和生态多样性。化石记录显示，哺乳动物的早期祖先（大约3亿年前）的外貌和行动方式更像爬行动物，四肢伸展到身体的一侧。进化生物学中一个经久不衰的问题是，在哺乳动物的崛起过程中，从四肢伸展到直立的姿势是如何以及何时发生的。这个项目将利用与恐龙相媲美的哺乳动物祖先的特殊化石记录和现代物种的数据来回答这个基本问题。尖端的生物力学方法，最初是为航空航天和医学研究而开发的，将应用于开发复杂的计算机模拟灭绝物种的运动，几乎使它们复活，加深我们对典型哺乳动物特征的理解。这个项目的结果将为一个强有力的推广计划提供基础，该计划的目标是增加科学多样性，并消除对古生物学家的误解。在当地社区举办的夏季研讨会将使用物理和虚拟互动展示来鼓励那些来自代表性不足的群体的人将古生物学，生物力学和计算机模拟视为可访问的职业领域，从而激励下一代科学家。还将纳入当地高中生带薪暑期实习项目，为实习生提供研究、博物馆藏品管理和公共传播活动的第一手经验。学生们还将作为同伴的榜样，帮助在周边社区举办讲习班。研究成果将通过会议报告、开放获取出版物和在线网络研讨会向科学界传播，致力于展示古生物学和生物力学的跨学科研究。现代哺乳动物表现出显著的运动多样性，这是由于它们已灭绝的祖先——非哺乳动物的突触类动物在解剖学和功能上发生了深刻的转变。最根本的是姿势和步态的转变，从爬行动物的“伸展”到现存陆生哺乳动物的“直立”模式。尽管它在哺乳动物进化中至关重要，但人们对四肢伸展到直立的转变是如何以及何时发生的仍然知之甚少。此外，尚不清楚是什么解剖和机械因素促进或限制了这种转变。该项目将通过综合非哺乳动物突触类动物的典型化石记录，利用生物力学的前沿分析和模拟方法来解决这些问题，以揭示爬行动物向哺乳动物转变的历史。该项目将：1)在多个尺度上研究运动功能，从单个骨骼的结构转变到整个生物体的功能整合和表现；2)对肢体功能、表现和多功能性进行严格和定量的评估；3)对一系列灭绝物种的三维步态周期进行动态模拟；4)重现现代哺乳动物运动的一系列事件和适应性驱动因素。通过利用特殊的化石材料，现代物种的详细解剖数据和复杂的计算生物力学方法，该项目将产生第一个大规模的，基于物理的姿势和运动性能的评估，在许多关键分类群跨越蔓延到直立的过渡。所使用的方法和获得的见解将为解剖学和力学因素如何在谱系中塑造宏观进化变化并产生新的主要动物分支提供强有力的新视角，为脊椎动物历史上其他主要进化转变的严格调查铺平道路。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 distinguishing feature of modern mammals is how they stand and move: they hold their limbs straight underneath their body, and this ‘erect’ mode of locomotion has profoundly influenced their evolutionary success and ecological diversity. The fossil record shows that the early ancestors of mammals (~300 million years ago) looked and moved more like reptiles, using a ‘sprawled’ posture with the limbs held out to the side of the body. An enduring question in evolutionary biology is how and when the transition from sprawled to erect posture occurred during the rise of mammals. This project will use the exceptional fossil record of mammal ancestors – rivalling that of dinosaurs – and data from modern species to answer this fundamental question. Cutting-edge biomechanical methods, originally developed for aerospace and medical research, will be applied to develop sophisticated computer simulations of locomotion in extinct species, virtually bringing them back to life and deepening our understanding of a quintessentially mammalian characteristic. The results of this project will provide the foundation for a strong program of outreach that targets increasing diversity in the sciences, and combats misperceptions about paleontologists. Summer workshops, hosted in local communities, will use both physical and virtual interactive displays to encourage those from underrepresented groups to see paleontology, biomechanics, and computer simulation as accessible career fields, stimulating the next generation of scientists. Paid summer internship programs involving local high school students will also be incorporated, providing interns first-hand experience in research, museum collections management and public communication activities. Students will also act as near-peer role models in helping to deliver workshops in surrounding communities. Research outcomes will be disseminated to the scientific community through conference presentations, open-access publications, and online webinars dedicated to showcasing interdisciplinary research in paleontology and biomechanics.Modern mammals display remarkable locomotor diversity, which has been facilitated by profound transformation in anatomy and function that occurred in their extinct ancestors, the non-mammalian synapsids. Fundamental to this was a shift in stance and gait, from a reptilian ‘sprawl’ to the ‘erect’ mode used by living terrestrial mammals. Despite its pivotal importance in mammal evolution, how and when the sprawling-to-erect transition occurred remains poorly understood. Furthermore, it is unclear what anatomical and mechanical factors facilitated or constrained this transition. This project will address these issues by synthesizing the exemplary fossil record of non-mammalian synapsids with cutting-edge analytical and simulation approaches in biomechanics to unravel the history of locomotor transformation on the line to mammals. The project will: 1) tackle locomotor function at multiple scales, from structural transformation in individual bones through to whole-organism functional integration and performance; 2) produce rigorous and quantitative assessments of limb function, performance, and versatility; 3) develop dynamic simulations of three-dimensional gait cycles in a range of extinct species; and 4) recreate the sequence of events and adaptive drivers that culminated in modern mammalian locomotion. By leveraging exceptional fossil material, detailed anatomical data from modern species and sophisticated computational biomechanical methods, the project will produce the first broad-scale, physics-based assessments of posture and locomotor performance in numerous key taxa spanning the sprawling-to-erect transition. The methods used and insights gained will provide a powerful, new perspective on how anatomical and mechanical factors can shape macroevolutionary change in a lineage and give rise to new major clades of animals, paving the way forward for rigorous investigation of other major evolutionary transitions in vertebrate history.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.