Fish Frank E
Department of Biology, West Chester University, 750 S. Church St., West Chester, PA 19383, USA
Integr Comp Biol. 2016 Dec;56(6):1285-1297. doi: 10.1093/icb/icw123. Epub 2016 Oct 3.
Re-invasion of the aquatic environment by terrestrial vertebrates resulted in the evolution of species expressing a suite of adaptations for high-performance swimming. Examination of swimming by secondarily aquatic vertebrates provides opportunities to understand potential selection pressures and mechanical constraints, which may have directed the evolution of these aquatic species. Mammals and birds realigned the body and limbs for cursorial movements and flight, respectively, from the primitive tetrapod configuration. This realignment produced multiple solutions for aquatic specializations and swimming modes. Initially, in the evolution of aquatic mammals and birds, swimming was accomplished by using paired appendages in a low-efficiency, drag-based paddling mode. This mode of swimming arose from the modification of neuromotor patterns associated with gaits characteristic of terrestrial and aerial locomotion. The evolution of advanced swimming modes occurred in concert with changes in buoyancy control for submerged swimming, and a need for increased aquatic performance. Aquatic mammals evolved three specialized lift-based modes of swimming that included caudal oscillation, pectoral oscillation, and pelvic oscillation. Based on modern analogs, a biomechanical model was developed to explain the evolution of specialized aquatic mammals and their transitional forms. Subsequently, fossil aquatic mammals were described that validated much of the model. However, for birds, which were adapted for aerial flight, fossil evidence has been less forthcoming to explain the transition to aquatic capabilities. A biomechanical model is proposed for birds to describe the evolution of specialized lift-based foot and wing swimming. For both birds and mammals, convergence in morphology and propulsive mechanics is dictated by the need to increase speed, reduce drag, improve thrust output, enhance efficiency, and control maneuverability in the aquatic environment.
陆生脊椎动物重新侵入水生环境导致了一系列适应高效游泳的物种的进化。对次生水生脊椎动物游泳的研究为理解可能指导这些水生物种进化的潜在选择压力和机械限制提供了机会。哺乳动物和鸟类分别从原始四足动物的形态重新调整身体和四肢以适应 cursorial 运动和飞行。这种重新调整为水生特化和游泳模式产生了多种解决方案。最初，在水生哺乳动物和鸟类的进化过程中，游泳是通过以低效的、基于阻力的划水模式使用成对的附肢来完成的。这种游泳模式源于与陆地和空中运动特征步态相关的神经运动模式的改变。先进游泳模式的进化与水下游泳浮力控制的变化以及对提高水生性能的需求同时发生。水生哺乳动物进化出了三种基于升力的特殊游泳模式，包括尾鳍摆动、胸鳍摆动和腹鳍摆动。基于现代类似物，开发了一个生物力学模型来解释特殊水生哺乳动物及其过渡形式的进化。随后，描述了化石水生哺乳动物，验证了该模型的大部分内容。然而，对于适应空中飞行的鸟类来说，解释向水生能力过渡的化石证据却较少。本文提出了一个鸟类的生物力学模型来描述基于升力的特殊足部和翅膀游泳的进化。对于鸟类和哺乳动物来说，形态和推进力学的趋同是由在水生环境中提高速度、减少阻力、提高推力输出、增强效率和控制机动性的需求所决定的。
