美国哈佛大学Stephanie E. Pierce、Blake V. Dickson研究组的最新研究揭示，功能性适应性景观预测了四肢动物起源时的陆地能力。这一研究成果在线发表于2020年11月25日的《自然》。

在本研究中，研究人员分析了从鳍到四肢过渡过程中40个绝种四足动物的三维保存肱骨，并使用功能上有根据的生态适应景观重建了陆地运动的演变。研究表明，肱骨形状的进化变化是由生态和系统发育驱动的，并且与运动有关功能的折衷相关。针对水生鱼类和陆地皇冠四足动物恢复了两种不同的适应性景观，每种景观都由功能特异的不同组合定义。肱骨四足动物具有一套独特的功能适应性，但不符合它们自己的预测适应峰。

取而代之的是，肱骨四足动物位于陆地皇冠四足动物进化的底部，表明陆地运动能力随四肢的起源而发生。该研究结果表明，肱骨四足动物在陆地探索的初始阶段可能已经使用了过渡步态，这些步态由于其两栖习性的相对选择性压力而稳定。直到皇冠四足动物失去了其祖先“L形”肱骨，才出现了有效的基于肢体的运动，这为陆地四足动物的多样化和建立现代生态位奠定了基础。

据了解，在四足动物进化过程中，以肢体为基础陆地运动能力的获取一直是一个有争论的问题。目前对从水生到陆地运动过渡的理解主要基于一些典型的化石，例如提塔利克鱼、棘螈、鱼石螈和彼得普斯螈。但是，孤立的骨元素可能会揭示隐藏的功能多样性，从而提供更全面的进化观点。

附：英文原文

Title: Functional adaptive landscapes predict terrestrial capacity at the origin of limbs

Author: Blake V. Dickson, Jennifer A. Clack, Timothy R. Smithson, Stephanie E. Pierce

Issue&Volume: 2020-11-25

Abstract: The acquisition of terrestrial, limb-based locomotion during tetrapod evolution has remained a subject of debate for more than a century1,2. Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik3, Acanthostega4, Ichthyostega5 and Pederpes6. However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective7. Here we analyse 40 three-dimensionally preserved humeri from extinct tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes8,9,10 to reconstruct the evolution of terrestrial locomotion. We show that evolutionary changes in the shape of the humerus are driven by ecology and phylogeny and are associated with functional trade-offs related to locomotor performance. Two divergent adaptive landscapes are recovered for aquatic fishes and terrestrial crown tetrapods, each of which is defined by a different combination of functional specializations. Humeri of stem tetrapods share a unique suite of functional adaptations, but do not conform to their own predicted adaptive peak. Instead, humeri of stem tetrapods fall at the base of the crown tetrapod landscape, indicating that the capacity for terrestrial locomotion occurred with the origin of limbs. Our results suggest that stem tetrapods may have used transitional gaits5,11 during the initial stages of land exploration, stabilized by the opposing selective pressures of their amphibious habits. Effective limb-based locomotion did not arise until loss of the ancestral ‘L-shaped’ humerus in the crown group, setting the stage for the diversification of terrestrial tetrapods and the establishment of modern ecological niches12,13.

DOI: 10.1038/s41586-020-2974-5

Source: https://www.nature.com/articles/s41586-020-2974-5