能行走的肺鱼鳍
鱼儿会游泳，鸟儿会飞翔，歌里都是这么唱的，然而一项新的研究揭示，至少一种古老的鱼类能够在地面上散步。
非洲肺鱼（Protopterus annectens）是一种具有2.3亿年历史的物种，被发现于一些非洲国家（例如塞内加尔）的回水区。一直有传闻说这种鱼类能够沿着河床大步行走。
如今，研究人员用录像机捕捉了这种生物在实验室储水池中的活动场景，发现肺鱼不但能够行走，而且还能够利用生长在吻和尾之间的腹部上的瘦鳍跳跃。
当肺鱼在水池的地面上缓慢地行走时，它们会将身体抬离地面——通常只有四足的陆生动物才会这样做。
芝加哥大学的古生物学家Heather M. King和同事日前在美国《国家科学院院刊》网络版上报告了这一研究成果。
研究小组推测，与游水相比，行走可能不太容易吸引捕食者，或是吓走猎物。
肺鱼是陆生动物祖先的近亲，因此研究人员认为，这项工作表明，沿着地表散步的能力可能在生物从海洋迁移到旱地之前便已经开始进化了。
肺鱼的最早代表是泥盆纪中期的双鳍鱼。在此基础上，肺鱼类在晚泥盆世至石炭纪曾经比较繁盛，至今只有少数极特化的代表生活在非洲、澳洲和南美洲的赤道地区，可以说是一种“活化石”。
Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes
Heather M. King, Neil H. Shubin, Michael . Coates, and Melina E. Hale
Tetrapods evolved from sarcopterygian fishes in the Devonian and were the first vertebrates to colonize land. The locomotor component of this transition can be divided into four major events: terrestriality, the origins of digited limbs, solid substrate-based locomotion, and alternating gaits that use pelvic appendages as major propulsors. As the sister group to tetrapods, lungfish are a morphologically and phylogenetically relevant sarcopterygian taxon for understanding the order in which these events occurred. We found that a species of African lungfish (Protopterus annectens) uses a range of pelvic fin-driven, tetrapod-like gaits, including walking and bounding, in an aquatic environment, despite having a derived limb endoskeleton and primitively small, muscularly supported pelvis. Surprisingly, given these morphological traits, P. annectens also lifts its body clear of the substrate using its pelvic fins, an ability thought to be a tetrapod innovation. Our findings suggest that some fundamental features of tetrapod locomotion, including pelvic limb gait patterns and substrate association, probably arose in sarcopterygians before the origin of digited limbs or terrestriality. It follows that the attribution of some of the nondigited Devonian fossil trackways to limbed tetrapods may need to be revisited.
文献链接：https://www.pnas.org/content/108/52/21146.abstract?sid=b02d1bf1-0e42-45ec-a747-9f78df95b4aa
