早期的假设认为，四足动物（陆地脊椎动物）的足趾与鱼类的放射鳍同源，但根据发育研究结果，同时根据一种名叫“潘氏鱼”、与陆地脊椎动物密切相关的目前已经灭绝的鱼（这种鱼似乎没有末梢的趾状放射鳍）的鳍，这一观点似乎并不可靠。关于鱼类在它们演化史早期有同源足趾的证据很多，但“潘氏鱼”成为完全接受这一观点的一个障碍。现在，对一个经典“潘氏鱼”标本所做的一项电脑断层摄影（CT）研究表明，过去的解释是错误的，这种鱼的确有趾状放射鳍：进入鱼指（fish fingers）时代的大门已经打开。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 456, 636-638 (4 December 2008) | doi:10.1038/nature07339
The pectoral fin of Panderichthys and the origin of digits
Catherine A. Boisvert1, Elga Mark-Kurik2 & Per E. Ahlberg1
1 Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Evolutionary Biology Centre, Uppsala University, Norbyv?gen 18A, 752 36 Uppsala, Sweden
2 Institute of Geology at Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia
One of the identifying characteristics of tetrapods (limbed vertebrates) is the presence of fingers and toes. Whereas the proximal part of the tetrapod limb skeleton can easily be homologized with the paired fin skeletons of sarcopterygian (lobe-finned) fish, there has been much debate about the origin of digits. Early hypotheses1 interpreted digits as derivatives of fin radials, but during the 1990s the idea gained acceptance that digits are evolutionary novelties without direct equivalents in fish fin skeletons. This was partly based on developmental genetic data2, but also substantially on the pectoral fin skeleton of the elpistostegid (transitional fish/tetrapod) Panderichthys, which appeared to lack distal digit-like radials3. Here we present a CT scan study of an undisturbed pectoral fin of Panderichthys demonstrating that the plate-like 'ulnare' of previous reconstructions is an artefact and that distal radials are in fact present. This distal portion is more tetrapod-like than that found in Tiktaalik 4 and, in combination with new data about fin development in basal actinopterygians5, sharks6 and lungfish7, makes a strong case for fingers not being a novelty of tetrapods but derived from pre-existing distal radials present in all sarcopterygian fish.
