早期的假設(shè)認(rèn)為，四足動物（陸地脊椎動物）的足趾與魚類的放射鰭同源,，但根據(jù)發(fā)育研究結(jié)果,，同時(shí)根據(jù)一種名叫“潘氏魚”、與陸地脊椎動物密切相關(guān)的目前已經(jīng)滅絕的魚（這種魚似乎沒有末梢的趾狀放射鰭）的鰭,，這一觀點(diǎn)似乎并不可靠,。關(guān)于魚類在它們演化史早期有同源足趾的證據(jù)很多，但“潘氏魚”成為完全接受這一觀點(diǎn)的一個(gè)障礙?，F(xiàn)在,，對一個(gè)經(jīng)典“潘氏魚”標(biāo)本所做的一項(xiàng)電腦斷層攝影（CT）研究表明，過去的解釋是錯(cuò)誤的,，這種魚的確有趾狀放射鰭：進(jìn)入魚指（fish fingers）時(shí)代的大門已經(jīng)打開,。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
