來(lái)源：M. Friedman, University of Chicago and Field Museum
據(jù)4月17日的《科學(xué)》雜志報(bào)道說(shuō)，通過(guò)研究最早陸地動(dòng)物的古老的臂骨,，研究人員說(shuō),，他們已經(jīng)發(fā)現(xiàn)了某些差別，這些差別可以對(duì)我們所知的地球上最早的從海洋爬到陸地上生活的4腿動(dòng)物在進(jìn)化上的位置進(jìn)行重新排列,。
Viviane Callier及其同僚對(duì)我們星球上的最早的四足動(dòng)物進(jìn)行了仔細(xì)的觀察后發(fā)現(xiàn)，Ichthyostega（魚(yú)石螈）隨著它們年齡的增加，其上臂骨的位置會(huì)發(fā)生緩慢的變化,。 這一發(fā)現(xiàn)表明,，在它們的整個(gè)生命歷程中，其上臂發(fā)生了功能性的變化,，而且Ichthyostega 在年幼的時(shí)候會(huì)在水中生活更多的時(shí)間并在其生命的后期移往陸地之上,，這使得它們成為已知的最喜歡在水中生活的四足動(dòng)物。 過(guò)去,，研究人員相信Acanthostega（棘魚(yú)石螈）是在化石記錄中最像魚(yú)的陸地動(dòng)物,，但這一有關(guān)Ichthyostega 遷徙前肢的新發(fā)現(xiàn)表明，Ichthyostega 應(yīng)該在進(jìn)化樹(shù)上占有一個(gè)更基底的位置,，而其它的種系（如Acanthostega）可能是從Ichthyostega 所進(jìn)化而來(lái),，而非反過(guò)來(lái)的情景。 研究人員總結(jié)說(shuō),，他們已經(jīng)捕捉到了在水生環(huán)境到陸地環(huán)境之間發(fā)育轉(zhuǎn)變的最老的化石證據(jù),。 Matt Friedman在一篇Perspective中對(duì)這些發(fā)現(xiàn)進(jìn)行了更詳細(xì)的解釋。（生物谷Bioon.com）
生物谷推薦原始出處：
Science 17 April 2009:DOI: 10.1126/science.1167542
Contrasting Developmental Trajectories in the Earliest Known Tetrapod Forelimbs
Viviane Callier,1* Jennifer A. Clack,1 Per E. Ahlberg2
Ichthyostega and Acanthostega are the earliest tetrapods known from multiple near-complete skeletons, with Acanthostega generally considered the more primitive. New material indicates differing ontogenetic trajectories for their forelimbs: In Ichthyostega, the pattern of muscle attachment processes on small humeri (upper arm bones) resembles that in "fish" members of the tetrapod stem group such as Tiktaalik, whereas large humeri approach (but fail to attain) the tetrapod crown-group condition; in Acanthostega, both small and large humeri exhibit the crown-group pattern. We infer that Ichthyostega underwent greater locomotory terrestrialization during ontogeny. The newly recognized primitive characteristics also suggest that Ichthyostega could be phylogenetically more basal than Acanthostega.
1 University Museum of Zoology Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
2 Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Evolutionary Biology Centre, Uppsala University, Norbyv?gen 18A, 752 36 Uppsala, Sweden.
