最近關(guān)于褶齒魚(yú)類（被稱為“盾皮魚(yú)”的已滅絕化石魚(yú)的一個(gè)小類別）能夠進(jìn)行體內(nèi)受精和胎生的證據(jù)的發(fā)現(xiàn)，為我們了解生殖生物學(xué)的一種遠(yuǎn)古形式提供了一個(gè)難得的機(jī)會(huì),。
現(xiàn)在,，研究人員在另一種“盾皮魚(yú)”——“Incisoscutum”保存完好的化石內(nèi)也發(fā)現(xiàn)了胚胎。這個(gè)發(fā)現(xiàn)很重要,，因?yàn)?ldquo;Incisoscutum”是“節(jié)頸類”（“盾皮魚(yú)”的一個(gè)多樣化的大類別）的一個(gè)成員,。這些發(fā)現(xiàn)表明，“Incisoscutum”的骨盆帶發(fā)生了適應(yīng)性變化,，以支持用于體內(nèi)受精的鯊魚(yú)“鰭腳”等器官,。這些新的發(fā)現(xiàn)證實(shí)，體內(nèi)受精和胎生方式在最早的有顎類脊椎動(dòng)物中要比人們以前所認(rèn)為的普遍得多,。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 457, 1124-1127 (26 February 2009) | doi:10.1038/nature07732
Devonian arthrodire embryos and the origin of internal fertilization in vertebrates
John A. Long1,2,3, Kate Trinajstic4 & Zerina Johanson5
1 Museum Victoria, PO Box 666, Melbourne 3001, Victoria, Australia
2 Research School of Earth Sciences, The Australian National University, Canberra 2600, Australian Capital Territory, Australia
3 School of Geosciences, Monash University, Clayton 3800, Victoria, Australia
4 School of Earth and Geographical Sciences, The University of Western Australia, Perth 6009, Western Australia, Australia
5 Natural History Museum, Cromwell Road, London SW7 5BD, UK
Evidence of reproductive biology is extremely rare in the fossil record. Recently the first known embryos were discovered within the Placodermi1, an extinct class of armoured fish, indicating a viviparous mode of reproduction in a vertebrate group outside the crown-group Gnathostomata (Chondrichthyes and Osteichthyes). These embryos were found in ptyctodontids, a small group of placoderms phylogenetically basal to the largest group, the Arthrodira2, 3. Here we report the discovery of embryos in the Arthrodira inside specimens of Incisoscutum ritchiei from the Upper Devonian Gogo Formation of Western Australia4 (approximately 380 million years ago), providing the first evidence, to our knowledge, for reproduction using internal fertilization in this diverse group. We show that Incisoscutum and some phyllolepid arthrodires possessed pelvic girdles with long basipterygia that articulated distally with an additional cartilaginous element or series, as in chondrichthyans, indicating that the pelvic fin was used in copulation. As homology between similar pelvic girdle skeletal structures in ptyctodontids, arthrodires and chondrichthyans is difficult to reconcile in the light of current phylogenies of lower gnathostomes2, 3, 5, we explain these similarities as being most likely due to convergence (homoplasy). These new finds confirm that reproduction by internal fertilization and viviparity was much more widespread in the earliest gnathostomes than had been previously appreciated.
