盾皮鱼是一大类原始有甲鱼类。虽然完全灭绝,但它们神秘的解剖体系有可能含有关于有颌类脊椎动物、包括我们人类自己演化历史的线索。一个新的化石发现,澄清了关于Incisoscutum的生殖机制的问题。
Incisoscutum作为节颈鱼家族(一个大而重要的盾皮鱼类别)的一个成员尤为研究人员所感兴趣。研究人员最近发现了一只成年Incisoscutum ritcchiei雌性个体的一个保存完好的化石,它含有胚胎,这是体内受精的证据。而新发现的化石是该物种的一个雄性个体,长有阴茎一样的交脚器,与化石褶齿鱼(一类未披甲的盾皮鱼)和鲨鱼中所见的相似。(生物谷Bioon.com)
生物谷推荐原始出处:
Nature 460, 888-889 (13 August 2009) | doi:10.1038/nature08176
Pelvic claspers confirm chondrichthyan-like internal fertilization in arthrodires
Per Ahlberg1, Kate Trinajstic2,3,4, Zerina Johanson5 & John Long6,7,8
1 Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Uppsala University, Norbyv?gen 18A, 752 36 Uppsala, Sweden
2 Western Australian Organic and Isotope Geochemistry Centre, Department of Applied Chemistry, Curtin University, Perth, Western Australia 6102, Australia
3 Earth and Planetary Sciences, Western Australian Museum, Perth, Western Australia 6000, Australia
4 School of Earth and Environment, The University of Western Australia, Perth, Western Australia 6009, Australia
5 Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK
6 Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia
7 Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital Territory 2600,
8 School of Geosciences, Monash University, Clayton, Victoria 3800, Australia
Recent finds1, 2 demonstrate that internal fertilization and viviparity (live birth) were more widespread in the Placodermi, an extinct group of armoured fishes, than was previously realized. Placoderms represent the sister group of the crown group jawed vertebrates (Gnathostomata)3, 4, making their mode(s) of reproduction potentially informative about primitive gnathostome conditions. An ossified pelvic fin basipterygium discovered in the arthrodire Incisoscutum ritchiei was hypothesized to be identical in males and females, with males presumed to have an additional cartilaginous element or series forming a clasper. Here we report the discovery of a completely ossified pelvic clasper in Incisoscutum ritchiei (WAM 03.3.28) which shows that this interpretation was incorrect: the basipterygium described previously1 is in fact unique to females. The male clasper is a slender rod attached to a square basal plate that articulates directly with the pelvis. It carries a small cap of dermal bone covered in denticles and small hooks that may be homologous with the much larger dermal component of the ptyctodont clasper.