Blackburn Daniel G, Sidor Christian A
Department of Biology and Electron Microscopy Center, Trinity College, Hartford, CT, USA.
Int J Dev Biol. 2014;58(10-12):935-48. doi: 10.1387/ijdb.150087db.
Although viviparity (live-bearing reproduction) is widely distributed among lizards and snakes, it is entirely absent from other extant Reptilia and many extinct forms. However, paleontological evidence reveals that viviparity was present in at least nine nominal groups of pre-Cenozoic reptiles, representing a minimum of six separate evolutionary origins of this reproductive mode. Two viviparous clades (sauropterygians and ichthyopterygians) lasted more than 155 million years, a figure that rivals the duration of mammalian viviparity. Circumstantial evidence indicates that extinct viviparous reptiles had internal fertilization, amniotic fetal membranes, and placentas that sustained developing embryos via provision of respiratory gases, water, calcium, and possibly organic nutrients. Production of offspring via viviparity facilitated the invasion of marine habitats in at least five reptilian lineages. Thus, this pattern of embryonic development and reproduction was central to the ecology and evolution of these ancient animals, much as it is to numerous extant species of vertebrates.
尽管胎生（活体繁殖）在蜥蜴和蛇类中广泛存在，但在其他现存爬行动物以及许多已灭绝的类群中却完全不存在。然而，古生物学证据表明，胎生在至少九个前新生代爬行动物的分类群中出现过，这代表了这种繁殖方式至少有六个独立的进化起源。两个胎生分支（鳍龙超目和鱼龙超目）延续了超过1.55亿年，这一数字可与哺乳动物胎生的持续时间相媲美。间接证据表明，已灭绝的胎生爬行动物具有体内受精、羊膜胎膜和胎盘，这些胎盘通过提供呼吸气体、水、钙以及可能的有机营养物质来维持发育中的胚胎。通过胎生产仔促进了至少五个爬行动物谱系对海洋栖息地的入侵。因此，这种胚胎发育和繁殖模式对于这些古代动物的生态和进化至关重要，就像它对众多现存脊椎动物物种一样重要。
