WERE ALL PTEROSAURS OVIPAROUS?
Much progress has been made recently in understanding pterosaurs, Mesozoic flying reptiles, and some basic aspects of their palaeobiology, phylogenetic relationships and evolutionary history are now generally agreed upon. Studies of pterosaur reproductive biology have been kick-started by the discovery of three eggs, with embryos, each apparently representing a different species of pterosaur. Two finds in the Lower Cretaceous Yixian Formation of China belong to pterodactyloids and in one case can be confidently assigned to the Ornithocheiridae on the basis of distinctive proportions of the limb bones (such as the relatively short third metatarsal and the relatively long fore- limb), and morphological features including the warped deltopectoral crest of the humerus. A third embryo from the Lower Cretaceous of Loma del Pterodaustro in Argentina compares extremely closely to hatchlings and older individuals of Pterodaustro guinazui, the only pterosaur known from this site, and undoubtedly belongs to this species. Several lines of evidence support the idea that oviparity was universal in pterosaurs: (1) oviparity in ctenochasmatids and ornithocheirids suggests, as a minimum inference, that all pterodactyloids, at least, were oviparous; (2) oviparity is widespread in diapsids and, irrespective of the exact location of Pterosauria within this clade (currently much debated), oviparity in pterosaur ancestors is much more likely than viviparity, especially if pterosaurs prove to be ornithodirans; (3) the complete absence of any evidence, so far, for viviparity in pterosaurs. The likelihood that they had a poorly calcified, or possibly even non-calcified pliable or parchment-shelled egg is probably the main reason why pterosaur eggs are so rare compared to those of other groups such as dinosaurs and birds, which have well calcified hard shells.
David M. Unwin Lu Junchang D. Charles Deeming
Institut fur Palaontologie, Museum fur Naturkunde, Humboldt Universitat zu Berlin, Invalidenstra Be Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Hatchery Consulting and Research, 9 Eagle Drive, Welton, Lincoln, Lincolnshire LN2 3LP, United Kingd
国际会议
2005·河源国际恐龙学术研讨会(2005 Heyuan International Dinosaur Symposium)
广东河源
英文
141-167
2005-04-08（万方平台首次上网日期，不代表论文的发表时间）