Cretaceous choristoderan reptiles gave birth to live young |
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Authors: | Qiang Ji Xiao-chun Wu Yen-nien Cheng |
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Institution: | (1) Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037, China;(2) Canadian Museum of Nature, P.O. Box 3443 STN ‘D’, Ottawa, ON, K1P 6P4, Canada;(3) National Museum of Natural Science, 1 Kuan Chien Road, Taichung, 404, Taiwan, China; |
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Abstract: | Viviparity (giving birth to live young) in fossil reptiles has been known only in a few marine groups: ichthyosaurs, pachypleurosaurs,
and mosasaurs. Here, we report a pregnant specimen of the Early Cretaceous Hyphalosaurus baitaigouensis, a species of Choristodera, a diapsid group known from unequivocal fossil remains from the Middle Jurassic to the early Miocene
(about 165 to 20 million years ago). This specimen provides the first evidence of viviparity in choristoderan reptiles and
is also the sole record of viviparity in fossil reptiles which lived in freshwater ecosystems. This exquisitely preserved
specimen contains up to 18 embryos arranged in pairs. Size comparison with small free-living individuals and the straight
posture of the posterior-most pair suggest that those embryos were at term and had probably reached parturition. The posterior-most
embryo on the left side has the head positioned toward the rear, contrary to normal position, suggesting a complication that
may have contributed to the mother’s death. Viviparity would certainly have freed species of Hyphalosaurus from the need to return to land to deposit eggs; taking this advantage, they would have avoided intense competition with
contemporaneous terrestrial carnivores such as dinosaurs. |
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