Research press release


Nature Communications

Fossils: Ancient reptile gave birth to live young



今回、Jun Liuの研究チームは、首の長い水生爬虫類のディノケファロサウルスの化石標本が中国で新たに発見され、その年代が三畳紀中期と決定されたことを説明している。これはディノケファロサウルスの成体の化石であり、その腹部には発生が進んだ胚が保存されており、胎生の証拠となっている。この知見は、主竜様類全体において胎生に対する障害のないことを示唆している。


A fossil of a pregnant reptile from approximately 245 million years ago is described in Nature Communications this week. This discovery indicates that this archosauromorph reptile, which belongs to the same group as dinosaurs, birds and crocodilians, gave birth to live young rather than laying eggs. Live birth was previously not known in any archosauromorph.

Live birth has evolved independently in many types of animals. However, modern birds and crocodilians all reproduce by laying eggs, which has suggested a biological constraint preventing live birth in this lineage.

Jun Liu and colleagues describe a new fossil specimen of Dinocephalosaurus, a long-necked, aquatic reptile found in China and dating from the Middle Triassic. A developmentally advanced embryo is preserved within the abdomen of the adult Dinocephalosaurus, providing evidence of live birth. This finding suggests that there is no general impediment against live birth in the archosauramorphs.

Analysis of the evolutionary history of Dinocephalosaurus indicates that the sex of offspring was determined genetically. This differs from related species, such as crocodilians and some turtles, in which the sex is determined by temperature. The authors conclude that genetic sex determination may have been a precondition for live birth in Dinocephalosaurus, since internal body temperature regulation is not compatible with temperature-dependent sex determination.

doi: 10.1038/ncomms14445

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