![]() "EER is common and variable in lizards and snakes today. "Other fossils, including a choristodere from the Cretaceous of China, described here, show the to-and-fro between oviparity and viviparity happened in other groups, not just in lizards."ĭr Joseph Keating explained: "EER is widespread among vertebrates today, where the developing young are retained by the mother for a lesser or greater span of time. "Also, when we look at fossils, we find that many of them were live-bearers, including the Mesozoic marine reptiles like ichthyosaurs and plesiosaurs," said Dr Armin Elsler. "Sometimes, closely related species show both behaviours, and it turns out that live-bearing lizards can flip back to laying eggs much more easily than had been assumed." Biologists had noticed many lizards and snakes display flexible reproductive strategy across oviparity and viviparity. Project Leader Professor Baoyu Jiang added: "This standard view has been challenged. It was said to be a 'private pond' in which the developing reptile was protected from drying out in the warm climates and enabled the Amniota to move away from the waterside and dominate terrestrial ecosystems." "When the amniotes came on the scene 320 million years ago, they were able to break away from the water by evolving waterproof skin and other ways to control water loss. They had to live in or near water to feed and breed, as in modern amphibians such as frogs and salamanders. Professor Michael Benton from the Bristol's School of Earth Sciences explained: "Before the amniotes, the first tetrapods to evolve limbs from fishy fins were broadly amphibious in habits. While the hard-shelled egg has often been seen as one of the greatest innovations in evolution, this research implies it was EER that gave this particular group of animals the ultimate protection. ![]() ![]() The findings, published today in Nature Ecology & Evolution, show that all the great evolutionary branches of Amniota, namely Mammalia, Lepidosauria (lizards and relatives), and Archosauria (dinosaurs, crocodilians, birds) reveal viviparity and extended embryo retention in their ancestors.Įxtended embryo retention (EER) is when the young are retained by the mother for a varying amount of time, likely depending on when conditions are best for survival. However, a fresh study of 51 fossil species and 29 living species which could be categorised as oviparous (laying hard or soft-shelled eggs) or viviparous (giving birth to live young) suggests otherwise. If you can't access the full text you can try requesting it through interlibrary loan.Until now, the hard-shelled egg was thought to be the key to the success of the amniotes - a group of vertebrates that undergo embryonic or fetal development within an amnion, a protective membrane inside the egg.Its better to have a saved copy than to lose access when it comes time to write the paper. Sometimes if things are picked up by the popular press, publishers will open up the scientific article for a while.Did you download a copy of the scientific article?.don't select an article that is about how animals help people)? Is your scientific article mainly about the animal (e.g.Science Daily and posts press releases, do not use a post from these sites.The audience for the article to be the general public (not journalists or scientists).Are you sure your popular science article is NOT a press release?.Does the popular science article describe the research in enough depth for you to make a comparison?. ![]()
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