Egg size and structure reflect important constraints on the reproductive and life-history characteristics of vertebrates 1 . More than two-thirds of all extant amniotes lay eggs 2 . During the Mesozoic era (around 250 million to 65 million years ago), body sizes reached extremes; nevertheless, the largest known egg belongs to the only recently extinct elephant bird 3 , which was roughly 66 million years younger than the last nonavian dinosaurs and giant marine reptiles. Here we report a new type of egg discovered in nearshore marine deposits from the Late Cretaceous period (roughly 68 million years ago) of Antarctica. It exceeds all nonavian dinosaur eggs in volume and differs from them in structure. Although the elephant bird egg is slightly larger, its eggshell is roughly five times thicker and shows a substantial prismatic layer and complex pore structure 4 . By contrast, the new fossil, visibly collapsed and folded, presents a thin eggshell with a layered structure that lacks a prismatic layer and distinct pores, and is similar to that of most extant lizards and snakes (Lepidosauria) 5 . The identity of the animal that laid the egg is unknown, but these preserved morphologies are consistent with the skeletal remains of mosasaurs (large marine lepidosaurs) found nearby. They are not consistent with described morphologies of dinosaur eggs of a similar size class. Phylogenetic analyses of traits for 259 lepidosaur species plus outgroups suggest that the egg belonged to an individual that was at least 7 metres long, hypothesized to be a giant marine reptile, all clades of which have previously been proposed to show live birth 6 . Such a large egg with a relatively thin eggshell may reflect derived constraints associated with body shape, reproductive investment linked with gigantism, and lepidosaurian viviparity, in which a ‘vestigial’ egg is laid and hatches immediately 7 . A fossil egg unearthed from Cretaceous deposits in Antarctica is more than 20 cm long, exceeds all known nonavian eggs in volume, is soft-shelled, and was perhaps laid by a giant marine lizard such as a mosasaur.

中文翻译：

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来自南极洲晚白垩世的巨大软壳蛋

卵的大小和结构反映了对脊椎动物 1 的生殖和生活史特征的重要限制。超过三分之二的现存羊膜动物会产卵 2 。在中生代（大约 2.5 亿至 6500 万年前），体型达到了极限；尽管如此，已知最大的蛋属于最近唯一灭绝的象鸟 3 ，它比最后的非鸟类恐龙和巨型海洋爬行动物大约年轻 6600 万年。在这里，我们报告了在南极洲白垩纪晚期（大约 6800 万年前）的近岸海洋沉积物中发现的一种新型蛋。它在体积上超过了所有非鸟类恐龙蛋，并且在结构上与它们不同。虽然象鸟蛋稍微大点，它的蛋壳大约厚五倍，并显示出大量棱柱形层和复杂的孔隙结构 4 。相比之下，新化石明显塌陷和折叠，呈薄蛋壳，具有分层结构，缺乏棱柱形层和明显的孔隙，与大多数现存的蜥蜴和蛇类（鳞龙目） 5 相似。产卵动物的身份不明，但这些保存下来的形态与附近发现的沧龙（大型海洋鳞龙）的骨骼遗骸一致。它们与描述的大小相似的恐龙蛋的形态不一致。对 259 种鳞龙物种加上外群的特征的系统发育分析表明，这个蛋属于一个至少 7 米长的个体，被假设为一种巨大的海洋爬行动物，所有进化枝以前都被提议显示活产 6 . 如此大的蛋壳相对较薄，这可能反映了与体型、与巨人症相关的生殖投资和鳞龙类胎生相关的衍生限制，在这种情况下，产下“残留”蛋并立即孵化 7 。从南极洲白垩纪沉积物中出土的化石蛋长 20 多厘米，体积超过所有已知的非鸟类蛋，是软壳的，可能是由沧龙等巨型海洋蜥蜴产下的。