Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs.
Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs.
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DOI：
10.1371/journal.pone.0142829
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发表时间：
2015
期刊：
影响因子：
3.7
通讯作者：
Therrien F
中科院分区：
文献类型：
--
作者：
Tanaka K;Zelenitsky DK;Therrien F
了解恐龙建造的巢穴类型可以深入了解祖龙筑巢和繁殖行为的进化。然而，它们的筑巢材料和筑巢结构的保存潜力很低，这意味着大多数信息只能通过与现存的祖龙进行比较来间接收集。在现存的主龙类中，有两种常见的巢型：1）有盖巢，蛋在完全被筑巢材料覆盖的情况下孵化（如鳄类和大足类）; 2）开放巢，蛋暴露在巢中孵化（如大多数鸟类）。以前，恐龙巢穴类型是通过估计水蒸气传导率来推断的（即，扩散能力），其基础上的前提下，高电导率对应于覆盖的巢和低电导率开放的巢。然而，这种方法缺乏统计上的严谨性和不一致性，使其应用成问题，其有效性值得怀疑。作为一种替代方案，我们提出了一个严格的统计方法来推断巢型的蛋壳孔隙度和蛋质量的大型数据集的基础上编译超过120现存的祖龙物种和29祖龙灭绝类群/卵类群。蛋壳孔隙度和巢型之间存在着很强的相关性，在现存的祖龙表明，蛋壳孔隙度可以作为一个代理巢型，因此判别分析可以帮助预测巢型灭绝类群。我们的研究结果表明：1）有盖的巢可能是恐龙（可能也是祖龙）的原始状态，2）开放的巢首先在非鸟类的兽脚类恐龙中进化，比卢林汉龙更进化，并且可能在非鸟类的手盗龙中广泛存在，远在鸟类出现之前。虽然埋藏学证据表明，基底开放巢（即，虽然盗蛋龙和伤齿龙可能是最早孵卵的恐龙，但它们仍然将部分卵埋在沉积物中。只有在真鸟类中，开放的巢中的蛋才能完全暴露。手盗龙类的开放巢和育雏行为的潜在共同进化可能使兽脚亚目恐龙摆脱了覆盖巢所固有的地面限制，并允许利用其他筑巢地点。因此，这些筑巢方式和行为的变化可能在手盗龙（包括鸟类）的进化成功中发挥了作用。
Knowledge about the types of nests built by dinosaurs can provide insight into the evolution of nesting and reproductive behaviors among archosaurs. However, the low preservation potential of their nesting materials and nesting structures means that most information can only be gleaned indirectly through comparison with extant archosaurs. Two general nest types are recognized among living archosaurs: 1) covered nests, in which eggs are incubated while fully covered by nesting material (as in crocodylians and megapodes), and 2) open nests, in which eggs are exposed in the nest and brooded (as in most birds). Previously, dinosaur nest types had been inferred by estimating the water vapor conductance (i.e., diffusive capacity) of their eggs, based on the premise that high conductance corresponds to covered nests and low conductance to open nests. However, a lack of statistical rigor and inconsistencies in this method render its application problematic and its validity questionable. As an alternative we propose a statistically rigorous approach to infer nest type based on large datasets of eggshell porosity and egg mass compiled for over 120 extant archosaur species and 29 archosaur extinct taxa/ootaxa. The presence of a strong correlation between eggshell porosity and nest type among extant archosaurs indicates that eggshell porosity can be used as a proxy for nest type, and thus discriminant analyses can help predict nest type in extinct taxa. Our results suggest that: 1) covered nests are likely the primitive condition for dinosaurs (and probably archosaurs), and 2) open nests first evolved among non-avian theropods more derived than Lourinhanosaurus and were likely widespread in non-avian maniraptorans, well before the appearance of birds. Although taphonomic evidence suggests that basal open nesters (i.e., oviraptorosaurs and troodontids) were potentially the first dinosaurs to brood their clutches, they still partially buried their eggs in sediment. Open nests with fully exposed eggs only became widespread among Euornithes. A potential co-evolution of open nests and brooding behavior among maniraptorans may have freed theropods from the ground-based restrictions inherent to covered nests and allowed the exploitation of alternate nesting locations. These changes in nesting styles and behaviors thus may have played a role in the evolutionary success of maniraptorans (including birds).