Wiemann Jasmina, Yang Tzu-Ruei, Sander Philipp N, Schneider Marion, Engeser Marianne, Kath-Schorr Stephanie, Müller Christa E, Sander P Martin
Division of Palaeontology, Steinmann Institute of Geology, Mineralogy and Palaeontology, University of Bonn, Bonn, Germany.
Department of Geology & Geophysics, Yale University, New Haven, CT, United States of America.
PeerJ. 2017 Aug 29;5:e3706. doi: 10.7717/peerj.3706. eCollection 2017.
Protoporphyrin (PP) and biliverdin (BV) give rise to the enormous diversity in avian egg coloration. Egg color serves several ecological purposes, including post-mating signaling and camouflage. Egg camouflage represents a major character of open-nesting birds which accomplish protection of their unhatched offspring against visually oriented predators by cryptic egg coloration. Cryptic coloration evolved to match the predominant shades of color found in the nesting environment. Such a selection pressure for the evolution of colored or cryptic eggs should be present in all open nesting birds and relatives. Many birds are open-nesting, but protect their eggs by continuous brooding, and thus exhibit no or minimal eggshell pigmentation. Their closest extant relatives, crocodiles, protect their eggs by burial and have unpigmented eggs. This phylogenetic pattern led to the assumption that colored eggs evolved within crown birds. The mosaic evolution of supposedly avian traits in non-avian theropod dinosaurs, however, such as the supposed evolution of partially open nesting behavior in oviraptorids, argues against this long-established theory. Using a double-checking liquid chromatography ESI-Q-TOF mass spectrometry routine, we traced the origin of colored eggs to their non-avian dinosaur ancestors by providing the first record of the avian eggshell pigments protoporphyrin and biliverdin in the eggshells of Late Cretaceous oviraptorid dinosaurs. The eggshell parataxon can be assigned to the oviraptor based on exceptionally preserved, late developmental stage embryo remains. The analyzed eggshells are from three Late Cretaceous fluvial deposits ranging from eastern to southernmost China. Reevaluation of these taphonomic settings, and a consideration of patterns in the porosity of completely preserved eggs support an at least partially open nesting behavior for oviraptorosaurs. Such a nest arrangement corresponds with our reconstruction of blue-green eggs for oviraptors. According to the sexual signaling hypothesis, the reconstructed blue-green eggs support the origin of previously hypothesized avian paternal care in oviraptorid dinosaurs. Preserved dinosaur egg color not only pushes the current limits of the vertebrate molecular and associated soft tissue fossil record, but also provides a perspective on the potential application of this unexplored paleontological resource.
原卟啉（PP）和胆绿素（BV）导致了鸟类蛋颜色的巨大多样性。蛋的颜色具有多种生态功能，包括交配后的信号传递和伪装。蛋的伪装是开放式筑巢鸟类的一个主要特征，它们通过隐秘的蛋颜色来保护未孵化的后代免受视觉导向的捕食者的侵害。隐秘的颜色进化为与筑巢环境中占主导地位的颜色阴影相匹配。这种对有颜色或隐秘蛋进化的选择压力应该存在于所有开放式筑巢鸟类及其近亲中。许多鸟类是开放式筑巢的，但通过持续孵卵来保护它们的蛋，因此蛋壳色素沉着很少或没有。它们现存的近亲鳄鱼，通过掩埋来保护它们的蛋，并且蛋没有色素。这种系统发育模式导致了这样一种假设，即有颜色的蛋是在冠群鸟类中进化而来的。然而，非鸟类兽脚亚目恐龙中所谓鸟类特征的镶嵌进化，比如窃蛋龙类中部分开放式筑巢行为的假定进化，与这个长期确立的理论相悖。通过使用一种双重检查的液相色谱电喷雾串联四极杆飞行时间质谱程序，我们通过在晚白垩世窃蛋龙类恐龙的蛋壳中首次记录鸟类蛋壳色素原卟啉和胆绿素，追踪了有颜色的蛋的起源至它们的非鸟类恐龙祖先。基于保存异常完好的晚期发育阶段胚胎遗骸，蛋壳副分类单元可被归为窃蛋龙。分析的蛋壳来自中国东部到最南端的三个晚白垩世河流沉积层。对这些埋藏学环境的重新评估，以及对完全保存的蛋的孔隙率模式的考虑，支持窃蛋龙至少有部分开放式筑巢行为。这样的巢的安排与我们对窃蛋龙蓝绿色蛋的重建相符。根据性信号假说，重建的蓝绿色蛋支持了之前假设的窃蛋龙类恐龙中鸟类父性照料的起源。保存下来的恐龙蛋颜色不仅突破了目前脊椎动物分子及相关软组织化石记录的极限，还为这种未被探索的古生物学资源的潜在应用提供了一个视角。
