Department of Biology and Electron Microscopy Center, Trinity College, Hartford, Connecticut, USA.
Department of Biological Sciences, East Tennessee State University, Johnson City, Tennessee, USA.
J Morphol. 2021 Jul;282(7):1024-1046. doi: 10.1002/jmor.21320. Epub 2021 Jan 12.
Evolution of the terrestrial egg of amniotes (reptiles, birds, and mammals) is often considered to be one of the most significant events in vertebrate history. Presence of an eggshell, fetal membranes, and a sizeable yolk allowed this egg to develop on land and hatch out well-developed, terrestrial offspring. For centuries, morphologically-based studies have provided valuable information about the eggs of amniotes and the embryos that develop from them. This review explores the history of such investigations, as a contribution to this special issue of Journal of Morphology, titled Developmental Morphology and Evolution of Amniote Eggs and Embryos. Anatomically-based investigations are surveyed from the ancient Greeks through the Scientific Revolution, followed by the 19th and early 20th centuries, with a focus on major findings of historical figures who have contributed significantly to our knowledge. Recent research on various aspects of amniote eggs is summarized, including gastrulation, egg shape and eggshell morphology, eggs of Mesozoic dinosaurs, sauropsid yolk sacs, squamate placentation, embryogenesis, and the phylotypic phase of embryonic development. As documented in this review, studies on amniote eggs and embryos have relied heavily on morphological approaches in order to answer functional and evolutionary questions.
羊膜动物（爬行动物、鸟类和哺乳动物）的陆生卵的演化通常被认为是脊椎动物历史上最重要的事件之一。蛋壳、胎膜和大量蛋黄的存在使这种卵能够在陆地上发育，并孵化出发育良好的陆生后代。几个世纪以来，基于形态的研究为羊膜动物的卵及其胚胎的发育提供了有价值的信息。本综述探讨了这些研究的历史，作为对本期《形态学杂志》特刊的贡献，特刊题为“羊膜动物卵和胚胎的发育形态学和演化”。本文从古希腊人开始，对基于解剖学的研究进行了调查，一直追溯到科学革命、19 世纪和 20 世纪早期，重点介绍了对我们的知识有重大贡献的历史人物的主要发现。总结了关于羊膜动物卵的各个方面的最新研究，包括原肠胚形成、卵的形状和卵壳形态、中生代恐龙的卵、蜥形类的卵黄囊、有鳞目胎盘、胚胎发生以及胚胎发育的表型阶段。正如本综述所记录的，对羊膜动物卵和胚胎的研究主要依赖于形态学方法，以回答功能和进化问题。
