The hand of birds revealed by early ostrich embryos
The hand of birds revealed by early ostrich embryos
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DOI：
10.1007/s00114-002-0350-y
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发表时间：
2002-09-01
影响因子：
--
通讯作者：
Nowicki, J
中科院分区：
文献类型：
--
作者：
Feduccia, A;Nowicki, J
解决鸟类手指同源性的问题被认为是古生物学证据和胚胎学证据之间的冲突，前者被认为支持由第I、II、III手指组成的手，因为已知最早的鸟类始祖鸟的指骨公式与中生代的五趾祖龙的指骨公式相似，而胚胎学证据传统上支持第II、III、IV手指。我们已经确定了原始鸟类鸵鸟骨骼主要特征的关键发育期。对鸟类手的趾原基的分析揭示了趾/掌骨I和V的原基，从而证实了先前的胚胎学研究，该研究间接地表明鸟类手包括趾II、III、IV，并且是连续的五趾动物。鸟类三趾手的趾的身份首次提出于1821年，并且从那时起就一直存在激烈的争论（Meckel 1821; Holmgren 1955）。早期的鸟类胚胎有三个中央的数字浓缩和浓缩的减少数字/掌骨V在发展后期消失，通常是一个浓缩的数字/掌骨I是缺席。通过孵化，制备和比较古颌鸟类，鸵鸟的括号内的胚胎，我们确定了关键时期的数字原质，提供了第一个直接和可证明的证据，以支持以前的胚胎学研究，暗示鸟类的手包括数字II，III，IV（伯克和Feduccia。一九九七年;新颚类和古颚类鸟类之间的深刻分歧是由来自蒙古和中国的古颚类Ambiortus和Otogomis的早白垩世化石证明的（Kurochkin 1999）。因为古颌类是最有可能的原始鸟类，它们的胚胎学提供了一个机会来检验骨骼同源性的假设，这些假设被其他分类群中的衍生修饰所掩盖。
The problem of resolving the homology of the digits of the avian hand has been framed as a conflict between paleontological and embryological evidence, the former thought to support a hand composed of digits I, II, III, because of similarity of the phalangeal formulae of the earliest known bird Archaeopteryx to that of Mesozoic pentadactyl archosaurs, while embryological evidence has traditionally favored a II, III, IV avian hand. We have identified the critical developmental period for the major features of the avian skeleton in a primitive bird, the ostrich. Analysis of digit anlagen in the avian hand has revealed those for digits/metacarpals I and V, thus confirming previous embryological studies that indirectly suggested that the avian hand comprises digits II, III, IV, and was primitively pentadactyl.The identity of the digits of the avian tridactyl hand was first addressed in 1821 and has been hotly debated since then (Meckel 1821; Holmgren 1955). Early avian embryos have three central digital condensations and a condensation for a reduced digit/metacarpal V which disappears late in development; typically a condensation for digit/metacarpal I is absent. By incubating, preparing and comparing bracketed embryos of a paleognathous bird, the ostrich, we identified the critical period for digital anlagen, providing the first direct and demonstrable evidence to support previous embryological studies that implied that the avian hand comprises digits II, III, IV (Burke and Feduccia. 1997; Hinchliffe 1997).A deep split between neognathous and paleognathous birds is evidenced by Lower Cretaceous fossils of the paleognaths Ambiortus and Otogomis from Mongolia and China (Kurochkin 1999). Because paleognaths are the most likely primitive living birds, their embryology presents an opportunity to test hypotheses of skeletal homology obscured by derived modifications in other taxa.