分类： 生物学 >> 动物学 提交时间： 2019-08-27 合作期刊: 《古脊椎动物学报》
摘要： Molting—the process replacing one plumage with another—is a critically important biological function in Aves. This process annually replaces the feather coat, damaged by normal wear and tear, produces ontogenetic changes in feathering, and produces alternate breeding plumages associated with reproductive activity in adults. Immature, growing feathers are encased in a keratinous sheath, giving them a narrow, tubular, and featureless appearance. The complete loss of the sheath indicates the feather is mature. Despite the wealth of integumentary data published from the Jehol Biota, immature feathers have never been definitively reported, although they may potentially be preserved in a juvenile specimen of the non-avian oviraptorosaur theropod dinosaur Similicaudipteryx from the 120 Ma Jiufotang Formation. A developing feather has been reported in a 99 Ma enantiornithine neonate preserved in Burmese amber, in which three-dimensional preservation makes interpretations of integumentary structures more straightforward. Here we report on probable immature feathers in four juvenile enantiornithines (Aves: Ornithothoraces) from the Jehol Group. As observed in developing feathers in extant birds, the purported immature fossil feathers appear proximally narrow and featureless with barbs protruding only distally. Based on our observations, we suggest that similar-appearing feather structures preserved on the manus and tibiotarsus in the holotype of the enantiornithine Cruralispennia multidonta may alternatively be interpreted as immature feathers. The presence of immature feathers in combination with sexually dimorphic ornamental feathers in juvenile enantiornithines suggests the complex molting patterns of Neornithes, in which such ornaments only appear after several years (following several molts) when reproductive activity is achieved, are limited to a subset of crownward avians.
分类： 地球科学 >> 地质学 提交时间： 2017-08-10 合作期刊: 《古脊椎动物学报》
摘要： We provide a complete description of the skeletal anatomy of the holotype of Chiappeavis magnapremaxillo, the first enantiornithine to preserve a rectricial fan, suggesting that possibly rectricial bulbs were present in basal members of this clade. Notably, Chiappeavis preserves a primitive palatal morphology in which the vomers reach the premaxillae similar to Archaeopteryx but unlike the condition in the Late Cretaceous enantiornithine Gobipteryx. If rectricial bulbs were present, pengornithid pygostyle morphology suggests they were minimally developed. We estimate the lift generated by the tail fan preserved in this specimen and compare it to the tail fans preserved in other Early Cretaceous birds. Aerodynamic models indicate the tail of Chiappeavis produced less lift than that of sympatric ornithuromorphs. This information provides a possible explanation for the absence of widespread aerodynamic tail morphologies in the Enantiornithes. 契氏鸟(Chiappeavis)是首次发现保存有扇状尾羽的反鸟类，显示出尾羽球茎这一结构在较原始的反鸟类中已经发育。详细描述了巨前颌契氏鸟(C. magnapremaxillo)正型标本的骨骼形态学特征。契氏鸟的腭区形态与始祖鸟(Archaeopteryx)相似，而区别于晚白垩世的反鸟类戈壁鸟(Gobipteryx)。即使具有尾羽球茎，鹏鸟类的尾综骨形态也表明该结构发育较差。估算了在契氏鸟中由扇状尾羽所产生的浮力，并与其他早白垩世鸟类进行对比。结果显示，契氏鸟的扇状尾羽所产生的空气浮力小于同时代生活的今鸟型类，这有可能解释了反鸟类中具有空气动力学功能的尾羽形态普遍缺乏的现象。
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