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： 生物学 >> 动物学 提交时间： 2017-11-07 合作期刊: 《古脊椎动物学报》
摘要： The transformation from a long reptilian tail to a shortened tail ending in a pygostyle and accompanied by aerodynamic fanning rectrices is one of the most remarkable adaptations of early avian evolution. However, no fossils directly capture this transition, and information regarding the structural morphology and the early evolution of the pygostyle in Mesozoic birds and their integuments is relatively limited. Here we provide a review of the pygostyle morphology of Early Cretaceous birds with comparison to the structure in living birds. This study emphasizes the convergent evolution of distally co-ossified caudal vertebrae in non-avian maniraptorans and early birds. There further exist distinct differences in pygostyle morphology between Sapeornithiformes, Confuciusornithiformes, Enantiornithes, and Ornithuromorpha. The morphology of the pygostyle and rectrices in early ornithuromorphs appear similar to that of extant birds, whereas the pygostyle in more primitive birds does not appear morphologically capable of supporting the rectricial bulbs and musculature necessary to control an aerodynamic fan-shaped tail. The rectricial bulbs and rectricial fan appear to have coevolved with the plough-shaped pygostyle early in the evolution of the Ornithuromorpha. This study also shows that the confuciusornithiform pygostyle was more similar to that of enantiornithines than previously recognized, consistent with the presence of nearly identical ornamental tail feathers in both groups.
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