未成熟羽毛在早白垩世热河鸟类生物群幼年反鸟类中的首次报道

doi:10.19615/j.cnki.1000-3118.190823

摘要/Abstract

摘要：

换羽——将一种羽毛替换成另一种的过程——对鸟类具有非常重要的生物学作用。这一过程能够每年将受损的羽毛替换掉,产生与个体发育相关的羽毛类型,或产生处在繁殖活跃期成年个体所具有的覆羽类型。处于萌发阶段的未成熟羽毛被角质鞘包裹,外形呈狭窄管状,没有明显特征。角质鞘完全脱落标志着羽毛的成熟。虽然热河生物群发现了大量与皮肤衍生物相关的化石,但是确切无疑的未成熟羽毛还未有报道,尽管九佛堂组(120 Ma)发现的一件窃蛋龙类——似尾羽龙,保存了疑似未成熟的羽毛。一件缅甸琥珀(9 Ma)中的反鸟幼崽保存了处于萌发阶段的羽毛,由于是三维保存,对外皮结构的解读更为直观。描述了发现于九佛堂组的4件反鸟类幼年个体上保存的疑似未成熟羽毛。与现生鸟类相似,上述疑似未成熟羽毛的近端窄,外形没有明显结构,仅在末端显示出分叉的羽支。认为此前报道的反鸟类多齿胫羽鸟(Cruralispennia multidonta)掌部和胫跗骨上的相似类型的羽毛可能也是未成熟羽毛。未成熟羽毛和与性双型相关的装饰性羽毛在反鸟类幼年个体上的同时出现,可能说明新鸟类具有的复杂的换羽模式——与性双型相关的装饰性羽毛在个体达到性成熟若干年后(经历了若干次换羽后)才会出现,并且只在更接近鸟类冠群的一些类群中出现。

关键词: 中生代, 热河生物群, 鸟类, 鞘羽, 羽毛, 换羽

Abstract:

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.

Key words: Mesozoic, Jehol Biota, Aves, pin feather, plumage, molt

中图分类号:

Q915.865

邹晶梅, 福雅曼, 王敏, 郑晓廷. 未成熟羽毛在早白垩世热河鸟类生物群幼年反鸟类中的首次报道. 古脊椎动物学报, 2020, 58(1): 24-44.

Jingmai K. O’CONNOR, Amanda FALK, WANG Min, ZHENG Xiao-Ting. First report of immature feathers in juvenile enantiornithines from the Early Cretaceous Jehol avifauna. Vertebrata Palasiatica, 2020, 58(1): 24-44.

图/表 8

Fig. 1 Immature feathers in juvenile neornithines A. late immature remiges in Pelecanus occidentalis LACM 86193; B. mid to late immature remiges in Otus asio LACM 100682; C. mid to late immature remiges in Turdus migratorius LACM 100338; D-F. mid immature contour feathers in Tyto alba LACM 100815 (nestling). Note tubular (‘ribbon-like’ in compression fossils) appearance of the proximally sheathed portions of the developing feathersAbbreviations: fv. feather vane (exposed distal to the proximal developing portion of the feather still encased in the waxy sheath); sh. waxy sheath. Scale bars = 1 cm

Fig. 2 Illustration of the stages in feather development A. pin feather, early immature stage; B. blood-quill, mid-immature stage; C. late immature stage; D. mature feather

Fig. 3 Unusual tail feathers in juvenile Similicaudipteryx STM 4-1, line drawing of rectrices (modified from S. Abramowicz, O’Connor et al., 2012)Abbreviations: er. exposed rachis; other abbreviations see Fig. 1. Scale bar = 1 cm

Fig. 4 Juvenile enantiornithine IVPP V 14980 preserving probable immature feathers A. slab A; B. slab B; C. close up of boxed area marked in A showing details of the immature feathers along the distal ulna and proximal carpometacarpus; D. slab B under laser-stimulated fluorescence; E. boxed region in D enlarged to show details of the immature feathers under normal lightAbbreviations: if. immature feathers; other abbreviations see Fig. 1. Scale bars = 1 cm

Fig. 5 Juvenile enantiornithine IVPP V 15564 preserving probable immature feathers A. slab A; B. left forelimb (enlarged from boxed region indicated in A);C. boxed region in B enlarged to show detail of the immature feathers on the proximal humerus;D. possible late stage developing tail feathers (boxed region indicated in A) under laser-stimulated fluorescenceAbbreviations: rm. remige; other abbreviations see Figs. 1, 4. Scale bar = 1 cm

Fig. 6 Juvenile enantiornithines preserving possible immature feathers A. STM 34-1 with mature remiges and densely preserved body feathers that appear to be immature; B. STM 34-9 with sparsely preserved probable immature body feathers and a pair of rachis-dominated feathers; C. close up of the area marked in B showing early and mid-immature stage feathers on the forelimb. Scale bars = 1 cm

Fig. 7 Unusual feathers in Cruralispennia IVPP V 21711 A. photograph of the full slab; B. close up of the unusual feathers on the tibiotarsusScale bar in A equals 1 cm; scale bar in B equals 5 mm. Abbreviations see Fig. 4

Table 1 List of neonate and juvenile enantiornithines preserving plumage

Specimen No.	Feathers	Remiges	RDFs	body coverts	mature feathers	immature feathers	No. Sternal ossifications
IVPP V 14980	×					body feathers (wing)	4?
IVPP V 15564¹⁾	×					remix, body feathers (wing), RDFs?	3
IVPP V 14287²⁾	×					remiges, body feathers	0
STM 34-1¹⁾	×	×		×	remiges	body feathers (neck, wing, abdomen, legs)	4
STM 34-9¹⁾	×		×	×		wing/neck/abdomen body feathers, RDFs?	4
STM 34-2¹⁾	×	×		×	remiges, body feathers		3
STM 34-7¹⁾	×	×	×	×	remiges, body feathers, RDFs (pair)		4
GMV-2158³⁾	×	×?	-	×?	possible remiges	possible body feathers	3
GMV-2159³⁾	×	×	×?	?	remiges, possible tail and body feathers	none (visibly preserved)	4
GMV-2156/NIGP-130723⁴⁾	×	×		?	remiges, possible body feathers	none (visibly preserved)	3
HPG-15-1⁵⁾					remiges, body feathers (primitive)	rectrices (RDFs)	?
UFRJ-DG 031 Av⁶⁾	×		×	×	rectrices, body feathers		?
MPCM-LH-26189⁷⁾	×	×		×	remiges, body feathers		3

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