3月18日,，《自然》Nature雜志在線發(fā)表了中科院古脊椎動物與古人類研究所周忠和院士及其團隊成員與山東臨沂大學鄭曉廷,、王孝理、王巖,，以及南非比勒陀利亞大學Fritz Huchzermeyer合作完成的一項研究成果——“早白堊世鳥類卵泡的精美保存對研究恐龍繁殖行為的意義”（Exceptional preservation of ovarian follicles in Early Cretaceous birds hints at dinosaurian reproductive behaviour）,。
該研究基于山東天宇自然博物館保存的三件早期鳥類化石（一件為長尾的熱河鳥，另外兩件為未命名的反鳥類）,，對它們罕見保存的卵巢中的濾泡化石進行了研究,。如此精美的鳥類軟組織繁殖器官保存以前尚未見報道。該研究表明,，盡管與鳥類關系最近的恐龍與鱷魚一樣,，還使用兩個卵巢和兩條輸卵管，但早期鳥類顯然已經(jīng)只保留一個有效的卵巢和一條輸卵管（身體左側）,。他們據(jù)此推測,，身體右測卵巢和輸卵管的功能退失可能發(fā)生在恐龍向鳥類過渡的階段，很可能與適應飛行需要的體重減少有關,。
他們的研究還表明,，盡管早期鳥類已經(jīng)具有了一些現(xiàn)代鳥類的繁殖特征，但在卵泡的數(shù)量,、卵泡大小的差異等方面還顯示了原始的特征,，表明了相對于現(xiàn)代鳥類較低的新陳代謝水平,。在系統(tǒng)演化上，熱河鳥代表了最原始的鳥類之一,，而反鳥類代表了最基干的鳥類與進步鳥類之間的過渡類型,。該研究也顯示，熱河鳥的繁殖行為相對更加原始,，而反鳥類的繁殖行為較為進步,，它們代表了爬行類與現(xiàn)生鳥類之間繁殖行為的不同演化過渡階段。
該研究的另外一個結論是：與爬行類和恐龍相似,，早期鳥類的性成熟早于身體（骨骼）的成熟,，這不同于現(xiàn)生鳥類。此外,，鳥類卵巢濾泡化石的發(fā)現(xiàn)還提供了該類標本確切的性別證據(jù),，將有助于進一步研究早期鳥類的性雙型等科學問題。
該項研究得到了科技部973項目以及國家自然科學基金等項目的支持,。（生物谷Bioon.com）
doi:10.1038/nature11985
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Preservation of ovarian follicles reveals early evolution of avian reproductive behaviour
Xiaoting Zheng, Jingmai O’Connor, Fritz Huchzermeyer, Xiaoli Wang, Yan Wang, Min Wang & Zhonghe Zhou
The two groups of archosaurs, crocodilians and birds, form an extant phylogenetic bracket for understanding the reproductive behaviour of dinosaurs. This behaviour is inferred from preserved nests and eggs, and even gravid individuals1. Data indicate that many ‘avian’ traits were already present in Paraves—the clade that includes birds and their close relatives—and that the early evolution of the modern avian form of reproduction was already well on its way2, 3. Like living neornithine birds, non-avian maniraptorans had daily oviposition and asymmetrical eggs with complex shell microstructure, and were known to protect their clutches4, 5, 6. However, like crocodilians, non-avian maniraptorans had two active oviducts (one present in living birds), relatively smaller eggs, and may not have turned their eggs in the way that living birds do1, 6. Here we report on the first discovery of fossilized mature or nearly mature ovarian follicles, revealing a previously undocumented stage in dinosaur reproduction: reproductively active females near ovulation. Preserved in a specimen of the long bony-tailed Jeholornis and two enantiornithine birds from the Early Cretaceous period lacustrine Jehol Biota in northeastern China, these discoveries indicate that basal birds only had one functional ovary, but retained primitive morphologies as a result of their lower metabolic rate relative to living birds. They also indicate that basal birds reached sexual maturity before skeletal maturity, as in crocodiles and paravian dinosaurs. Differences in follicular morphology between Jeholornis and the enantiornithines are interpreted as forming an evolutionary gradient from the reproductive condition in paravian dinosaurs towards neornithine birds. Furthermore, differences between the two enantiornithines indicate that this lineage might also have evolved advanced reproductive traits in parallel to the neornithine lineage.
