作者：吴  倩，邹晶梅，李志恒，艾莉达

摘要：飞行的早期演化是古生物研究的热点问题之一。现生鸟类演化出多种不同飞行方式，然而对中生代鸟类飞行方式的研究亟需寻找具有指示意义的指标。骨骼与关节组织是尤其是乌喙骨-叉骨关节是实现鸟类飞行功能的重要组成，因此其关节的组织形态可能有助于反映现生鸟类的飞行方式。鸟类膜质骨中的次级软骨受到表观遗传的重要影响，只能在关节受到肌肉运动刺激的情况下形成，因此能够反映鸟类关节的形成力学环境；在对三种不同飞行方式的现生鸟类(珠颈斑鸠、树麻雀和普通楼燕)，以及热河生物群中最为常见的古鸟类之一孔子鸟(Confuciusornis)的叉骨乌喙骨关节的组织学特征进行分析，显示在所有三种现生鸟类中，叉骨与乌喙骨之间均存在可动关节，并且在叉骨上存在次级软骨。而孔子鸟的叉骨上也存在次级软骨，这是次级软骨组织在中生代鸟类叉骨化石中的首次报道。进一步分析不同现生鸟类物种的次级软骨组织形态的差异，很可能潜在指示了飞行方式所造成的关节形态差异。
关键词: 飞行演化，鸟类，孔子鸟，叉骨，组织学，次级软骨

Cartilage on the furculae of living birds and the extinct bird Confuciusornis: a preliminary analysis and implications for flight style inferences in Mesozoic birds？
WU Qian，Jingmai O’CONNOR，LI Zhi-Heng，Alida M. BAILLEUL

Abstract   The early evolution of flight is one of the most studied topics in vertebrate paleontology. Living birds have evolved to utilize a variety of flight styles, but studies focused on inferring flight strategies in Mesozoic birds are often contradictory and without a clear consensus, making it necessary to find additional informative characteristics that can be useful for inferences in fossils. Virtually nothing is known about the histology of the avian pectoral girdle, even though skeletal and joint tissues are key candidates to solve form-function relationships. Avian secondary cartilage found on the dermal bones of the avian skeleton is influenced by epigenetics and only forms when joints are stimulated by muscle contractions. As the only dermal bone in the avian postcranium, the furcula is a potential site for the formation of furcular secondary cartilage and merits further attention. It is still unknown whether living and fossil birds have furcular secondary cartilage. Here we present histological analyses conducted on the furcula-coracoid articulation in three living birds (Spilopelia chinensis, the Spotted dove; Passer montanus, the Eurasian tree sparrow; and Apus apus, the Common swift), taxa that utilize different flight styles, and one of the most common fossil birds of the Jehol Biota, Confuciusornis. Secondary cartilage was identified on the furculae of the living birds and of Confuciusornis, representing the first report of furcular secondary cartilage in the fossil record. Clear differences in secondary cartilage morphologies were observed in the living species, but additional data is required to establish a strong form-function relationship that could be useful for making inferences in Mesozoic birds.
Key words   Evolution of flight, birds, Confuciusornis, furcula, histology, secondary cartilage