Abstract: A new genus and species of a basal ornithurine bird is reported from the Lower Cretaceous Jiufotang Formation of Jianchang, Liaoning, China. It is represented by a nearly complete articulated skeleton of a sub-adult individual. It is distinguishable from other known ornithurines by possessing a combination of features including at least 16 small and conical teeth on the dentary, scapula strongly curved, metacarpal I robust and wider than other metacarpals, first manual digit long and extending beyond distal metacarpal II, and length ratio of humerus+ulna+metacarpal II to femur+tibiotarsus+tarsometatarsus is approximately 1.1. Phylogenetic analysis indicates that the the new taxon is a basal ornithurine.Jianchangornis represents the second Early Cretaceous bird with the preservation of a predentary bone, which may further confirm that a predentary could be a feature common to Mesozoic ornithurines. The advanced features of the pectoral girdle, sternum and wings of the new bird indicate its powerful flight capability, and the hindlimb bone and toe proportions as well as the ungual morphology suggest a terrestrial locomotion similar to those of Yanornis and Yixianornis. The associated fish fragments may indicate a piscivorous diet consistent with the dentation of the new bird. The discovery of a new basal ornithurine further shows that the diversification of the Ornithurae is probably no less than the enantiornithes, and the near lakeshore adaptation had definitely played a key role in the early ornithurine radiation.

摘要： 依据一近完整的相关节的骨骼化石，记述了辽宁建昌早白垩世九佛堂组原始今鸟类一新属种：小齿建昌鸟(Jianchangornis microdonta gen. et sp. nov.)。新鸟个体较大，但从骨化程度分析，正型标本可能属于一亚成年个体。具有一些进步特征，如胸骨及龙骨突加长，乌喙骨具有发育的前乌喙突以及和肩胛骨关联的关节窝，叉骨“U”字型，愈合荐椎包括9？10枚荐椎，尾综骨短小，第二、三掌骨远端愈合，跗跖骨完全愈合等，表明新属无疑属于今鸟类。在以下特征组合上很容易和已知的早白垩世今鸟类化石相区别：齿骨上至少有16枚细小牙齿，从齿骨前端向后沿齿骨大部密集排列；肩胛骨强烈弯曲；第一掌骨粗壮，较其他掌骨宽；第一指长并且远端延伸明显超过第二掌骨；肱骨＋尺骨＋第二掌骨与股骨＋胫跗骨＋跗跖骨的长度比例约为1.1。系统发育分析表明新属属于基干的今鸟类。新发现的材料第二、三掌骨远端愈合很好，但近端却未完全愈合，这一特征尚未见于其他已知鸟类，或许表明今鸟类腕掌骨的愈合和现生鸟类的跗跖骨一样是从远端开始的，不同于反鸟类和其他基干鸟类。建昌鸟的下颌还保存了一个前齿骨，这是继早白垩世红山鸟之后的另一例报道，可能进一步表明这一结构在今鸟类中曾普遍出现。新鸟肩带、胸骨和前肢的特征显示了和现代鸟类相近的飞行能力，其后肢、脚趾的比例以及趾爪的形态等显示和燕鸟、义县鸟等相似的地栖特征。保存于标本上的鱼类残骸可能显示了建昌鸟食鱼类的习性。今鸟类新属种的发现进一步表明，早白垩世这一进步鸟类类群的分化已不亚于反鸟类，湖滨环境在今鸟类的早期演化中确实扮演了重要的角色。