Department of Biological Sciences, University of Cape Town, Private Bag X3, Cape Town 7700, South Africa.
Nat Commun. 2013;4:1381. doi: 10.1038/ncomms2377.
Hundreds of specimens of the beaked bird Confuciusornis sanctus have been recovered from Early Cretaceous lake deposits of northeastern China. These birds show remarkable variation in size and plumage, with some displaying two long, central ornamental rectrices (tail feathers) and others lacking them altogether. Although, traditionally specimens with ornamental rectrices were interpreted as males and those without them as females, this supposed sexual dimorphism has remained unconfirmed. Here we report on the discovery of medullary bone, a tissue unique to reproductively active female birds, in a specimen of C. sanctus (DNHM-D1874) lacking these feathers. Our discovery constitutes the first case of gender identification in a Mesozoic bird, and it provides undisputed evidence that individuals of C. sanctus without ornamental rectrices are females. By permitting gender identification in C. sanctus, our results provide insight into the onset of sexual maturity and attainment of adult body size of this and other early birds.
数百件孔子鸟的标本已从中国东北早白垩世湖相沉积物中采集到。这些鸟类在大小和羽毛方面表现出显著的变化，有些显示出两条长长的中央装饰性尾羽，而另一些则完全没有。尽管传统上，带有装饰性尾羽的标本被解释为雄性，而没有这些尾羽的标本被解释为雌性，但这种所谓的性别二态性尚未得到证实。在这里，我们报告了在一个缺乏这些羽毛的孔子鸟（DNHM-D1874）标本中发现了髓质骨，这是一种只存在于有繁殖能力的雌性鸟类中的组织。我们的发现构成了中生代鸟类中首次进行性别鉴定的案例，并且提供了无可争议的证据，证明没有装饰性尾羽的孔子鸟个体是雌性。通过允许对孔子鸟进行性别鉴定，我们的结果为了解这种鸟类和其他早期鸟类的性成熟开始和成年体型的获得提供了线索。
