Abstract: We conduct histological analysis of two sexually mature fossil birds from the Lower Cretaceous Jehol Group referable to Jeholornis sp. and Enantiornithes indet. Histology confirms that in these lineages of basal birds, sexual maturity was achieved before skeletal maturity. The samples reveal structural differences from previously described relevant specimens, indicating that the ontogenetic changes in bone tissue that occur in Mesozoic birds are more complicated than previously recognized. The female specimen ofJeholornis sectioned here is more vascularized than previously described specimens, with both reticular and longitudinal canals. The enantiornithine bone tissue is most similar to that reported for the Early Cretaceous Concornis, primarily formed by parallel-fibered bone but more vascularized than other reported adult enantiornithine specimens. The bone shows a distinct decrease in the rate of bone deposition, inferred to represent the onset of sexual maturity.

摘要： 对发现于早白垩世热河生物群的两个达到性成熟的热河鸟(Jeholornis sp.)和反鸟(Enantiornithes indet.)的雌性个体进行了骨组织学研究。结果表明，在热河鸟和反鸟中，个体达到性成熟的时间要早于骨骼成熟。新的骨组织切片显示出与以往报道不同的骨组织结构，表明中生代鸟类的骨组织结构在个体发育过程中的变化比原有的认识更为复杂。与以前报道过的热河鸟的骨组织结构相比，本文研究的雌性热河鸟的骨骼切片显示出更高的血管化程度，网状和径向的管道同时存在。反鸟的骨组织结构与此前报道过的早白垩世的反鸟Concornis相似，其骨壁主要是由平行纤维板骨组成，骨骼的血管化程度要高于以往报道过的反鸟成年个体。骨组织结构显示出该反鸟个体的骨质沉积速率已明显下降，表明其已经达到了性成熟阶段。