蚤目的起源和演化过程是昆虫学家关注的一个重点。最近在我国发现的似蚤类化石表明跳蚤在侏罗纪中期已经出现，然而有关中生代跳蚤的类群、分类地位及其系统演化关系还存在较大争议。本课题基于我国东北白垩系地层发现的蚤类化石标本，对中生代蚤类做系统深入地研究：1. 调查中生代蚤类的种类多样性情况，建立可靠的蚤类化石的分类鉴定标准，澄清中生代蚤类的分类地位，寻找该时期蚤类多样性分化的原因和机制；2. 结合跳蚤的现生类群和新生代发现的材料，分析蚤类在演化过程中关键特征，特别是口器、外生殖器及栉状结构的变化规律；3. 统计中生代蚤类的伴生动物类型，探索其可能的寄主，分析各个地质时期伴生动物的差异，结合蚤类的形态特征变化规律，推断其与寄主的协同演化关系。

The origin and evolution of fleas have been key focal fields for entomologists and paleoentomologists. The new flea fossils from China indicate that basal fleas have appeared in the Middle Jurassic. However, there are still disputes about the diversity, taxonomic status, phylogenetic relationship and evolutionary trend of Mesozoic fleas. Based on the flea fossils from Cretaceous strata of northeastern China, this project will conduct a comprehensive and systematic study of the Mesozoic fleas, encompassing the following three key areas: 1. We will investigate the diversity of the Mesozoic fleas, create a credible classification system for fossil fleas, clarify the taxonomy of Mesozoic fleas, and explore the possible diversification mechanisms. 2. Combined with the extant fleas and the Cenozoic fossil fleas, we will analyze the trend of changes for key flea characters, especially the mouthparts, external genitalia and ctenidia on the tibia or body. 3. By statistically analyzing the contemporaneous vertebrates, we will deduce potential hosts of the Mesozoic fleas. Furthermore, we will infer the co-evolution relationships between fleas and their hosts by comparing the different groups of potential host vertebrates in various geological periods, and matching them with the trend of changes for key morphological characters of fleas.