鲨类作为有颌脊椎动物中的一个主要类群，在地史和现今的海洋环境中都扮演了保持生态平衡的关键角色。从泥盆纪兴起至今，鲨类已有四亿多年的演化历史。虽然大多数适应于海洋环境，但无论在地史中还是现今世界鲨类都是淡水生态系统中不可忽略的成员。本项申请以甘肃北山陆相三叠系中发现的淡水鲨类化石为研究材料，拟对掌握的弓鲨类和奇鲨类化石进行生物分类和分支系统学研究，并对弓鲨型和奇鲨型绝灭支系进行地理分布形式与分支演化关系的分析研究。本项研究所采用的多件化石标本除了常见的钙化软骨保存之外，还保存了稀有发现的软组织解剖结构的清晰印模，包括显示底栖习性的吻端触须、背棘基部肌肉、肝脏及消化道等内脏器官。此外，雄性个体保存有交配器官鳍脚的支撑软骨和软体印模。拟采用CT扫描成像手段揭示这些稀有保存的、约245百万年前远古鲨类的软体解剖特征。研究成果将可能投稿于PNAS/RSPB，Science Advances之类刊物。

Sharks are a successful group of jawed vertebrates, played and still playing an important role in the past and present in balancing marine ecosystems. Rising from Devonian time and still dominant in oceanic environments as fierce predators, sharks have a more than 420 Ma history. Most sharks are ocean dwellers but several extinct groups and some extant species independently evolved fresh-water adaptations. Although sharks in majority are marine, they played historically and still playing today a key role in fresh-water ecosystems of the world. The proposed research is based on fresh-water shark specimens collected from the Lower Triassic beds exposed in Beishan Hills, northern Gansu Province. Fossil material at hand includes specimens referable to Hybodontiformes, and more significantly, rare complete specimens of Xenacanthiformes. Hybodont specimens show exceptional preservation of soft anatomical structures, including clear impressions of nostril barbells, enlarged liver, alimentary tract, muscle at the base of dorsal spines, while male individuals also preserved paired claspers as copulatory organs with cartilage support. Such extremely valuable material provides us a rare opportunity to reveal and study the soft anatomy of an ancient shark of Triassic in age (~245 Ma). The proposed research will sample and CT-scan these specimens to reveal microstructures of these soft tissue and visceral organs. Research results in the form of short reports, if warranted, will be submitted to journals including PNAS/RSPB, or Nature Geoscience/Science Advances. Lengthy descriptive papers will be submitted to Journal of Vertebrate Paleontology, or Zoological Journal of the Linnean Society.