叶肢介是一种淡水甲壳类动物,个体一般在几毫米到两厘米之间。它的英文名叫clam shrimp,因为它的软体像虾,具有很多附肢,外裹一对几丁质壳瓣,形似蚌壳。叶肢介从泥盆纪开始出现,中生代时其演化中心从欧洲迁移到了东亚,侏罗纪和白垩纪时它们的分异和演化达到顶峰,新生代则进入衰亡阶段。叶肢介化石一般出现在陆相地层中,由于它数量多、演化快、分布广泛,近年来已成为中国和邻近地区中生代非海相生物地层划分和对比研究的重要手段之一。中国大陆侏罗系和白垩系主要是陆相沉积,按古地理和生物地理区系,早、中侏罗世我国南北具有统一的叶肢介动物地理区系,如早侏罗世早期的白田坝古渔乡叶肢介动物群,早侏罗世晚期的东方似渔乡叶肢介动物群;中侏罗世早期的自流井真叶肢介动物群;从中侏罗世晚期开始南北开始分异,在南方西南湖群发育了古狭叶肢介群,在北方发育了中国瘤叶肢介群;到晚侏罗世南方西南湖群 Leaf extremity is a freshwater crustacean, individuals generally in a few millimeters to two centimeters. Its English name is clam shrimp, because of its software like shrimp, with many appendages, wrapped in a pair of chitin shell, shaped like a clam shell. Leaf veins began to appear from the Devonian. During the Mesozoic Eocene, their evolution centers migrated from Europe to East Asia, Jurassic and Cretaceous. Their differentiation and evolution reached the peak, while Cenozoic entered the stage of decline. Because of its large number, rapid evolution and wide distribution, leaf-exoduomet fossils usually appear in terrestrial strata. In recent years, foliar mesotrons have become one of the important means to divide and contrast the Mesozoic non-marine biostratigraphy in China and its adjacent areas. Jurassic and Cretaceous in mainland China are mainly continental facies. According to palaeogeography and biogeographical system, the Early and Middle Jurassic have a unified geographical region of leaf-exoduomes in North and South of China. For example, in the early Jurassic, Yebaoguanzoic fauna in the dam ancient fishing village, the Lateral Jurassic Late Silurian herbivore community in the East; the middle Jurassic artesian leaf basaltic animals in the early stage; from the late Middle Jurassic, , In the southwestern Southwest Lake Group ancient Palaeaura group developed in the north of Chinese tumor leaf melatonin group; to the late Jurassic southwestern Southwest Lake Group