Mixosaurid ichthyosaurs (mixosaurs) are a dominant group of Middle Triassic marine reptiles that was widely distributed in both Tethyan and Panthalassic terranes. They are represented by many excellently preserved specimens from all around the world and have been studied for more than one hundred years. Even so, their morphology is not adequately known. The systematics of mixosaurs is not well understood and their phylogeny has been controversial. The nomination of several Chinese mixosaurs makes the situation even worse. This thesis aims to provide a comprehensive review of Chinese mixosaurs and discuss their phylogenetic relationships. The detailed anatomy of only valid Chinese mixosaurid species Mixosaurus panxianensis is well established in this thesis. Its ontogenetic changes are also noted and a better diagnosis is given. A new morphotype of mixosaurs from a recently discovered fossil Lagerst?tte, the Luoping biota, is described in detail. This morphotype is similar to M. panxianensis but consistent differences are also present. The ecological comparison to M. panxianensis demonstrates that this morphotype represents a new taxon that is different from M. panxianensis. A nearly complete and articulated specimen of Phalarodon atavus from the Middle Triassic Luoping biota, Yunnan, South China is described. This is the first specimen of P. atavus discovered outside the Germanic Basin. The discovery of this specimen demonstrates a cosmopolitan distribution of P. atavus across the whole Tethyan ocean. The new specimen is also the first one preserving the postcranial anatomy of this species, providing the potential to evaluate its swimming ability for the first time. Functional morphology shows that this species is well adapted for a pursuit attack of prey, consistent with the distribution pattern of the species. Tooth crown morphology suggests that P. atavus may prefer externally soft prey such as belemnoids. Mixosaurs are divided into three ontogenetic stages based on the humeral morphology. The juvenile stage ...