Abstract: Peltopleuriformes are a stem group of neopterygian fishes from the Middle–Late Triassic marine ecosystems in Europe and South China, including the Peltopleuridae and Thoracopteridae. Among them, peltopleurids are commonly small-sized fishes with a standard length (SL) rarely exceeding 55 mm. Here, a new peltopleurid, Peltopleurus tyrannos sp. nov., is described based on three well-preserved specimens from the Middle Triassic (Ladinian) of Fuyuan, Yunnan and Xingyi, Guizhou, China. The discovery documents the largest species (SL = 72 mm) of this genus in the Middle Triassic and provides new insights into the morphologic and trophic diversifications of peltopleurids. In addition to large conical teeth on the oral margins of the jaws, the newpeltopleurid bears many blunt teeth of various sizes on the oral margin of the palatopterygoid, which may be used for crushing some hard-shelled invertebrates (e.g., crustaceans) or small armored fishes. By contrast, the more commonly founded relative, P. orientalis, from the same ecosystem (Xingyi Biota) is toothless and has a much smaller body size (SL=26 mm), and probably represents a schooling fish that fed on small planktonic invertebrates. The new finding shows that Peltopleurus from the late Middle Triassic Xingyi Biota of South China had evolved into two different ecomorphotypes.