Sinoconodon rigneyi is an ancient mammaliamorph or early mammal (depending on systematic approach) that appears in the fossil record of China in the Sinemurian stage of the Early Jurassic period, about 193 million years ago. While in many traits very similar to non-mammlian synapsids, it possessed a special, secondarily evolved jaw joint between the dentary and the squamosal bones, which had replaced the primitive tetrapod one between the articular and quadrate bones, a trait commonly used to define mammals.