Abstract: This paper reports new features of the dentition of Sinoconodon, an Early Jurassic mammal from the lower Lufeng Formation of Yunnan, China. Incisors and canines were replaced multiple times in Sinoconodon as in many non-mammalian cynodonts. New juvenile specimens of Sinoconodon have premolars which were replaced once before being permanently lost in the larger (thus older) specimens. Differentiation of premolars from molars and a single replacement of premolars are the derived features of modem mammals. The anterior molars (Ml— M2) were probably lost without replacement. The posterior molars (M3— MS) were replaced once. The skull experienced indeterminate growth while the teeth were being replaced in adult specimens. Sinoconodon is the sister taxon to all other mammals. The dental replacement of Sinoconodon could be interpreted as an intermediate stage in the character evolution from the primitive pattern of polyphyodont replacement seen in most cynodonts to the derived diphyodont replacement of mammals. From the polyphyodonty replacement and the substantial growth of the adult skulls of Sinoconodon, we infer that this taxon lacked the lactation and determinate growth typical of living mammals.

摘要： 中国云南下禄丰组的早侏罗世中国尖齿兽的新材料显示出从前未曾认识到的早期哺乳动物牙齿特征。中国尖齿兽的门齿和犬齿，像非哺乳类犬齿兽一样，是多次替换的。新的中国尖齿兽幼体标本保存有前臼齿，前臼齿替换一次之后，在较大(更老)的标本上就永久消失。犬后齿分化为前臼齿与臼齿，以及前臼齿仅替换一次是现代哺乳动物的衍生特征。中国尖齿兽前边的臼齿可能无后继齿替换而消失;后边的臼齿替换一次。中国尖齿兽当其成体的牙齿还在经受替换期间，头骨仍在继续生长。中国尖齿兽是所有其他哺乳动物的姊妹类群。中国尖齿兽的牙齿替换方式可解释为从爬