早期哺乳动物三尖齿兽类牙齿的超微结构

本文用扫描电镜研究了中国云南禄丰盆地下禄丰组发现的以及英国威尔士晚三迭世的三尖齿兽类牙齿的超微结构.其釉质具有准釉柱结构,它们呈并行排列从釉牙质界延伸到釉质外表面.这种准釉柱结构由很多羽支状排列的磷灰石微晶组成.微晶的C轴与准釉柱的长轴形成交叉的角度大约为10-20度.早期哺乳动物牙齿釉质的准釉柱结构,很可能是从爬行动物无釉柱结构向哺乳动物真釉柱结构进化过程中的标志.

ULTRASTRUCTURE OF TRICONODONT TEETH

The enamel ultrastructure studies of the fossil and extant mammalian teeth have furnishedinvaluable information for the clarification of evolutionary relationships, and in recent yearsgreat attention has been paid to the subject of studying the ultrastructure of the teeth of early mammals. There is general agreement that the enamel of all recent mammals is characterized by a prismatic structure. The prisms constitute the basic s?ructural units of such enamel. Moss (1969) believed that true prismatic enamel appeared only in the early Cretaceous Theria, and that the enamel of all earliest mammals, such as Morganucodon, was non-prismatic and continuous with a sawtoothed pattern of the apatite crystals, whereas Osborn and Hillman (1979) and Fosse et al. (1973) described prismatic enamel in non-therian multituberculates from Cretaceous, and Grine et al. (1979) found it in primitive mammal Eozostrodon (Morganucodon) from the Rhaeto-Liassic age. Recently, the enamel structure of certain late Triassic mammals: the Theria Symmetrodonta (Kuehneotheriidae), the Prototheria Multituberculata (Haramiyidae) and the Eotheria Triconodonta (Morganucodontidae) has been investiga?ed (Frank et al., 1984; Sigogneau-Russell et al., 1984; Frank et al., 1986) and these studies have reached the conclusion that the enamel in these early mammals possesses a s?ructural pattern defined as "preprismatic". In view of the differences between the results obtained by Grine et al. (1979) and by other authors mentioned above, concerning Triconodonta, it would be significant to study the enamel structure of the teeth in this group. Through courtesy of Professor Sun Ai-lin we were able to examine with SEM the structure of the teeth in some triconodont. In this instance we used for this study the following material: Morganucodon and Sinoconodon from lower Lufeng Formation, Yunnan Province, and Eozostrodon (Morganucodon) from Wales, England. The results are summarized below.