The Mechanism of Trace-element Accumulation into Tooth Enameloid/Enamel and Its Evolutionary Changes.

在过去的研究中，人们认为铁或其他微量元素在鱼类类釉质中的积累可能与鱼类的摄食习性有关。然而，目前的调查结果并没有为这些先前的概念提供支持的证据。目前的研究表明，软骨鱼和硬骨鱼的类釉质矿物相最充分地表征为氟化碳酸盐磷灰石。然而，磷灰石晶格的氟化、铁积累和碳酸化程度在不同物种之间有所不同，在同一物种内，处于不同的发育阶段。值得注意的是，观察到的氟化物和铁的积累可能反映了古代体液的组成或矿化环境。综上所述，铁和氟化物在鱼类类釉中积累是在放线鱼谱系中实现的。根据所获得的证据，F在牙釉质中积累的起源可追溯到放线鸟进化的枝生阶段，而高氟化物浓度的起源可追溯到新鸟进化阶段。最有可能的是，铁积累机制在F积累之前已经进化，可能与腕肢动物或相关物种一起出现。事实上，除了鲨鱼之外，没有一种硬骨鱼类表现出高铁和低铁的组合。因此，铁和铁的积累机制可能是在不同的进化背景下独立发展起来的，其积累机制可能隐藏在从鱼类到两栖动物到哺乳动物的进化过程中。从目前的研究结果来看，在棘纲到四齿纲的进化过程中，最有可能的是铁积累在发育的类釉质中丢失了，这是基于在四齿纲和棘纲的类釉质中铁含量的明显对比。

In the past studies, it was postulated that accumulation of iron or other trace elements in fish enameloid should be related to feeding habits of the fishes. However, the results of the present investigation yielded no supportive evidence for those previous concept. The present studies indicate that the mineral phase of enameloid in both cartilagineous and bony fishes is most adequately characterized as fluoridated carbonatoapatites. However, the degree of fluoridation, Fe accumulation, and carbonation of the apatite lattice vary among the species and, within a species, at different developmental stages. It is of interest to consider that the observed accumulation of fluoride and iron may reflect the composition of ancient body fluid or in the mineralizing milieu. The overall results suggest that the accumulation of iron and fluoride into fish enameloid realized in the Actinopterygian lineage. In light of the evidence obtained, the origin of the F accumulation into tooth enameloid can be traced back to the cladistian stage of Actinoperygian evolution, while that of high fluoride concentration to the Neopterygian stage. Most likely, the iron accumulation mechanism has been evolved prior to the F accumulation, probably emerging with the brachiopterygian or relevant species. Indeed, there are no teleostean fishes which exhibits a combination of high F and low Fe, except for sharks. Thus it seems likely that the mechanisms of F and Fe accumulation have been developed independently with different evolutionary backgrounds and that its accumulation mechanisms have been buried in the evolutionary process from fishes through amphibian to mammals. At present, it is most likely that iron accumulation into developing enameloid has been lost during the evolution from the Acanthuridae to the Tetraodontoidei, based on the finding that a shatp contrast with respect to the iron content was obtained between the enameloid of the Tetraodontoidei and Acanthuridae.