Kalthoff Daniela C
Department of Paleozoology, Swedish Museum of Natural History, Stockholm SE-104 05, Sweden.
J Morphol. 2011 Jun;272(6):641-61. doi: 10.1002/jmor.10937. Epub 2011 Mar 31.
A striking difference between xenarthrans and other mammals is the complete loss of tooth enamel in all members but the earliest armadillos. However, sloth and armadillo teeth show structured wear facets, which in all other mammals are formed by tooth enamel. How is that possible? Here, I report about an analysis of fossil and recent xenarthran dental hard tissue microstructure. It shows that osteodentine is not exclusive to fossil Cingulata, but also occurs in some recent taxa. Furthermore, I found profound modifications of orthodentine architecture in comparison to other mammals. Remarkable features are (a) a larger proportion of the highly mineralized, collagen-free peritubular dentine, and (b) a modified architecture of the odontoblastic process with frequent interconnections between the extensions and unusually intensive branching of the extensions forming a complex meshwork, penetrating the intertubular dentine matrix. The orthodentine microstructural build-up is unique in Folivora and Cingulata.
异关节类动物与其他哺乳动物之间的一个显著差异是，除了最早的犰狳外，所有成员的牙釉质都完全缺失。然而，树懒和犰狳的牙齿显示出有结构的磨损面，而在所有其他哺乳动物中，这种磨损面是由牙釉质形成的。这怎么可能呢？在此，我报告一项对化石和现代异关节类动物牙齿硬组织微观结构的分析。分析表明，骨齿质并非化石贫齿目独有的，在一些现代类群中也存在。此外，与其他哺乳动物相比，我发现正齿质结构有深刻的改变。显著特征包括：（a）高度矿化、无胶原蛋白的管周牙本质比例更大；（b）成牙本质细胞突起的结构发生改变，其延伸部分之间频繁相互连接，且延伸部分异常密集分支，形成一个复杂的网络，穿透管间牙本质基质。正齿质的微观结构在树懒亚目和贫齿目中是独特的。
