Evolution and Function of Dinosaur Teeth at Ultramicrostructural Level Revealed Using Synchrotron Transmission X-ray Microscopy

Chun-Chieh Wang, Yen-Fang Song, Sheng-Rong Song, Qiang Ji, Cheng-Cheng Chiang, Qingjin Meng, Haibing Li, Kiko Hsiao, Yi-Chia Lu, Bor-Yuan Shew, Timothy Huang, Robert R. Reisz
2015 Scientific Reports  
The relationship between tooth form and dietary preference is a crucial issue in vertebrate evolution. However, the mechanical properties of a tooth are influenced not only by its shape but also by its internal structure. Here, we use synchrotron transmission X-ray microscopy to examine the internal microstructures of multiple dinosaur teeth within a phylogenetic framework. We found that the internal microstructures of saurischian teeth are very different from advanced ornithischian teeth,
more » ... cting differences in dental developmental strategies. The three-tissue composition (enamelmantle dentin-bulk dentin) near the dentinoenamel junction (DEJ) in saurischian teeth represents the primitive condition of dinosaur teeth. Mantle dentin, greatly reduced or absent from DEJ in derived ornithischian teeth, is a key difference between Saurischia and Ornithischia. This may be related to the derived herbivorous feeding behavior of ornithischians, but interestingly, it is still retained in the herbivorous saurischian sauropods. The protective functions of mantle dentin with porous microstructures between enamel and bulk dentin inside typical saurischian teeth are also discussed using finite-element analysis method. Evolution of the dental modifications in ornithischian dinosaurs, with the absence of mantle dentin, may be related to changes in enamel characteristics with enamel spindles extending through the DEJ. To date, however, the internal fine structures of dinosaur teeth have not been thoroughly studied because of limitations in analytical techniques. For example, X-ray micro-computed tomography (μ -CT) can provide three-dimensional (3D) information on the internal microstructures of teeth non-destructively 14,15 , but cannot reveal internal structures at scales smaller than 1 μ m. When combined with focused ion beam (FIB) techniques, however, SEM-FIB can provide 3D internal information on specimens at a nanometer-level spatial resolution 16 , but these are destructive and time-consuming methods. In this study, we use synchrotron transmission X-ray microscopy (TXM) 17,18 to identify the 3D ultramicrostructures of various kinds of dinosaur teeth. TXM employs a Fresnel zone plate objective to achieve a spatial resolution of up to 30 nm 19 , along with ultrahigh-brightness synchrotron hard X-rays. This permits investigations into the diversity of 3D internal ultramicrostructures of dinosaur teeth from both saurischian and ornithischian dinosaurs and explore the evolutionary trends of these dinosaurs.
doi:10.1038/srep15202 pmid:26512629 pmcid:PMC4625602 fatcat:hccuyanuozcp3kciltp5hspwbe