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

Abstract

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, reflecting differences in dental developmental strategies. The three-tissue composition (enamel–mantle 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.

The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends

“…tion. On the other hand, crown ornamentations (CI of 0.49) and microstructure (CI of 0.62), although bearing functional properties and linked to diet (e.g., Sander, 1999;Brink et al, 2015Brink et al, , 2016Wang et al, 2015), are the least homoplastic possibly because they require more complex developmental/genetic mechanisms to evolve than other dental features under the same evolutionary pressure. Indeed, crown microstructure has been suggested to bear some phylogenetic potential in dinosaurs (Hwang, 2005(Hwang, , 2010Wang et al, 2015).…”

Ultramicrostructural reductions in teeth: implications for dietary transition from non-avian dinosaurs to birds

“…The adaptive changes in internal tooth structure related to a shift in feeding ecology during this critical transition are not fully understood, despite a few studies focusing on non-avian dinosaurs that are distantly related to avialans [4,12]. Here we report the ultramicrostructural details in enantiornithines, ornithuromorphs, non-ornithothoracine avialans, and non-avian paravian theropods (microraptorines and troodontid dinosaurs) using both scanning electron microscopy (SEM) and synchrotron transmission X-ray microscopy (TXM) [13]. We found similar tooth microstructure between one Microraptor species and other Early Cretaceous birds.…”

“…We found similar tooth microstructure between one Microraptor species and other Early Cretaceous birds. The lack of mantle dentin with interglobular porous spaces (IGS) between the enamel and orthodentin [13,14] in avialans indicates a derived condition in Saurischian dinosaurs. In addition, the internal ultramicrostructure of teeth provides further evidence for divergent feeding ecology or food acquisition and processing in birds and closely related paravians.…”

A comparative study of the mechanical properties of a dinosaur and crocodile fossil teeth

“…Experiments performed on bovine teeth showed that crack arresting occurs in DEJ only when the crack initiation takes place in enamel region [44]. Other studies [45] discussed the importance of the region between DEJ and dentin, the inter-globular porous space (IGS), in crack deflection and energy absorption during crack propagation [44].…”