Tomoya Hanai & Takanobu Tsuihiji (2018)
Description of tooth ontogeny and replacement patterns in a juvenile Tarbosaurus bataar (Dinosauria: Theropoda) using CTâscan data.
The Anatomical Record (advance online publication)
Teeth are continually replaced in most of nonâmammalian gnathostomes to maintain their functional dentitions. To clarify the tooth replacement patterns in tyrannosaurid theropod dinosaurs, we examined wellâpreserved dentitions (both premaxillae, left maxilla, partial right maxilla, and both dentaries) of a juvenile Tarbosaurus bataar (MPCâD 107/7) using Xâray computed tomographic (CT) imaging. Threeâdimensional (3D) rendering of the dentitions and staging of replacement teeth allowed quantitative analyses of the tooth ontogeny and replacement patterns in this specimen. These strategies were validated by comparing the results between MPCâD 107/7 and extant crocodilians, which are taxa that have previously been studied using nonâCT methods. 3Dârendered dentitions of MPCâD 107/7 showed alternate replacement patterns between oddâ and evenânumbered alveoli. Such patterns were discontinuous at the premaxillaâmaxilla junctions, suggesting the division of replacement patterns between the two dentitions possessing morphoâfunctionally different features. The replacement process in the oddânumbered alveoli of the left maxilla sequentially proceeded from distal alveoli. Meanwhile, in the both dentaries, there were simple alternate patterns in which functional teeth would be simultaneously shed out in every second alveoli. Such a simple alternation had never been reported in the adult tyrannosaurid dentaries. Under this pattern, the half of functional teeth in a single dentition would be shed at the same time, which may hamper foraging functions. We conclude that the simple alternate patterns found in the dentary dentitions of MPCâD 107/7 represent transient condition in juvenile tyrannosaurids, suggesting ontogenetic changes in tooth replacement patterns in the tyrannosaurid dentary.