Description of Tooth Ontogeny and Replacement Patterns in a Juvenile Tarbosaurus bataar (Dinosauria: Theropoda) Using CT‐Scan Data

Abstract

Teeth are continually replaced in most of non‐mammalian gnathostomes to maintain their functional dentitions. To clarify the tooth replacement patterns in tyrannosaurid theropod dinosaurs, we examined well‐preserved dentitions (both premaxillae, left maxilla, partial right maxilla, and both dentaries) of a juvenile Tarbosaurus bataar (MPC‐D 107/7) using X‐ray computed tomographic (CT) imaging. Three‐dimensional (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 MPC‐D 107/7 and extant crocodilians, which are taxa that have previously been studied using non‐CT methods. 3D‐rendered dentitions of MPC‐D 107/7 showed alternate replacement patterns between odd‐ and even‐numbered alveoli. Such patterns were discontinuous at the premaxilla‐maxilla junctions, suggesting the division of replacement patterns between the two dentitions possessing morpho‐functionally different features. The replacement process in the odd‐numbered 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 MPC‐D 107/7 represent transient condition in juvenile tyrannosaurids, suggesting ontogenetic changes in tooth replacement patterns in the tyrannosaurid dentary. Anat Rec, 302:1210–1225, 2019. © 2018 Wiley Periodicals, Inc.

Sampling impacts the assessment of tooth growth and replacement rates in archosaurs: implications for paleontological studies

“…Investigating ontogenetic sampling effects on mean VEIW is hampered by the small sample size of this study, but the ontogenetic development of dental organization we find differs from previously reported patterns (Edmund, 1962;Erickson, 1992;Hanai & Tsuihiji, 2018). Erickson (1992) found a significant relationship between mean VEIW and body length in Alligator; however, we find no such strong evidence for ontogenetic sampling effects on mean VEIW.…”

“…Intradental data extrapolations are often based on one or multiple of the following assumptions: (1) mean VEIW is constant regardless of the developmental age of the tooth (i.e., does not vary significantly or consistently with distance from the pulp cavity); (2) the maximum number of von Ebner lines are preserved at any transect location (i.e., a transect taken anywhere on the tooth from pulp cavity to crown will capture all von Ebner lines reflecting the maximum age of the tooth); and (3) mean VEIW is consistent regardless of the transect position used for sampling (i.e., does not vary across the tooth). Assumption 1 forms the basis for using a subsection of a transect to derive a mean VEIW for a tooth ( Erickson, 1992 , 1996a , 1996b ; Gren, 2011 ; Gren & Lindgren, 2013 ; Erickson et al, 2017 ; Kear et al, 2017 ; Ricart et al, 2019 ; D’Emic et al, 2019 ), but contrasts with a competing hypothesis that teeth have different growth rates during their formation, which would result in wider VEIWs depending on distance from the pulp cavity (Y-H. Wu, 2018, personal communication, Lawson, Wake & Beck, 1971 ; Hanai & Tsuihiji, 2018 ; Finger, Thomson & Isberg, 2019 ), as well as with observations of flexible replacement rates coupled with metabolic activity (often seasonally influenced) in extant reptiles ( Cooper (1966) in Anguis fragilis , Delgado, Davit-Beal & Sire (2003) in Chalcides sexlineatus and Chalcides viridanus ) and mammals ( Klevezal, 1996 : 66f). Assumption 2 forms the basis for the use of transverse sections to derive tooth formation times ( Sereno et al, 2007 ; Gren, 2011 ; Gren & Lindgren, 2013 ; Kear et al, 2017 ; Ricart et al, 2019 ).…”

Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America1

“…4B, D). Comparison to other tyrannosaurids with in situ premaxillary teeth (Lambe 1917, Brochu 2003, Currie 2003a, Tsuihiji et al 2011, Hanai and Tsuihiji 2019 suggests that this is a feature of the first or second premaxillary teeth and that the curved carina is the mesial one. Therefore, this tooth likely represents the first or second right premaxillary tooth of a small individual.…”

Tooth Removal in the Leopard Gecko and the de novo Formation of Replacement Teeth

“…Polyphyodonty, or life-long tooth replacement, is a developmental process shared by most non-mammalian vertebrates. In polyphyodont reptiles, it has been well documented that replacement occurs in waves that pass from the back to the front of the mouth in alternating tooth positions ( Edmund, 1960 , 1962 ; Cooper, 1966 ; Kline and Cullum, 1984 ; Kline and Cullum, 1985 ; Fastnacht, 2008 ; Grieco and Richman, 2018 ; Hanai and Tsuihiji, 2019 ). One key component of the expression of these jaw-level replacement waves is that each tooth position cycles on a temporally delayed schedule from adjacent positions.…”