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

Abstract

Vertebrate teeth are complex structures adapted in terms of shape and structure to serve a variety of functions like biting and grinding. Thus, examining the morphology, composition and mechanical properties of the teeth can aid in providing insights into the feeding behaviour of extinct species. We here provide the first mechanical characterisation of teeth in a spinosaurid dinosaur, Suchomimus tenerensis, and a pholidosaurid crocodylomorph, Sarcosuchus imperator. Our results show that both species have similar macrostructure of enamel, dental and interfacial layers, and similar composition, the main constituent being fluoroapatite. Microindentation tests show that Suchomimus teeth have lower elastic modulus and hardness, as compared to Sarchosuchus. On the contrary, Sarcosuchus teeth have lower toughness. Nanoindentation showed the existence of mechanical gradients from dentin to enamel in Suchomimus and, less prominently, in Sarcosuchus. This was also supported by wear tests showing that in Suchomimus the dentin region is more wear-prone than the enamel region. With still scarce information available on the dietary regimes in extinct species the analysis of micro and nano-mechanical properties of fossils teeth might be a help in targeting specific biological questions. However, much is still unknown concerning the changes underwent by organic material during diagenesis making at present impossible to definitely conclude if the differences in the mechanical properties of Suchomimus and Sarchosuchus here retrieved imply that the two species adopted different strategies when dealing with food processing or are the result of disparate taphonomic histories.

Nanomechanical variability in the early evolution of vertebrate dentition

“…The values of E recovered from D. obliquicostatus fall within the range of other vertebrate phosphatic feeding elements (teeth) on both the low value and high value ends of the scale (Table 1 ) 17 , 18 , 20 , 36 – 38 . Given that lamellar crown tissue of conodonts is analogous to the more derived tooth materials of later vertebrates (enameloid, enamel) 1 , 3 , 5 , 8 , the similarity in the maximum values of this critical material property are striking.…”

“…The few studies conducted demonstrate that there are clearly variations in E across the functional surface (buccal to lingual) and along the apical-cervical axis in bovine dentine 19 and human molars 20 . Similar stiffness mapping of enamel and dentine in dinosaur and crocodylomorph teeth shows considerable variability of appoximately 25% of the maximum values of E for each material 18 . The range of E appears to be smaller (25%-30%) across the functional surface of vertebrate teeth compared to longitudinal variations from the functional surface to the enamel-dentine junction, which can exceed 50% 18 , 20 .…”

“…Similar stiffness mapping of enamel and dentine in dinosaur and crocodylomorph teeth shows considerable variability of appoximately 25% of the maximum values of E for each material 18 . The range of E appears to be smaller (25%-30%) across the functional surface of vertebrate teeth compared to longitudinal variations from the functional surface to the enamel-dentine junction, which can exceed 50% 18 , 20 . Conodont bioapatite is composed of distinct tissue types, each composed of varying amounts and arrangements of hydroxyapatite nanocrystallites in an organic matrix 8 .…”

Crocodile Tooth Histology from a Pliocene Deposit in Chinchilla, Queensland

“…Both modern and fossil crocodylian tooth structure and function have been studied, including experimental bio mechanics of biting force, tooth replacement questions, and dentine incremental lines in alligatorids (e.g. Enax et al, 2013;Poole, 1961;Finger et al, 2019;Dauphin & Williams, 2008;Kieser et al, 1993;Szewczyk & Stachewicz, 2020;Kundanati et al, 2019;Sato et al, 1990;Mishima et al, 2003), but limited dental histology data exist in other members of the order. Crocodile dental enamel is particularly thin (relative to dentine in other reptiles), reportedly in the order of 100-200 μm in C. porosus (Enax et al, 2013).…”