At the cutting edge: structural and elemental complexity of ziphodont tooth enamel in extant and fossil reptiles

Aaron LeBlanc*, Alexander Morrell, Slobodan Sirovica, Maisoon Al-Jawad, D. Labonte, Owen Addison

*Corresponding author for this work

Research output: Contribution to journalMeeting abstractpeer-review


Serrated, blade-shaped (ziphodont) teeth have evolved multiple times within Amniota, but they are mostly restricted to extinct taxa, including theropod dinosaurs. Given the prevalence of ziphodont teeth in the fossil record, our ability to test their mechanical properties would therefore benefit from sound understanding of the structural and chemical changes to fossilized dental tissues, as well as tissue-level comparisons with analogous teeth in extant reptiles.
Here we present structural, chemical, and nanomechanical analyses of the enamel and dentine of the teeth of Komodo dragons (Varanus komodoensis) and four species of extant crocodylians (Alligator mississippiensis, Crocodylus porosus, Tomistoma schlegelii, Osteolaemus tetraspis); we then compare these with fossil tyrannosaurid and crocodylian teeth from the Late Cretaceous of Southern Alberta. Synchrotron X-ray Fluorescence (SXRF) spectroscopy reveals that the serrations of V. komodoensis and the carinae of at least some crocodylian species are coated with an iron- and zinc-rich layer of enamel. This coating produces orange-coloured serrations and tooth tips in developing and functional teeth of V. komodoensis, and of the carinae of two of the studied crocodylians. Nanoindentation reveals that the enamel and dentine in these reptiles have comparable mechanical properties to mammal teeth tissues. We hypothesize that this thin pigmented layer along the cutting edges increases their resilience, analogous to iron pigmentation in the enamel of many mammal teeth, and to metal inclusions in the mandibles of many arthropods.
We also investigated enamel structure and chemistry in tyrannosaurid teeth. Scanning electron microscopy and synchrotron X-ray microdiffraction revealed that, unlike in V. komodoensis, tyrannosaurid enamel structure varies along the serrations and throughout the crown, with the serration enamel more closely resembling the wavy enamel found in some herbivorous dinosaurs. However, elemental and nanoindentation analyses showed that the dental tissues have undergone significant diagenetic alteration and cannot be directly compared to assess structure-function relationships. SXRF analysis confirmed anomalous distributions of trace elements within the enamel and dentine of tyrannosaurid teeth. By comparing these results with similar data from fossil and extant crocodylian teeth, we evaluate the possibility that tyrannosaurid teeth had pigmented tooth tips, similar to some extant reptiles.


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