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A 2015 comparison of shark teeth found a difference in where fluoroapatite occurred: in both dentin and enameloid in the extinct shark specimens examined, but only in enameloid in the recent shark specimens examined. The researchers proposed that environmental change after the Cretaceous might help explain the contrast; their study did not establish its cause.
What the study compared
The finding comes from the 2015 paper “Dental lessons from past to present: ultrastructure and composition of teeth from plesiosaurs, dinosaurs, extinct and recent sharks”, also covered by Chemistry World on 24 July 2015. The paper examined teeth from extinct marine reptiles and dinosaurs as well as extinct and recent sharks. Its shark comparison concerned the composition and structure of the specimens studied—not every species or tooth across shark history.
One terminology point matters: the mineralized covering of a shark tooth crown is called enameloid. It is not mammalian enamel. The tissue beneath it is dentin, so a statement about a mineral appearing in enameloid does not automatically apply to dentin.
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| Teeth examined in the 2015 study | Reported location of fluoroapatite |
|---|---|
| Extinct shark specimens | Both dentin and enameloid |
| Recent shark specimens | Enameloid; dentin composition differed |
This is a comparison of mineral composition by tissue layer in the sampled teeth. It does not mean all extinct sharks had the same mineral distribution, or that all living sharks share one composition. Nor does the finding say that shark tooth shape or anatomy changed in the same way as the chemistry.
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How the researchers studied the teeth
The paper’s abstract lists elemental analysis, scanning electron microscopy, X-ray powder diffraction with Rietveld refinement, and infrared spectroscopy. Together, these laboratory methods let researchers investigate elemental and mineral composition alongside microscopic structure. They are specialist analytical techniques, not a household test or a simple field identification method. The article does not provide a central percentage or sample count that would support a broader numerical claim.
What might explain the contrast—and what remains uncertain
The authors suggested that mineralization changed after the Cretaceous and that environmental changes might have made fluoroapatite less favorable. That is a proposed explanation, not a demonstrated cause. In the 2015 Chemistry World report, study author Matthias Epple speculated that fluoride scarcity in seawater and the demands of continual tooth replacement might help explain the composition of modern shark dentin. The report presents this as an open question, not a confirmed mechanism.
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The distinction is important: the measured result is a compositional difference in the teeth examined; the environmental account is an interpretation of why such a difference may have arisen. The comparison alone cannot establish what changed in the environment, when it changed, or whether one factor caused the mineral pattern.
Mineral chemistry is not the same as tooth shape or histology
Shark teeth can be compared along several separate dimensions: what minerals they contain, which tissue layer contains them, their microscopic tissue organization (histology), and their overall form. Similar-looking teeth do not necessarily have identical chemistry or microstructure.
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For example, a 2018 PLOS ONE study of Hemipristis used micro-CT and sections to describe pseudoosteodonty and distinguish it from lamniform osteodonty. That work concerns histology, not a direct replication of the 2015 fluoroapatite comparison. It is a reminder that shark tooth structure can be more varied than a simple extinct-versus-modern contrast suggests.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why later work still examines enameloid chemistry
A 2025 study, “Revealing enameloid shark chemistry at the nanoscale”, used atom probe tomography to compare modern and fossil shark enameloid and test the assumption that biomineralization processes remained constant through evolutionary time. Its stated research question shows why chemical proxies need careful interpretation across deep time; the abstract does not justify assuming a particular result beyond that question.
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The 2015 comparison therefore offers evidence about the specimens and methods in that study, while later work continues to scrutinize how reliably enameloid chemistry can be compared across ages. The two points are compatible: a reported pattern can be informative without settling every question about how mineralization evolved.
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- It says: the examined extinct shark teeth had fluoroapatite in both dentin and enameloid, whereas the examined recent shark teeth had it in enameloid, with a different dentin composition.
- It does not say: that every extinct and living shark follows that pattern, or that tooth shape and histology were unchanged.
- It suggests, but does not prove: that changes after the Cretaceous, potentially including environmental conditions, may have influenced mineralization.
Chemistry World also reported a 15–20 m estimated length for Megalodon based on corresponding tooth size. That contextual estimate is not the central result of the mineral-composition study.
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