Perez-Huerta Alberto, Samajpati Eshita, Farfan Gabriela A
Department of Geological Sciences, The University of Alabama, Tuscaloosa 35487, USA.
Alabama Museum of Natural History, The University of Alabama, Tuscaloosa 35487, USA.
Faraday Discuss. 2025 Sep 11;261(0):151-165. doi: 10.1039/d5fd00019j.
Shark teeth are considered excellent bio-archives because of their high abundance and preservation potential. Chemical proxies recorded by the teeth enameloid layers are used to interpret ecological and environmental parameters throughout the geological record. The use of these proxies relies on the assumption that biomineralization processes for enameloid formation have remained constant during shark evolution. Here, we test such an assumption by comparing the chemical composition at the nanoscale, using the technique of atom probe tomography (APT), of enameloid in modern and fossil shark teeth. Results indicate that there are clear differences in the chemistry at the core and inter-crystalline grain boundaries of fluorapatite crystals. These boundaries are enriched in strontium in all shark teeth, whereas there are differences in the distribution of magnesium, sodium, and iron. Teeth of the modern shark have magnesium and sodium distributed at the inter-crystalline grain boundaries. Teeth of Eocene fossil sharks, and , have a unique distribution of iron, at the inter-crystalline boundaries, and sodium, at the core of the crystals. This observation may indicate that biomineralization processes resulting in enameloid formation are not constant across the phylogeny of sharks. Overall, our findings strongly suggest that the enameloid content and distribution of magnesium, iron, strontium, and sodium are highly controlled by biomineralization processes. The role of magnesium and sodium seems to be similar in mammalian enamel and shark enameloid formation. Yet, nanoscale chemical differences, such as the presence of strontium in tooth enameloid, are likely associated to functional morphology.
鲨鱼牙齿因其丰富的数量和保存潜力而被视为优秀的生物档案。牙釉质层记录的化学指标被用于解读整个地质记录中的生态和环境参数。这些指标的使用依赖于这样一个假设，即在鲨鱼进化过程中，牙釉质形成的生物矿化过程保持不变。在此，我们通过使用原子探针断层扫描（APT）技术比较现代和化石鲨鱼牙齿牙釉质在纳米尺度上的化学成分，来检验这一假设。结果表明，氟磷灰石晶体的核心和晶界处的化学性质存在明显差异。在所有鲨鱼牙齿中，这些晶界都富含锶，而镁、钠和铁的分布存在差异。现代鲨鱼的牙齿中，镁和钠分布在晶界处。始新世化石鲨鱼和的牙齿在晶界处有独特的铁分布，在晶体核心处有独特的钠分布。这一观察结果可能表明，导致牙釉质形成的生物矿化过程在鲨鱼的系统发育过程中并非恒定不变。总体而言，我们的研究结果有力地表明，牙釉质的含量以及镁、铁、锶和钠的分布受到生物矿化过程的高度控制。镁和钠在哺乳动物牙釉质和鲨鱼牙釉质形成中的作用似乎相似。然而，纳米尺度的化学差异，如牙釉质中锶的存在，可能与功能形态有关。
