Revealing enameloid shark chemistry at the nanoscale

Area of Science:

• Paleontology
• Biomineralization
• Geochemistry

Background:

• Shark teeth are valuable bio-archives for reconstructing past environments.
• Interpreting shark tooth chemistry relies on the assumption of consistent biomineralization processes over evolutionary time.

Purpose of the Study:

• To investigate the nanoscale chemical composition of modern and fossil shark enameloid.
• To test the assumption of constant biomineralization processes in shark tooth formation.

Main Methods:

• Atom probe tomography (APT) was used to analyze the chemical composition of enameloid at the nanoscale.
• Comparison of enameloid chemistry between modern (Isurus oxyrinchus) and fossil sharks (Striatolamia macrota, Macrorhizodus praecursor).

Main Results:

• Distinct chemical differences were observed at the core and grain boundaries of fluorapatite crystals within shark enameloid.
• Strontium enrichment was found at grain boundaries in all analyzed shark teeth.
• Differential distribution of magnesium, sodium, and iron was identified between modern and fossil shark teeth.
• Modern shark teeth showed magnesium and sodium at grain boundaries, while fossil teeth exhibited iron at boundaries and sodium at crystal cores.

Conclusions:

• Biomineralization processes for shark enameloid formation are not constant across shark phylogeny.
• Nanoscale chemical variations, including strontium, are linked to functional morphology.
• Magnesium and sodium roles in shark enameloid formation may parallel those in mammalian enamel.