2026 Undergraduate Research Showcase

Rare Earth Element Uptake Rates Are (Mostly) Constant During Fossilization of Gar Fish Scales

Document Type

Student Presentation

Presentation Date

4-24-2026

Faculty Sponsor

Dr. Matthew Kohn

Abstract

Gar fish (Lepisosteidae) are a primitive fish whose scales consist of a bony plate covered in ganoine, a highly mineralized material similar to tooth enamel. Like teeth, gar scales have virtually no rare earth elements (REE) during life but take up REE upon fossilization. Here, we analyzed traverses across Cretaceous (~ 100 Ma) gar scales to investigate patterns of REE uptake. Gar fish scales were cut using a rock saw perpendicular to the ganoine layer and underlaying plate, then embedded in epoxy and polished. Trace element compositions were analyzed along traverses across the ganoine layer using inductively coupled plasma mass spectrometry (ICP-MS). Scanning electron microscope (SEM) imaging documented geometries and locations. All REE concentrations exceed initial biogenic compositions by about 2 to 5 orders of magnitude. All REE concentrations also decrease quasi-exponentially with distance from the ganoine surface, and nearly all REE show indistinguishable relative changes. However, some elements, especially La, Ce, and Y, show slightly flatter profiles, suggesting slightly faster diffusion rates. Similar REE profiles are commonly observed in fossil mammal teeth pointing to a common uptake mechanism of REE during fossilization.

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