22 Working Up an Apatite: Teeth as Paleo -Ecological and -Climatological Archives

Teeth are used as archives of paleo -ecological, -climatological, and -biological information. This session welcomes presentations using teeth as archives or testing new methods; from morphology, microwear, and histology to geochemical tools.

Sunday, 19 October 2025
8:00 AM - 12:00 PM
HBGCC, 304A

Combined Nitrogen and Calcium isotopes in Tyrannosaur tooth enamel reveal minor ontogenetic dietary trends

Paper number: 22-7
Program: Technical Sessions
Time: 9:40 AM – 9:55 AM

Authors

Abstract

From hatchling to full somatic adult, tyrannosaurs' body mass increased dramatically (from a few kilograms to thousands) as skull and jaw morphology also changed. These developments suggest an ontogenetic dietary shift, from smaller and agile prey (e.g., fish) to large, less mobile prey (e.g., herbivorous dinosaurs). Stable isotopes preserved in fossil teeth are a powerful archive of diet, averaging dietary signals over the period of tooth formation. Because tyrannosaurs continually shed and replaced their teeth, all ontogenetic stages are present in the fossil record. The nitrogenic isotope ratio (δ15N) of organisms is a well-established proxy for trophic level. Recently, the δ15N of enamel-bound organic matter has been confirmed to be preserved on million-year timescales. Calcium isotopes (δ44/40Ca) also offer trophic level information but are additionally impacted by the amount of bone ingested. In this work, we test for ontogenetic dietary shifts in tyrannosaurs using paired δ15N and δ44/40Ca measurements from a set of 21 Hell Creek Formation tyrannosaur teeth. We also present measurements from several potential prey taxa, including both terrestrial and aquatic food sources. We find evidence for only minor differences in the diets of small and large tyrannosaurs. The data may indicate that young tyrannosaurs have different sources for their nitrogen and calcium intake, with terrestrial sources dominating nitrogen and fish bones dominating calcium. The alternative is that gar, our sampled fish taxon, is not representative of the calcium and/or nitrogen isotopic composition of the broader fish population.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414785

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