Oxygen isotope composition of teeth suggests endothermy and possible migration in some Late Cretaceous shark taxa from the Gulf Coastal Plain, USA

We analyzed the oxygen isotope composition of biogenic apatite phosphate (δ18Op) in fossil tooth enameloid to investigate the paleoecology of Late Cretaceous sharks in the Gulf Coastal Plain of Alabama, U.S.A. We analyzed six different shark taxa from both the Mooreville Chalk and the Blufftown Formation. We compared shark δ18Op with the δ18Op of a co-occurring poikilothermic bony fish Enchodus petrosus as a reference for ambient conditions. E. petrosus tooth enamel δ18Op values are similar between formations (21.3‰ and 21.4‰ VSMOW, respectively), suggesting minimal differences in water δ18O between formations. Most shark taxa in this study are characterized by δ18Op values that overlap with E. petrosus values, indicating they likely lived in similar habitats and were also poikilothermic. Ptychodus mortoni and Cretoxyrhina mantelli exhibit significantly lower δ18Op values than co-occurring E. petrosus (P. mortoni δ18Op is 19.1‰ VSMOW in the Mooreville Chalk; C mantelli δ18Op is 20.2‰ VS..., , , # Data for Oxygen isotope composition of teeth suggests endothermy and possible migration in some Late Cretaceous shark taxa from the Gulf Coastal Plain, USA

[https://doi.org/10.5061/dryad.nvx0k6f00](https://doi.org/10.5061/dryad.nvx0k6f00)

## Description of the data and file structure

Supplemental Information contains two files: Appendix A. Supplemental Data (Excel spreadsheet) and Supplemental Figures and Tables (Word document).

The Appendix A. Supplemental Data file contains the raw oxygen isotope values, museum IDs, taxonomic information, and locality information for all specimens analyzed in the manuscript. Mean oxygen isotope values and other relevant statistical information at the species level are also included in this file.

**Variable Names and Descriptions**

SpecimenID- museum catalog number for each specimen

Order- taxonomic order for each specimen

Family- taxonomic family for each specimen

Species- taxonomic species for each specimen

ScientificName- binomial nomenc...