DOI: 10.5061/dryad.nvx0k6f00
title: Data from: Oxygen isotope composition of teeth suggests endothermy and possible migration in some Late Cretaceous shark taxa from the Gulf Coastal Plain, USA

description: 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‰
 VSMOW in the Mooreville Chalk and 18.1‰ VSMOW in the Blufftown Formation).
 Excursions into brackish or freshwater habitats and thermal water-depth
 gradients are unlikely explanations for the lower P. mortoni and C.
 mantelli δ18Op values. The low P. mortoni δ18Op value is best explained by
 higher body temperature relative to surrounding temperatures due to active
 heating (e.g., mesothermy) or passive heating due to its large body size
 (e.g., gigantothermy). The low C. mantelli δ18Op values are best explained
 by a combination of mesothermy (e.g., active heating) and migration (e.g.,
 from the Western Interior Seaway, low latitude warmer waters, or the
 paleo-Gulf Stream), supporting the hypothesis that mesothermy evolved in
 lamniform shark taxa during the Late Cretaceous. If the anomalous P.
 mortoni δ18Op values are also driven by active thermoregulation, this
 suggests that mesothermy evolved independently multiple in families of
 Late Cretaceous sharks.
description: # 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 nomenclature for each specimen GeologicFormation- formation of specimen collection Member- member of specimen collection Locality- locality ID of specimen collection MicrocentrifugeLabel- individual measurement ID for each specimen sample ToothPosition- position on tooth of sample d18Op- stable oxygen isotope value Included- whether or not measurement was included in analyses st.dev-standard deviation n- number of samples per tooth se-standard error margin of error lowerCI- lower limit of confidence interval upperCI- upper limit of confidence interval off.avg- average value of offset between shark--Enchodus off.sd- standard deviation of average offset between shark--Enchodus The 'Supplemental Figures and Tables' document contains supplemental figures and tables that cited, but not included, in the main text. Supplemental Tables contain statistical information for the different species discussed in the main text. The Supplemental Figure contains detailed stable oxygen isotope information of multiple shark tooth specimens from a single individual.