DOI: 10.5061/dryad.w6m905qz3
title: Data from: Marine strontium isotopes preserved in fossil shark teeth calibrate Neogene land mammal evolution

description: Many Cenozoic terrestrial fossil sites worldwide rely on land mammal
 evolution (biochronology) for temporal calibrations. Within marine
 depositional environments, strontium isotope compositions from
 invertebrate fossils are often used for enhanced temporal resolution. Here
 we demonstrate that strontium isotope ratios from fossil shark tooth
 enameloid can quantitatively calibrate ages at sites containing both
 marine and non-marine fossils. Analysis of REEs in the same samples
 provides data for understanding the taphonomic histories of the specimens
 and allows for identification of specimens that were likely reworked.
 Using Neogene shark teeth, we resolve a ~600,000-year age difference
 between two late Miocene Florida sites previously binned together within
 the latest Hemphillian (Hh4) North American Land Mammal Age (NALMA) based
 solely on biochronology. This refinement brackets the Nme2 sea level
 lowstand, providing further calibration for the Great American Biotic
 Interchange (GABI) between South and North America. These examples
 emphasize the significance of strontium isotope ratios preserved in fossil
 shark teeth for global Neogene calibrations, especially in sites with
 marine/non-marine intercalations.
description: <strong><em>Experimental design.
 </em></strong>The MFS and PFBV experienced sea level
 fluctuations, accounting for the marine and terrestrial fossils collected
 from both sites. To account for nearshore fluvial influx of strontium,
 teeth from neritic sharks were chosen for SIS and REE analysis, for dating
 and taphonomic analysis, respectively. While some of these
 species<em> </em>may inhabit estuarine environments (Compagno
 et al., 2005), analysis of REEs aid us in ruling out the influence of a
 fluvial source of strontium that could obscure the marine strontium
 isotopic signature. Additional samples taken from terrestrial and marine
 mammalian fossil bone were analyzed for REE composition as a frame of
 reference for the REE signatures found in the shark teeth. McArthur et al.
 (2020) point out that terrestrial strontium input is assumed to be
 negligible, and this assumption can be scrutinized with the addition of
 REEs as described below. A total of 24 MFS shark teeth
 (5 species) and 25 PFBV shark teeth (5 species) were sampled from the
 University of Florida Vertebrate Paleontology (UF VP) collections (S1).
 Enameloid samples were collected via surface scratch technique using a
 dental grade carbide tip and Dremel tool, paying attention to avoid the
 dentine layer below. Previous work has demonstrated that the incorporation
 of more porous dentine can yield strontium values that deviate strongly
 from predicted values (Becker et al., 2008; Kocsis et al., 2016). Most
 samples were analyzed using approximately 20 mg of powdered
 enameloid.  Samples were prepared in a controlled
 cleanroom environment within the UF Department of Geological Sciences
 using refluxed Teflon vials and split for strontium collection and REEs
 following established protocols. Per protocol, the powdered sample weights
 were calculated and 50% HNO<sub>3 </sub>added to dissolve and
 clean the samples. Evaporated sample weights were recorded and resuspended
 with 5% HNO<sub>3</sub>/Re-Rh (8ppb) and the final
 preparations split for Sr and REE analysis.
 <strong><em>Strontium analysis.
 </em></strong>Samples were loaded into cation-exchange columns
 packed with strontium-specific resin (Eichrom Part #SR-B100-S) for
 extraction by loading 1 ml of 3.5 N HNO<sub>3</sub> followed
 by 100 µl of each sample into their respective columns. For sample weights
 lower than 20 mg, 200 µl of sample were loaded into the columns. Columns
 were rinsed five times with 100 µl of 3.5 HNO<sub>3</sub>,
 followed by a final wash with 1 ml of 3.5 HNO<sub>3</sub>.
 Strontium was then collected in newly refluxed Teflon vials by running 1.5
 ml of 4xH<sub>2</sub>O through the columns and then evaporated
 via hot plate. Prepared samples were analyzed on a Nu
 Plasma multicollector inductively coupled plasma mass spectrometer (MC
 ICPMS) at the University of Florida, using 100 µl of each sample mixed
 with 1,000 ml of 2% HNO<sub>3</sub>. The standard, NBS 987,
 was loaded after every four to six samples. The average
 <sup>87</sup>Sr/<sup>86</sup>Sr value and error
 calculated against standard NBS987 was 0.710240 ± 0.000020 (2 SD). The
 <sup>87</sup>Sr/<sup>86</sup>Sr values were
 corrected for mass bias, presence of Rb, and any interference. Corrected
 values were converted into ages using the LOESS Version 6 Table calibrated
 to the GTS2020 (Table 1; Howarth and McArthur, 1997; Gradstein et al.,
 2020; McArthur et al., 2020). Mean
 <sup>87</sup>Sr/<sup>86</sup>Sr ratios were
 calculated for each population (i.e., MFS, PFBV) and converted into
 numerical ages using the LOESS Version 6 Table calibrated to the GTS2020.
 Uncertainty is presented as 2s.e. (standard error) of the mean
 <sup>87</sup>Sr/<sup>86</sup>Sr ratio for each
 site converted to numerical ages.
 <strong><em>Rare Earth Element Analysis.
 </em></strong>For REE analysis, the prepped samples were run
 on a Thermo Finnigan ELEMENT 2 inductively coupled plasma mass
 spectrometer (University of Florida) and REE concentrations normalized to
 Post-Archean Australian Shale (PAAS) following McClellan’s protocol
 (McClellan, 1989). All but nine teeth (three from MFS and six from PFBV)
 were analyzed for REE composition. Additionally, samples were taken from
 the bones of mammals from each site (eight MFS terrestrial mammal samples,
 two from each of the four specimens, and one MFS cetacean; eight PFBV
 terrestrial mammal samples, two of which are from the same specimen, and
 two PFBV cetaceans) to compare against the REE signatures of the shark
 samples. Specific isotopes measured were <sup>139</sup>La,
 <sup>140</sup>Ce, <sup>141</sup>Pr,
 <sup>143</sup>Nd, <sup>149</sup>Sm,
 <sup>153</sup>Eu, <sup>157</sup>Gd,
 <sup>159</sup>Tb, <sup>163</sup>Dy,
 <sup>165</sup>Ho, <sup>166</sup>Er,
 <sup>169</sup>Tm, <sup>172</sup>Yb, and
 <sup>175</sup>Lu. Ce/Ce* and La/La* calculations followed the
 recent interpretations of Barret et al. (2023). All data analysis was
 conducted using R/R Studio programs (R Core Team, 2024), and the raw data
 and R code can be found in the Supplementary Materials section (Table S1
 and Data S1–S4).
description: # Marine strontium isotopes preserved in fossil shark teeth calibrate
 Neogene land mammal evolution
 [https://doi.org/10.5061/dryad.w6m905qz3](https://doi.org/10.5061/dryad.w6m905qz3) ## Description of the data and file structure ### **Datasets Include:** 1. Strontium Calculations for MFS and PFBV Shark Tooth Samples (File Name: Sr_Calcs_Shark_Teeth_MFS_PFBV.csv) * Contains the raw dataset for shark tooth enameloid sampled for 87Sr/86Sr from two Neogene Florida fossil localities, Montbrook (MFS) and Palmetto Fauna from the Bone Valley Region (PFBV) via ICPMS; * Variables: * Catalog Number: The unique identifier for a specimen sampled. * Specimen Code: The code given for each sample taken. * Taxon:  The organismal group sampled. * Site: The fossil locality from which the sample was collected. * Initial Sample Weight (g): The amount of powdered sample collected in grams. * Exp. Factor:  calculated fractionation factor using 86Sr/88Sr raw ratio * Exp. Factor Error: Error for the previous measurement. * 87/86 Raw: measured 87Sr/86Sr ratio corrected with the Exp. Factor * 87/86 Raw Error: Error for the previous measurement. * 86/88 Raw: measured raw, uncorrected 86Sr/88Sr ratio * 86/88 Raw Error: Error for the previous measurement. * 84/86 Raw: measured 84Sr/86Sr ratio corrected with the Exp. Factor * 84/86 Raw Error: Error for the previous measurement. * 84/88 Raw: measured 84Sr/88Sr ratio corrected with the Exp. Factor * 84/88 Raw Error: Error for the previous measurement. * Rb85 (V): 85Rb signal * Rb85 (V) Error: Error for the previous measurement. * 87/86 Rb Corr: measured 86Sr/87Sr ratio corrected with the Exp. Factor and corrected for 87Rb using the 85Rb signal * 87Sr/86Sr Corr: corrected 87Sr/86Sr ratio for deviations from the accepted value for NBS 987 87Sr/86Sr=0.71024 * LOWESS (V6) Mean Age (Ma): Mean age correlation from the LOWESS Version 6 Strontium Lookup Table ([Gradstein et al., 2020](https://www.sciencedirect.com/science/article/pii/S0031018224006874#bb0085); [McArthur et al., 2020](https://www.sciencedirect.com/science/article/pii/S0031018224006874#bb0180)) using the 87Sr/86Sr Corr values. * Sr (V): sum of the 88Sr, 87Sr, 86Sr,84Sr signals * Sr (V) Error: Error for the previous measurement. * 87Sr (V): 87Sr signal * 87Sr (V) Error: Error for the previous measurement. * Analysis Date: The calendar date samples were run on ICPMS. 2. Rare Earth Elements (REEs) PAAS Normalized for MFS and PFBV Shark and Mammal Samples (File Name: REE_Raw_Data_MFS_PFBV.csv) * Contains the raw dataset for shark tooth enameloid and mammalian bones sampled for REEs from two Neogene Florida fossil localities, Montbrook (MFS) and Palmetto Fauna from the Bone Valley Region (PFBV); * Variables: * Catalog Number: The unique identifier for a specimen sampled. * Specimen Code: The code given for each sample taken. * Taxon:  The organismal group sampled. * Site: The fossil locality from which the sample was collected. * La139 (ppm): 139La used for quantification of La concentrations, values in the column represent total ppm of La in parts per million. * Ce140 (ppm): 140Ce used for quantification of Ce concentrations, values in the column represent total ppm of Ce in parts per million. * Pr141 (ppm): 141Pr used for quantification of Pr concentrations, values in the column represent total ppm of Pr in parts per million. * Nd143 (ppm): 143Nd used for quantification of Nd concentrations, values in the column represent total ppm of Nd in parts per million. * Sm149 (ppm): 149Sm used for quantification of Sm concentrations, values in the column represent total ppm of Sm in parts per million. * Eu153 (ppm): 153Eu used for quantification of Eu concentrations, values in the column represent total ppm of Eu in parts per million. * Gd157 (ppm): 157Gd used for quantification of Gd concentrations, values in the column represent total ppm of Gd in parts per million. * Tb159 (ppm): 159Tb used for quantification of Tb concentrations, values in the column represent total ppm of Tb in parts per million. * Dy163 (ppm): 163Dy used for quantification of Dy concentrations, values in the column represent total ppm of Dy in parts per million. * Ho165 (ppm): 165Ho used for quantification of Ho concentrations, values in the column represent total ppm of Ho in parts per million. * Er166 (ppm): 166Er used for quantification of Er concentrations, values in the column represent total ppm of Er in parts per million. * Tm169 (ppm): 169Tm used for quantification of Tm concentrations, values in the column represent total ppm of Tm in parts per million. * Yb172 (ppm): 172Yb used for quantification of Yb concentrations, values in the column represent total ppm of Yb in parts per million. * Lu175 (ppm): 175Lu used for quantification of Lu concentrations, values in the column represent total ppm of Lu in parts per million. * Summed REE Concentration (ppm): Sum of all REE concentrations in parts per million. * PAAS Corrected La: Normalized REE concentration to PAAS (shale). * PAAS Corrected Ce: Normalized REE concentration to PAAS (shale). * PAAS Corrected Pr: Normalized REE concentration to PAAS (shale). * PAAS Corrected Nd: Normalized REE concentration to PAAS (shale). * PAAS Corrected Sm: Normalized REE concentration to PAAS (shale). * PAAS Corrected Eu: Normalized REE concentration to PAAS (shale). * PAAS Corrected Gd: Normalized REE concentration to PAAS (shale). * PAAS Corrected Tb: Normalized REE concentration to PAAS (shale). * PAAS Corrected Dy: Normalized REE concentration to PAAS (shale). * PAAS Corrected Ho: Normalized REE concentration to PAAS (shale). * PAAS Corrected Er: Normalized REE concentration to PAAS (shale). * PAAS Corrected Tm Normalized REE concentration to PAAS (shale). * PAAS Corrected Yb: Normalized REE concentration to PAAS (shale). * PAAS Corrected Lu: Normalized REE concentration to PAAS (shale). * Sm/La: Ratio of normalized Sm/La * Sm/Yb: Ratio of normalized Sm/Yb * La/Yb: Ratio of normalized La/Yb * Pr/Yb: Ratio of normalized Pr/Yb * La/Sm: Ratio of normalized La/Sm * Ce*g: Geometric log for cerium. * La*g: Geometric log for lanthanum * Ce/Ce*: Geometric calculation for cerium anomalies. * La/La*: Geometric calculation for lanthanum anomalies. * Log Sm/La: Log value of normalized Sm/La. MREE to LREE ratio. * Log Sm/Yb: Log value of normalized Sm/Yb. MREE to HREE ratio. * Log La/Yb: Log value of normalized La/Yb. LREE to HREE ratio. * Log Pr/Yb: Log value of normalized Pr/Yb. REE Spiderplot Data for MFS and PFBV Shark and Mammal Samples (File Name: REEPlotData.csv)  3. REE Spiderplot Data for MFS and PFBV Shark and Mammal Samples (File Name: REEPlotData.csv)  * Used to create REE spiderplots for MFS and PFBV sharks and mammals (Figs. 5-6) * Variables: * Catalog Number: The unique identifier number for a specimen sampled. * Specimen Code: The code given for each sample taken. * Taxon: The organismal group sampled. * Site: The fossil locality form which the sample is derived (MFS-Montbrook Fossil Site or PFBV-Palmetto Fauna Bone Valley). * Element: The lanthanide element. * Value: Normalized value given for the correlating REE element. Age: Mean age correlation from the LOWESS Version 6 Strontium Lookup Table ([Gradstein et al., 2020](https://www.sciencedirect.com/science/article/pii/S0031018224006874#bb0085); [McArthur et al., 2020](https://www.sciencedirect.com/science/article/pii/S0031018224006874#bb0180)) using the 87Sr/86Sr Corr values. * Specimen Cat: Indicator for specimen type: shark or mammal. * Label: Correlating specimen code label for plotting the data. 4.  REE Ratios for MFS and PFBV (File Name: REERatios.csv) * Used to create the plot of cerium and lanthanum anomalies from REE data (Fig. 7) * Variables: * Catalog Number: The unique identifier number for a specimen sampled. * Specimen Code: The code given for each sample taken. * Taxon: The organismal group sampled. * Site: The fossil locality form which the sample is derived (MFS-Montbrook Fossil Site or PFBV-Palmetto Fauna Bone Valley). * Rows F-S: The lanthanide elements (atomic numbers 51-71). * Sm/La: Ratio of Sm/La (MREE to LREE) * Sm/Yb:Ratio of Sm/Yb (MREE to HREE) * La/Yb: Ratio of La/Yb (LREE to HREE) * Pr/Yb: Ratio of Pr/Yb (MREE to HREE) * La/Sm: Ratio of La/Sm (LREE to MREE) * Ce/Ce*: Geometric calculation for cerium anomalies. * La/La*: Geometric calculation for lanthanum anomalies. * Ce*g: Geometric log for cerium. * La*g: Geometric log for lanthanum * Log Sm/La: Log value of normalized Sm/La. MREE to LREE ratio. * Log Sm/Yb: Log value of normalized Sm/Yb. MREE to HREE ratio. * Log La/Yb: Log value of normalized La/Yb. LREE to HREE ratio. * Log Pr/Yb: Log value of normalized Pr/Yb.  Missing data code: NA ## Code All code (R/R Studio; 2024) associated with the above datasets has been provided in the Supplementary Materials section of the manuscript.  ## Access information Links to publicly accessible Paleobiology Database: * [https://paleobiodb.org/#/](https://paleobiodb.org/#/) Links to publicly accessible University of Florida Vertebrate Paleontology Database: * [https://specifyportal.floridamuseum.ufl.edu/vp/](https://specifyportal.floridamuseum.ufl.edu/vp/) Data was derived from the following sources: * ICPMS (Department of Geological Sciences, University of Florida) * R and R Studio ([https://cran.rstudio.com/](https://cran.rstudio.com/))