Data from: Marine strontium isotopes preserved in fossil shark teeth calibrate Neogene land mammal evolution
Data files
Jan 20, 2025 version files 110.17 KB
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README.md
10.12 KB
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REE_Raw_Data_MFS_PFBV.csv
21.96 KB
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REEPlotData.csv
45.19 KB
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REERatios.csv
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Sr_Calcs_Shark_Teeth_MFS_PFBV.csv
14.72 KB
Abstract
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.
README: Marine strontium isotopes preserved in fossil shark teeth calibrate Neogene land mammal evolution
https://doi.org/10.5061/dryad.w6m905qz3
Description of the data and file structure
Datasets Include:
- 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; McArthur et al., 2020) 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.
- 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;
- 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)
- 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);
- 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; McArthur et al., 2020) using the 87Sr/86Sr Corr values.
- Specimen Cat: Indicator for specimen type: shark or mammal.
- Label: Correlating specimen code label for plotting the data.
- Used to create REE spiderplots for MFS and PFBV sharks and mammals (Figs. 5-6)
- 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.
- Used to create the plot of cerium and lanthanum anomalies from REE data (Fig. 7)
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:
Links to publicly accessible University of Florida Vertebrate Paleontology Database:
Data was derived from the following sources:
- ICPMS (Department of Geological Sciences, University of Florida)
- R and R Studio (https://cran.rstudio.com/)
Methods
Experimental design. 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 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% HNO3 added to dissolve and clean the samples. Evaporated sample weights were recorded and resuspended with 5% HNO3/Re-Rh (8ppb) and the final preparations split for Sr and REE analysis.
Strontium analysis. 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 HNO3 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 HNO3, followed by a final wash with 1 ml of 3.5 HNO3. Strontium was then collected in newly refluxed Teflon vials by running 1.5 ml of 4xH2O 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% HNO3. The standard, NBS 987, was loaded after every four to six samples. The average 87Sr/86Sr value and error calculated against standard NBS987 was 0.710240 ± 0.000020 (2 SD). The 87Sr/86Sr 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 87Sr/86Sr 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 87Sr/86Sr ratio for each site converted to numerical ages.
Rare Earth Element Analysis. 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 139La, 140Ce, 141Pr, 143Nd, 149Sm, 153Eu, 157Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 172Yb, and 175Lu. 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).