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Most researchers assume minimal impact of pretreatment on strontium isotope ratios ( 87 Sr/ 86 Sr) for bones and teeth, and methods vary tremendously. We compared 14 pretreatment methods, including no prep other than powdering enamel, ashing, soaking in water, an oxidizing agent (bleach or hydrogen peroxide) or acetic acid (0.1 M, 1.0 M, and 1.0 M buffered with calcium acetate), and a combination of these steps. We prepared and analyzed aliquots of powdered molar enamel from three proboscideans (one modern captive Indian elephant, Elephas maximus indicus ; one Pleistocene mastodon, Mammut americanum ; and one Miocene gomphothere, Afrochoerodon kisumuensis ). Each pretreatment was performed in triplicate and we measured 87 Sr/ 86 Sr, Sr concentration, and uranium (U) concentration, using the same lab space and instrumentation for all samples. Variability in 87 Sr/ 86 Sr and Sr and U concentrations was considerable across pretreatments. Mean 87 Sr/ 86 Sr across methods ranged from 0.70999 to 0.71029 for the modern tooth, 0.71458 to 0.71502 for the Pleistocene tooth, and 0.70804 to 0.70817 for the Miocene tooth. The modern tooth contained the least Sr and negligible U. The Pleistocene tooth contained slightly more Sr and measurable amounts of U, and the Miocene tooth had approximately 5x more Sr and U than the Pleistocene tooth. For all three teeth, variance in 87 Sr/ 86 Sr, Sr concentrations, and U concentrations among replicates was statistically indistinguishable across pretreatments, but there were apparent differences among pretreatments for the modern and Pleistocene teeth. Both contained relatively little Sr, and it is possible that small amounts of exogenous Sr from reagents, building materials or dust affected some replicates for some pretreatments. For the modern tooth, median 87 Sr/ 86 Sr varied considerably (but statistically insignificantly) across pretreatments. For the Pleistocene tooth, variability in median 87 Sr/ 86 Sr was also considerable; some pretreatments were statistically distinct but there were no obvious patterns among methods. For the Miocene tooth, variability in median 87 Sr/ 86 Sr was much smaller, but there were significant differences among pretreatments. Most pretreatments yielded 87 Sr/ 86 Sr and Sr concentrations comparable to, or lower than, untreated powder, suggesting selective removal of exogenous material with high 87 Sr/ 86 Sr. Further evaluation of the mechanisms driving isotopic variability both within and among pretreatment methods is warranted. Researchers should clearly report their methods and avoid combining data obtained using different methods. Small differences in 87 Sr/ 86 Sr could impact data interpretations, especially in areas where isotopic variability is low.
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The significance of enamel thickness in the teeth of Alligator mississippiensis and its diversity among crocodyliforms: Enamel thickness in crocodyliforms
Enamel is the hardest tissue in the vertebrate body. Although variation in enamel microstructure is often linked with diet, the gross proportions of the tissues that compose vertebrate teeth remain relatively unexplored in reptiles. To investigate the patterns of enamel thickness in crocodyliforms, we used micro‐computed tomography scanning to evaluate enamel thickness in teeth of Alligator mississippiensis from rostral, intermediate and caudal locations in the tooth row from an ontogenetic range of animals. We also evaluated enamel thickness in the derived teeth of several extinct crocodyliforms with disparate craniodental morphologies. Our data show that enamel thickness scales isometrically with skull length. We also show that enamel is relatively thicker in caudal teeth than teeth in more rostral positions, concordant with the higher bite forces they experience during feeding. We compared our data with existing enamel thickness data reported from dinosaurs and mammalian taxa to find that archosaurs have markedly thinner enamel than most mammals. These findings serve as a basis for future investigations into the diversity and function of the proportions of dental tissues.
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- Award ID(s):
- 1631684
- PAR ID:
- 10110156
- Date Published:
- Journal Name:
- Journal of Zoology
- ISSN:
- 0952-8369
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/jzo.12707
