Research ArticleCLIMATOLOGY

Repetitive mammalian dwarfing during ancient greenhouse warming events

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Science Advances  15 Mar 2017:
Vol. 3, no. 3, e1601430
DOI: 10.1126/sciadv.1601430
  • Fig. 1 Bighorn Basin and sample localities.

    The Bighorn Basin is located in northwestern Wyoming, USA. Upper Deer Creek (UDC), Gilmore Hill (GH), and White Temple (WT) stratigraphic sections are located within the McCullough Peaks region of the northern Bighorn Basin (outlined by a dashed box, see close-up in fig. S1).

  • Fig. 2 Stratigraphic framework.

    Lithostratigraphy, paleosol carbonate nodule isotope stratigraphy (δ13Cpc), biozonation, and magnetostratigraphy of the GH, WT, and UDC sections. The tan-shaded region highlights the body of ETM2 across all sections. The purple band represents the P2 marker bed, which can be visually traced across all outcrop sections in the field, and is associated with the most negative values of the ETM2 CIE. *Modified from Abels et al. (14).

  • Fig. 3 Arenahippus isotopes and tooth size in response to ETM2.

    Comparison of δ13C of pedogenic carbonate, δ13C of Arenahippus tooth enamel, and Arenahippus tooth size. Orange bands represent body of ETM2 and H2 CIEs. Purple band represents the P2 marker bed. (A) Isotopic data from paleosol carbonate nodules. UDC was aligned with GH and WT using the P2 bed (see Fig. 2). Arenahippus tooth enamel carbon isotope values (B) in association with Arenahippus tooth sizes (C) were collected across all three McCullough Peaks stratigraphic sections. Tooth size represents the observed M1 ln(tooth area) or the predicted M1 value based on tooth size regressions. Dark gray line represents a five-point moving average of all tooth size values, whereas the light gray shaded region represents the 95% CI for the mean. See figure legend for section and tooth position designations. Black horizontal bars on tooth sizes represent propagated analytical error (2σ).

  • Table 1 Binned average tooth size and body size estimates across ETM2.

    Bold P values are significant and are based on bootstrapping analyses described in Materials and Methods. P values were not determined for n < 5 [not applicable (N/A)].

    TaxonBinSample
    size (n)
    Average tooth size
    [ln(l × w)]
    95% Confidence
    interval*
    Body size
    estimate (kg)
    Natural log (ln)
    unit difference
    P value% Body size change
    between bins
    ArenahippusPre213.630.257.70Pre to mid−0.100.016−14.3%
    Mid293.530.306.60
    Post73.650.467.93Mid to post+0.080.032+20.1%
    Diacodexis†‡Pre212.630.141.62Pre to mid−0.100.010−15.0%
    Mid122.530.311.37
    Post42.710.571.83Mid to post+0.18N/A+32.9%
    Hyopsodus§Pre232.210.180.78Pre to mid+0.010.651+1.94%
    Mid142.220.250.79
    Post22.060.590.62Mid to post−0.16N/A−7.36%
    Cantius‡¶Pre222.850.252.51Pre to mid−0.030.315−4.26%
    Mid92.820.182.41
    Post12.772.22Mid to post−0.05N/A−7.79%

    *Equal to two SDs (2σ).

    †Body size calculation based on the study of Legendre (43), “artiodactyl + perissodactyl” tooth area–body size regression.

    ‡Post-ETM2 calculations for Diacodexis and Cantius are based on a single data point.

    §Body size calculation based on the study of Damuth (44), “nonselenodont ungulates” regression.

    ¶Body size calculation from Gingerich et al. (74) and Legendre (43), “primate” regressions.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1601430/DC1

      fig. S1. Section localities.

      fig. S2. Photos of P2 marker bed.

      fig. S3. Updated GH section.

      fig. S4. Stable isotopes of Arenahippus tooth enamel.

      fig. S5. ETM2 dwarfing patterns of Arenahippus, Diacodexis, Hyopsodus, and Cantius.

      fig. S6. Tooth size regression analyses.

      table S1. WT carbonate nodule δ13C.

      table S2. Updated GH carbonate nodule δ13C.

      table S3. Carbon and oxygen isotope data of Arenahippus tooth specimens.

      table S4. Stratigraphic levels and tooth size observations associated with each specimen in this study.

    • Supplementary Materials

      This PDF file includes:

      • fig. S1. Section localities.
      • fig. S2. Photos of P2 marker bed.
      • fig. S3. Updated GH section.
      • fig. S4. Stable isotopes of Arenahippus tooth enamel.
      • fig. S5. ETM2 dwarfing patterns of Arenahippus, Diacodexis, Hyopsodus, and Cantius.
      • fig. S6. Tooth size regression analyses.
      • table S1. WT carbonate nodule δ13C.
      • table S2. Updated GH carbonate nodule δ13C.
      • table S3. Carbon and oxygen isotope data of Arenahippus tooth specimens.
      • table S4. Stratigraphic levels and tooth size observations associated with each specimen in this study.

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