1. A Preliminary Stable Isotope Ecology Based On Tooth Enamel For Latest Eocene and Earliest Oligocene Perissodactyls (Mammalia) From The White River Group Of Northwestern Nebraska Grant S. Boardman and Ross Secord Dept. of Earth and Atmospheric Sciences University of Nebraska-Lincoln

2.  Introduction and Main Questions

3. Eocene-Oligocene Transition(EOT) Drying/cooling in Central Great Plains associated with the Oi-1 glaciation. Proxies indicate change from dry forests/woodlands to drier woodlands/wooded grasslands (Evanoff et al., 1992; Hutchison, 1992; Retallack, 1992; Terry, 2001; Sheldon, 2009). No appreciable paleobotanical remains (barring phytoliths; Strömberg, 2005). Isotope ecology as indicator of vegetative habitats? Data from Zachos et al., 2001 Eocene Oligocene Oi-1

4. Question 1: What kind of habitats were WRF perissodactyls inhabiting in Nebraska during the EOT? woodlands shrublands

5. Question 2: Were taxa changing diets or habitats through this interval? See isotopic results of Zanazzi and Kohn (2008) and microwear results of Dewar (2008)

6.  Using Stable Isotopes in Paleoecology

7. Isotopes and δ notation δ 13 C or δ 18 O (‰) = [(R sample /R standard )-1]x 1,000 Where R sample and R standard are the 13 C/ 12 C and 18 O/ 16 O ratios. Tooth enamel carbonate values reported relative to (V-PDB) for carbon and (V-SMOW) for oxygen.

8. Carbon isotopes C3 Plants (trees, shrubs, and cool season grasses) C4 Plants (warm season grasses and sedges) Perrisodactyl Enamel/Diet Enrichment: ~+13‰ (Passey et al., 2005) Modified from Cerling et al., 1997

9. C3 Habitats Modeled values for C3 habitats assuming atmospheric δ 13 C value of -5.5‰ during EOT:  Mammals inhabiting closed canopy forests = -20.4‰ to -11.4‰  Inhabiting woodlands= -11.4‰ to -6.4‰  Inhabiting C3 grasslands=≥-6.4‰ [Cerling and Harris, 1999; Bocherens, 2003; Cerling et al., 2004; Codron et al., 2005; Passey et al., 2005]

10. Oxygen and water dependence Enamel body water derived from local surface water, water from food, and metabolic water (Kohn, 1996). Obligate drinker values reflect surface water values, drought tolerant taxa have higher δ 18 O (Levin et al., 2006). Browsers generally have higher δ 18 O than sympatric grazers (Kohn et al., 1996). Inhabitants of closed environments have lower δ 18 O (Cerling et al., 2004).

11.  Materials and Methods

12. Taxa Examined Megacerops, n=3 Mesohippus, n=30 Hyracodon, n=17 Total specimens analyzed = 62 Subhyracodon, n=7 © Carl Buell © Rob Barber Charles R. Knight Trigonias, n=5

13. Sampling Areas

14. Methods 3-4 mg of enamel drilled from tooth Chemically pretreated to remove organics and diagenetic carbonates. Samples run through mass spec by Lora Wingate at UMSIL. δ 13 C values reported against V-PDB standards. δ 18 O values reported against V-SMOW standards.

15.  Results

16. δ 13 C P<0.05 δ 13 C P<0.05

17. δ 18 O P<0.05

18. δ 13 C P<0.05

19.  Summary

20. Diet and Habitat preferences: Megacerops - δ 13 C -11.8‰ indicates marginal “closed-forest/riparian” habitat preference; δ 18 O 23.0‰ likely indicating browsing. Habitat lost in Orellan? δ 13 C ~-9.8‰ and -8.3‰ indicate all other taxa preferentially inhabiting “woodlands”. Mesohippus in more open areas; Hyracodon less water dependent. δ 18 O differences may indicate varying water dependence –or – that Subhyracodon and Trigonias could be grazing relative to the higher values of Hyracodon and Mesohippus (browser/mixed-feeders).* Subhyracodon potentially shifting towards more browsing in the Orellan or less water dependent.

21. Acknowledgements 21 George Corner, Greg Brown, Rob Skolnick, Ellen Stepleton and Bob Hunt. Committee Members: Tracy Frank, David Loope, R. Matt Joeckel, and Trish Freeman. Lora Wingate at the UMSIL Lab.

22. Any Questions? 22