carbon isotope analysis of mammalian herbivore...
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CARBON ISOTOPE ANALYSIS OF MAMMALIAN HERBIVORE TEETH FROM A 10 MILLION-YEAR-TIME SPAN, INCLUDING THE MID MIOCENE CLIMATIC OPTIMUM,
FLORIDA
By
MICHELLE MARIE BARBOZA-RAMIREZ
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2018
© 2018 Michelle Marie Barboza-Ramirez
To my parents, who instilled in me a sense of wonder and a love of learning.
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ACKNOWLEDGMENTS
I would like to begin by thanking my advisor, Bruce MacFadden, for not only
providing invaluable guidance for the development of this thesis but encouraging me to
pursue my projects in science communication, diversity, and women's studies. My other
committee members Andrea Dutton and Marta Wayne also helped me develop the skills
necessary for conducting this study, and I thank them for their patience and
encouragement.
I thank all contributors to the completion of this work. Sean Moran, Dr. Jay
O’Sullivan, Dr. Larisa DeSantis, and Dr. Bruce MacFadden contributed unpublished
isotope data to this study.
The curators of the vertebrate paleontology collections of the Florida Museum of
Natural History allowed me access to the materials used in this study, and Dr. Richard
Hulbert helped in identifying and cataloging material relevant to this study that had not
yet been accessioned. The members of my lab group provided much feedback
throughout the two years of developing and writing this thesis.
Funding for this work was provided by the National Science
Foundation (1115210, 1547229) in support of the Integrated Digitized Biodiversity
Collections (iDigBio) project at the University of Florida. Support was also provided by
the Vice President for Research and Department of Geological Sciences at the
University of Florida.
Finally, I would like to thank my family and my fiancé, who have supported me in
every way.
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TABLE OF CONTENTS page
ACKNOWLEDGMENTS .................................................................................................. 4
LIST OF TABLES ............................................................................................................ 7
LIST OF FIGURES .......................................................................................................... 8
LIST OF ABBREVIATIONS ............................................................................................. 9
ABSTRACT ................................................................................................................... 11
CHAPTER
1 INTRODUCTION ........................................................................................................ 13
Background ............................................................................................................. 13
Stable Isotopes ....................................................................................................... 15 A Review of δ13C .................................................................................................... 15
C3, C4, and CAM Photosynthesis ..................................................................... 15 δ13C values of Vegetation ................................................................................. 18 δ13C values of Fossil Tooth Enamel ................................................................. 20
A Review of δ18O .................................................................................................... 22 Paleoenvironment ............................................................................................ 22
Precipitation and Aridity .................................................................................... 22 Miocene Ecology and the Mid Miocene Climatic Optimum ..................................... 23
Cenozoic Climate Trends ................................................................................. 23 Origin and Expansion of C4 Vegetation ............................................................ 24
2 MATERIALS AND METHODS ................................................................................... 27
Sample Selection .................................................................................................... 27 Tooth Selection ................................................................................................ 27 Fossil Localities ................................................................................................ 29
Sample Pretreatment and Analysis ......................................................................... 33
3 RESULTS ................................................................................................................... 35
δ13C: Results ........................................................................................................... 35 δ13C values in Early to Mid Miocene Florida ..................................................... 35 δ13C values by Taxa and Feeding Habit ........................................................... 37
δ18O: Results .......................................................................................................... 39 Average δ18O values in Early to Mid Miocene Florida ...................................... 39
δ13C and δ18O by Site ............................................................................................. 41
4 DISCUSSION ............................................................................................................. 43
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Paleoecology of Mid Miocene Florida ..................................................................... 43
No Evidence for C4 Vegetation in Florida During the MMCO ............................ 43
Evidence of Open Canopy System ................................................................... 43 Aridity ............................................................................................................... 45 Local Meteoric Water ....................................................................................... 46
Herbivore Diets ....................................................................................................... 46 Ungulate Species Richness and Composition .................................................. 46
Further Research: Mean Annual Precipitation ........................................................ 46
5 CONCLUSION ........................................................................................................... 48
APPENDIX
A ISOTOPE DATA ........................................................................................................ 49
B VALIDITY OF LEGACY DATA ................................................................................... 56
C WOMENS STUDIES: THE FEMMES OF STEM ....................................................... 64
Summary ................................................................................................................ 64 Introduction ............................................................................................................. 64 Background ............................................................................................................. 65
Perceptions of Scientists .................................................................................. 65 History of Women in Science and Feminist Science Studies ........................... 66
Research ................................................................................................................ 67 Product And Press .................................................................................................. 68
Mentorship .............................................................................................................. 70 Conclusion .............................................................................................................. 70
LIST OF REFERENCES ............................................................................................... 72
BIOGRAPHICAL SKETCH ............................................................................................ 85
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LIST OF TABLES
Table page 2-1 Taxonomic representation of mammalian herbivores from 7 Mid Miocene
sites in Florida. ................................................................................................... 28
3-1 Average carbon isotope values of sites sampled................................................ 35
3-2 Results of Kruskal-Wallis rank sum test on the δ13C data from all sites under study. .................................................................................................................. 37
3-3 Average oxygen isotope values of sites sampled. .............................................. 40
3-4 Results of Kruskal-Wallis rank sum test on the δ18O data from all sites under study. .................................................................................................................. 41
B-1 Taxonomic representation of mammalian herbivores resampled from the late Miocene Love site in Florida. .............................................................................. 57
B-2 Results of Kruskal-Wallis rank sum test on the δ18O data from all sites under study. .................................................................................................................. 59
B-3 Results of Kruskal-Wallis rank sum test on the δ18O data from all sites under study. .................................................................................................................. 60
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LIST OF FIGURES
Figure page 1-1 Histogram showing normal distribution of δ 13C values from C3 and C4 plants.. . 18
1-2 Average carbon isotope values in terrestrial foodwebs for herbivorous mammals. ........................................................................................................... 19
2-1 Chronologic scale and map of Early to Mid Miocene Fossil Sites in Florida. ...... 30
3-1 Box and whisker plot for δ13C (V-PDB) values of sites sampled.. ....................... 36
3-2 δ13C (V-PDB) values of herbivore tooth enamel by feeding habit. ..................... 39
3-3 Box and whisker plot for δ18O (V-PDB) values of sites sampled. Dark orange: Northern site, light orange: Southern site. .......................................................... 40
3-5 δ13C (V-PDB) plotted against δ18O (V-PDB), by site. ......................................... 42
4-1 Variation of δ13C values in plants, reflected in δ13C enrichment of herbivores feeding on vegetation.. ....................................................................................... 44
4-2 Variation of δ18O values in plants, reflected in δ18O enrichment of herbivores feeding on vegetation.. ....................................................................................... 44
4-3 Interpretation of mean annual precipitation based on carbon isotope composition of fossil tooth enamel.. .................................................................... 47
B-1 Original δ13C data compared with new δ13C data. .............................................. 59
B-2 Original δ18O data compared with new δ18O data. .............................................. 60
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LIST OF ABBREVIATIONS
CAM Crassulacean acid metabolism, also referred to as the CAM photosynthesis carbon fixation pathway
FLMNH Florida Museum of Natural History
M1 Upper first molar
m1 Lower first molar
M2 Upper second molar
m2 Lower second molar
M3 Upper third molar
m3 Lower third molar
Ma Millions of Years
MAP Mean Annual Precipitation
MMCO Mid Miocene Climatic Optimum
NALMA North American Land Mammal Age
P4 Upper fourth premolar
p4 Lower fourth premolar
pCO2 Partial pressure of carbon dioxide
UF Denotes specimen housed in the collections of the Florida Museum of Natural History at the University of Florida
UF/FGS Denotes specimen housed in the collections of the Florida Museum of Natural History at the University of Florida, accessioned from the Florida Geologic Society
UF/TRO Denotes specimen housed in the collections of the Florida Museum of Natural History at the University of Florida, accessioned from the Timberlane Research Organization
V-PDB Vienna Pee Dee Belemenite, international reference standard for reporting isotope values
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δ 13C abundance of 13C relative to 12C, reported in parts per mil (‰) relative to V-PDB
δ 18O abundance of 18O relative to 16O, reported in parts per mil (‰) relative to V-PDB
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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science
CARBON ISOTOPE ANALYSIS OF MAMMALIAN HERBIVORE TEETH FROM A 10
MILLION-YEAR-TIME SPAN, INCLUDING THE MID MIOCENE CLIMATIC OPTIMUM, FLORIDA
By
Michelle Marie Barboza-Ramirez
August 2018
Chair: Bruce MacFadden Major: Geology
Stable carbon and oxygen isotopes of fossil tooth enamel are used here as a
proxy to reconstruct the diets and ecology of terrestrial herbivores from Florida in a ten
million year time span covering the Mid Miocene Climatic Optimum (MMCO) in order to
better understand the effect of this global climate event on regional terrestrial ecology;
specifically its effect on the spread of C3 and C4 vegetation in the Southeastern US.
Specimens herbivorous mammals within the orders Perissodactyla, Artiodactyla, and
Proboscidea are analyzed across 7 localities spanning the Southern to Northern
boundaries of the state. The age of the sites ranges from late Early Miocene
(Hemingfordian) through Middle Miocene (Clarendonian), or about 18 Ma to 9.5 Ma
years, providing a view of Florida ecology in “steady state” preceding, during, and
following the event. Results show an average of less than a 2‰ change on average in
either carbon or oxygen isotopes from the sites throughout this period. Mean δ 13C
values across the sites range from -9.67‰ to - 11.75‰, indicating a dominant C3 diet
for the animals sampled, likely in open environments. In Florida, the effect of the MMCO
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is limited and there is no indication of an early radiation of C4 grasses prior to the
worldwide radiation of C4 dominated ecosystems around 8 Ma.
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CHAPTER 1 INTRODUCTION
Background
Stable isotope analysis of carbon and oxygen from fossilized bone and tooth
material is used by vertebrate paleontologists to understand paleodiet (Wang, Y.,
Cerling, 1994), paleoecology (MacFadden and Cerling, 1996; Clementz and Koch,
2001; MacFadden and Higgins, 2004), and paleoclimate (Bryant et al., 1994). Carbon
isotope values of animal tissue reflect the carbon signal in plants comprising the diet of
the animal being sampled (Quade, Cerling, et al., 1992; Wang, Y., Cerling, 1994; Koch
et al., 1997), while oxygen isotope values reflect the composition of water being drunk
by the animal (Bryant and Froelich, 1995), which in turn serves as a proxy for aridity
(Levin et al., 2006), and amount of precipitation (Dansgaard, 1964).
Organic collagen in bone is rarely found in fossils older than late Pleistocene age
(Van der Merwe, 1982) and the remaining mineral portion of the bone is highly porous,
making it prone to introduction of secondary chemicals such as carbonate dissolved in
groundwater which can alter its carbon values (Kohn and Cerling, 2002; Schoeninger
and DeNiro, 1982). Thus, analysis of dental apatite (hydroxylapatite) from fossilized
tooth enamel is most common. It is worth noting that δ18O values are more prone to
diagenetic alteration in biogenic apatite than δ13C (Kohn and Cerling, 2002).
This study looks at the results of carbon and oxygen isotopes from a sample of
mammalian herbivore teeth from taxa in terrestrial sites spanning the majority of the
Miocene throughout the state of Florida in order to examine the effects of the Mid
Miocene Climate Optimum (MMCO). The MMCO was a period of intense global
warming that spanned from 18.5 Ma to 14.5 Ma (Zachos et al., 2001; Barnosky et al.,
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2003), but has so far been examined mainly in the context of marine ecosystems. Using
the extensive vertebrate paleontology collections from the Florida Museum of Natural
History (FLMNH), this study will provide a record of terrestrial ecosystems in the period
leading up to, during, and following this global climate event.
A total of 203 samples of dental apatite from fossilized mammalian herbivore
teeth from 6 Miocene age Florida fossil sites (Table A-1) are included in this study. Two
well-studied sites serve as end members to the study: Thomas Farm (17.5 Ma) and the
Love Bone Bed (9.5 Ma). These sites are two of the richest samples of Tertiary
vertebrate life in eastern North America (Hulbert Jr., 2001). The other localities from
which specimens are analyzed do not have extensive publications associated with
them, but are mentioned in related works (Webb and Hulbert, 1986), field guides
(Morgan and Pratt, 1988; Morgan, 1989), and in a figure from Hulbert's Fossil
Vertebrate of Florida (2001).
The purpose of this paper is to present the results of carbon isotopic analysis
from mammalian herbivore teeth of middle Miocene Florida in order to examine how the
MMCO affected the terrestrial ecology of Florida. Specifically, this paper is interested in
exploring the response of C3 and C4 vegetation during a period of intense global climate
change. Current understanding of the spread of C4 vegetation is that while this pathway
evolved independently in various taxa throughout the Cenozoic, C4 dominated
ecosystems did not expand until the late Miocene; however, evidence for an earlier
radiation of these ecosystems has been presented. Given that the factors under which
C4 vegetation outcompetes C3 are the same factors being taken to extreme during the
MMCO, it is an interesting time to study. Previous isotope work of herbivorous
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mammals in Florida has examined the period preceding the MMCO (Moran, 2014;
O’Sullivan, 2013) and the period during which C4 ecosystems expand overall
(MacFadden, 1999; MacFadden and Cerling, 1996) , leaving a 10 million year gap in our
knowledge of the paleoecology and climate of Miocene Florida. An extensive collection
of specimens in the FLMNH makes this study possible. Though their representation in
published literature is scarce, fossils from this time period in Florida are not lacking.
Carbon isotopes sampled from specimens of fossil teeth will serve as a proxy for
understanding the ecology of mid Miocene Florida, and my expectation is to see a
significant shift in local δ13C and δ18O values in response to the MMCO.
Stable Isotopes
Stable isotope analysis is conducted by comparing the ratio of two isotopes from
an element to that of a laboratory standard. In this case, the abundance of 12C/13C or
16O /18O ratios to belemnites from the Vienna Pe Dee Belemnite (V-PDB). The
calculation for deriving these ratios is as follows:
δX = [(Rsample/Rstandard)−1] × 1000. (1-1)
Where X is the δ 13C or δ 18O value, and R represents the abundance of the
heavy isotope relative to the light isotope, reported per mil (‰) relative to V-PDB.
A Review of δ13C
C3, C4, and CAM Photosynthesis
Due to the differential fractionation of carbon between plant groups with different
methods of CO2 fixation, carbon isotope ratios of animal tissue such as bone collagen
and biogenic apatite are a distinct marker for the diet of herbivores (Tykot, 2004; Kohn,
1999; DeNiro and Epstein, 1978; Wang et al., 1994). Carbon fixation in vegetation is
possible by photosynthesis using the metabolic pathway of either C3, C4, or
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crassulacean acid metabolism (CAM) carbon cycles, each of which results in a distinct
δ12C /δ13C ratio in plants (O’Leary, 1981; Farquhar et al., 1989). This signal carries
through to the animals who eat them, and the predators who eat those animals in turn
(Ben-David and Flaherty, 2012).
Plants that evolved using C3 fixation predate plants using C4 and CAM fixation by
several hundred million years: C3 plants first appear in the Paleozoic, while the first C4
and CAM plants appear in the Cenozoic (Osmond et al., 1982; Monson, 1989;
Ehleringer and Monson, 1993). C4 and CAM photosynthesis are both derived from C3,
but each have evolved independently within different taxa (Christin et al., 2008) and
have adapted to account for shortcomings in the C3 plants– specifically, the inability to
successfully function in hot, dry conditions.
Plants using the C3 photosynthetic pathway, otherwise known as the Calvin
Cycle, include trees, shrubs, and cool season grasses. The carbon fixing enzyme
employed by these plants is ribulose biphosphate carboxylase (rubisco) (Ehleringer and
Monson, 1993). Rubisco is not completely efficient however, as it will fix O2 instead of
CO2 during photorespiration, despite the fact that this results in no glucose for the plant.
Rubisco’s affinity to O2 increases under warmer conditions, which is compounded by
the fact that under these same conditions a plants stomata will close. This is done to
preserve water from evaporating through its pores, but it also prevents CO2 from
diffusing in and O2 from diffusing out. Thus, C3 plants do best under moderate
conditions.
The C4 pathway, also called the Hatch-Slack Cycle, and the CAM pathway
evolved to minimize photorespiration, allowing plants to better survive in high-
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temperature and low-CO2 environments (Hatch, 1971). This is accomplished by
separating CO2 fixation and the Calvin Cycle into different cell types in C4 plants, and
separating these steps between night and day in CAM plants. CAM plants do not
account for a significant amount of vegetation consumed by herbivores, however, so
they will not be explored further in this study.
C4 plants includes tropical grasses, sedges, and economically important species
such as maize, sugarcane, sorghum, and switchgrass. C4 grasses currently dominate
wide regions of the Earth, and it is estimated that they account for up to 25% of global
annual terrestrial primary production (Still et al., 2003). The C4 photosynthetic pathway
results in an enrichment of the heavy carbon isotope 13C, resulting in a higher mean
δ13C value relative to C3 plants.
The history of C4 photosynthesis reveals that along with multiple origins, the
development of this mode of photosynthesis experienced reversals and demonstrated a
significant lag time between the evolution of the C4 pathway and the formation of C4
dominated ecosystems (Strömberg, 2005; Christin et al., 2008). One theory regarding
the dramatic change in vegetation of the late Miocene considers the effects of CO2.
While the C3 plants evolved in a CO2-rich atmosphere (Edwards, Osborne, et al., 2010),
C4 plants evolved in an environment where the global climate has been considerably
different. The depletion of atmospheric CO2 in the mid-Cenozoic negatively affected the
efficiency and rate of carbon uptake in C3 plants (Edwards, Osborne, et al., 2010) while
studies have shown that C4 species are favored in reduced atmospheric CO2
(Ehleringer et al., 1997). The Late Miocene, the time in which C4 grasslands expanded,
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has been shown to have undergone a worldwide reduction in CO2, correlating with this
hypothesis.
The distribution of vegetation in the world at present also reflects this line of
thought: plants with C3 photosynthetic pathways are concentrated at high latitudes and
altitudes which can provide them with high pCO2 while plants with C4 photosynthetic
pathways take over the tropical to subtropical lowlands, where heat and low pCO2
prevent C3 vegetation from thriving. Other literature, however, finds mean annual
temperature as the main factor governing the altitudinal distribution of C3 and C4 grass
species (Bremond et al., 2012).
δ13C values of Vegetation
The differences in the physiology of C3 and C4 plants results in distinct carbon
isotope signatures (Figure 1-1). The δ13C values of C4 plants range from -9‰ to -19‰
with a mean of -13.0‰ while C3 plants range from -22‰ to -35‰ with a mean of -
27.0‰ (Deines, 1980; Boutton, 1991; Ehleringer and Monson, 1993; Koch, 1998a;
MacFadden, 2000; Dawson et al., 2002; Fung et al., 1997).
Figure 1-1. Histogram showing normal distribution of δ 13C values from C3 and C4 plants. Values based on Cerling et al. (1997), figure based on Tipple and Pagani (2007).
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These values are reflected in the carbon isotopic composition of herbivores
(DeNiro and Epstein, 1978; Kohn, 1999) with a consistent enrichment factor of +14‰
(Figure 1-2) (Kohn and Cerling, 2002; MacFadden and Cerling, 1996). Because the
isotopic ranges of C3 and C4 plants do not overlap, the isotopic signatures of animals
with a pure C3 or C4 diet will also be distinct, and animals with intermediate δ13C values
can be interpreted as mixed feeders (Macfadden et al., 1999; Koch, 1998a; Cerling and
Harris, 1999).
Figure 1-2. Average carbon isotope values in terrestrial foodwebs for herbivorous mammals. Values based on Deines (1980), Cerling and Harris (1999), and (MacFadden and Cerling, 1996); figure based on Tykot (2004)
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While photosynthetic pathway is the main control on the carbon isotope values of
plants, it is not the only factor at play. The availability of water, light, and nutrients
affects photosynthetic rates, causing isotope signatures to vary even within plants using
the same pathway (Ben-David and Flaherty, 2012; O’Leary, 1981). An increase in light
availability and nutrient values will result in higher δ13C values, while an increase in
water availability results in lower δ13C values (Heaton, 1999; Farquhar et al., 1989).
These factors being controlled in part by local environment, it follows that a gradient of
δ13C values exists between individual biomes. Vegetation in temperate grasslands and
open canopy environments have less shade to protect them from heat and water stress,
resulting in higher δ13C values compared to vegetation within forested environments,
which experience not only higher levels of shade but also higher levels of humidity,
resulting in lower δ13C values (Van der Merwe, 1982; Cerling and Harris, 1999; Cerling
et al., 2004a). In what is referred to as the canopy effect, leaves in the upper canopy of
forests have 3-4‰ higher δ 13C values than vegetation in the undergrowth (van der
Merwe and Medina, 1991; Heaton, 1999; Cerling et al., 2004b). Variations due the
aforementioned factors may affect δ13C values by 1 or 2‰ (Heaton, 1999).
The isotopic composition of a plant is controlled not only by the isotope
fractionation accompanying CO2 incorporation and the factors affecting the health of the
plant, but by the isotopic composition of the CO2 source itself. When considering
isotope composition from fossils, climatic changes affecting the concentration of
atmospheric CO2 may also play a part in the interpretation of δ13C values.
δ13C values of Fossil Tooth Enamel
Carbon from feeding sources is incorporated into vertebrate tissue during
skeletal formation, thus the isotopic signature of vegetation is preserved in mammalian
21
bone, enamel, and dentine (Kohn, 1999; Ben-David and Flaherty, 2012; Longinelli,
1984; Clementz, 2012; DeNiro and Epstein, 1978). The dominant mineral composition
of this substance is Ca10(PO4)6(OH)2, where carbonate (CO3)-2 substitutes in place of
phosphate to form a common variation of apatite, hydroxylapatite. Because bone is
highly porous, it is prone to introduction of secondary chemicals such as carbonate
dissolved in groundwater which can alter its initial carbon isotope values (Schoeninger
and DeNiro, 1982; MacFadden and Cerling, 1996). Dentine and enamel are less
susceptible to diagenesis as dentine has a similar size crystalline structure but much
lower porosity than bone, and enamel has both larger crystalline structure and lower
porosity (Quade, Cerling, et al., 1992; MacFadden et al., 1994; Koch et al., 1997; Wang
et al., 1994; Kohn and Cerling, 2002).
The isotopic composition of bioapatite will reflect an enrichment factor specific to
the feeding habit of an animal. Studies show carnivores and small mammals undergo a
consistent enrichment factor of ~9‰ (Lee-Thorp et al., 1989; Koch, 1998a) while large
herbivores show a consistent offset of ~14‰ (Cerling and Harris, 1999; Kohn and
Cerling, 2002). The dietary habits of herbivores further affect the δ13C values recorded:
browsers feed on trees and shrubs, which primarily use the C3 photosynthetic pathway,
resulting in lower δ13C values, grazers feed on grasses, which at lower latitudes (<
~40°) primarily use the C4 pathway, resulting in higher δ13C values (Figure 1-2).
Therefore, for the analysis of herbivore diet interpretation of δ13C values is as follows:
> –2 ‰ : dominantly C4 feeders (grazing taxa)
–2 ‰ to –8 ‰ : intermediate feeders (grazing and browsing)
< -8 ‰ : dominantly C3 feeders (browsing taxa)
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A Review of δ18O
Paleoenvironment
While carbon isotope values recorded in an animals body serve as a proxy for
diet, oxygen isotope values reflect local precipitation via the water being ingested by an
animal; this in turn serves as a proxy for regional climates (Dansgaard, 1964; Longinelli,
1984; Bryant and Froelich, 1995; Fricke and O’Neil, 1996; Luz et al., 1984). The ratio of
18O to 16O is based on preferential evaporation: H2O16 evaporates more readily that the
heavier H2O18, resulting in water vapor and precipitation enriched in 16O and source
water enriched in 18O. Thus, an increase in precipitation will result in lower 18O values,
and warmer, drier conditions result in higher 18O values (Dansgaard, 1964; Rozanski et
al., 1993; Feranec and MacFadden, 2000).However, interpretation of oxygen isotopes is
difficult to disentangle, as δ18O values are influenced by multiple factors, including
aridity, temperature, water source, the weight of each which varies based on altitude,
latitude, distance from a coast, and seasonality.
Precipitation and Aridity
Furthermore, while δ18O values from terrestrial animals reflect water source,
different types of taxa reflect different water sources. Obligate drinkers, or taxa which
are dependent on liquid water, will reflect the δ18O composition of ingested rainwater
(Kohn, 1996) while taxa which acquire most of their water via the plant material they
ingest will reflect the relatively enriched in δ18O composition of plant leaf water (Kohn,
1996; Levin et al., 2006).
The main influence on δ18O composition of ingested rainwater is temperature
(Dansgaard, 1964), where increased temperatures result in increased precipitation and
therefore increased fractionation of δ18O, resulting in more positive δ18O precipitation
23
values at warmer temperatures and more negative δ18Oprecipitation values at cooler
temperatures. However, one must consider that change in temperature may be affected
not only by global climate, but factors such as elevation and latitude, the increase of
which result in lower δ18O values ((Dansgaard, 1964). Aridity, on the other hand, is the
main influence on δ18O composition of plant leaf water. Thus obligate drinkers and
drought resistant taxa will have an offset of δ18O values, each of which reflects a
different aspect of the same environment
Work on modern mammals has shown that an aridity index can be created by
examining the oxygen isotope values of tooth enamel against meteoric water values
(Levin et al., 2006), and this process has been extended to fossil mammals as well
(Yann et al., 2013).
Miocene Ecology and the Mid Miocene Climatic Optimum
Cenozoic Climate Trends
The general trend for the past 65 million years of Cenozoic climate is a transition
from the warm, ice free climate of the Mesozoic to a cool, glaciated climate, with
understanding of Cenozoic temperature based on reconstruction of deep sea oxygen
isotope records (Miller et al., 1987; Zachos et al., 2001). Despite the general cooling
trend throughout the Cenozoic, significant global climate anomalies took place; one of
these was a prolonged global warming event during the Miocene epoch referred to as
the Mid Miocene Climatic Optimum (MMCO). The extreme warming event of the MMCO
took place from ~18.5 - 14.5 Ma (Barnosky et al., 2003; Zachos et al., 2008, 2001), with
a peak at 17 Ma. During the MMCO, ocean temperatures increased in high to mid
latitudes as well as the deep ocean to 58 - 68°C (Lear et al., 2000; Böhme et al., 2007;
Zachos et al., 2008), leading to a major decline in Antarctic ice sheets.
24
The Miocene epoch represents a transitional time in Earth’s history when long
term Cenozoic cooling was intercut with a severe warming event – the MMCO –
followed by the establishment of modern terrestrial ecosystems around the world. But,
while evidence of MMCO warming in is clear in marine records, there has been less
study of MMCO warming on land and the effects it had on terrestrial biota.
Fossil flora from Europe provide evidence of evergreen forests from the early-
middle Miocene (Ivanov et al., 2011) and stomatal frequency data from fossil leaves in
Austria, the Czech Republic, and Germany show that during the MMCO, CO2 was
elevated to 500 ppm (Kurschner et al., 2008a). Phytolith data from South America show
an increase in vegetation immediately following the peak of the MMCO, followed by a
decline in leaf area index as the climate cooled once more (Dunn et al., 2015); and
carbon isotope data from fossil tooth enamel in Central America show exclusively C3
vegetation during the MMCO (MacFadden and Higgins, 2004).
In North America, paleosols (Retallack, 1997; Fox and Koch, 2003), phytolith
assemblages (Strömberg, 2004; Smiley et al., 2017), and carbon isotope data from
fossil herbivore teeth (MacFadden, 2000; Wang et al., 1994; MacFadden and Cerling,
1996) show a transition from C3 woodlands to C4 grass dominated ecosystems as
groups of herbivorous mammals in North America transitioned from primarily browsing
feeding methods to primarily grazing feeding methods to exploit the new grasslands
following the MMCO (Janis et al., 2004; MacFadden, 2000).
Origin and Expansion of C4 Vegetation
The origin of C4 grasslands is established in the Mid Miocene (Fox and Koch,
2003; Smiley et al., 2017), while the transition from C3 dominated to C4 dominated
ecosystems appears to have taken place at about 8 Ma (Thure E. Cerling et al., 1993;
25
Christin et al., 2008; Kurschner et al., 2008b; Vicentini et al., 2008). The apparently
synchronous timing and widespread occurrence of grassland expansion in tropical
regions suggested it was triggered by a single, global mechanism (Ehleringer et al.,
1997). One theory regarding the dramatic change in vegetation of the late Miocene
considers the effects of CO2. C3 vegetation originated in the Paleozoic, while C4
vegetation originated in the Cenozoic. While the C3 plants evolved in a CO2 rich
atmosphere (Edwards, Smith, et al., 2010), C4 plants evolved to survive in an
environment where the global climate is considerably different. The depletion of
atmospheric CO2 in the mid-Cenozoic negatively affected the efficiency and rate of
carbon uptake in C3 plants (Edwards, 2010), while studies have shown that C4 species
are favored in reduced atmospheric CO2 (Ehleringer et al., 1997). The Late Miocene,
the time in which C4 grasslands expanded dynamically, has been shown to have
undergone a worldwide reduction in CO2, correlating with this hypothesis (Tipple and
Pagani, 2007).
The distribution of vegetation in the world at present also reflects this line of
thought: plants with C3 photosynthetic pathways are concentrated at high latitudes and
altitudes which can provide them with high pCO2 while plants with C4 photosynthetic
pathways take over the tropical to subtropical lowlands, where heat and low pCO2
prevent C3 vegetation from thriving (Hartley 1973).
Current understanding of the spread of C4 grasses at this time is that higher
temperatures and lower concentrations of atmospheric CO2 played into the decline of C3
plants, and the rise of C4 ecosystems, but our understanding of this transition on local
scales, however, is not refined. Some authors believe this later shift is an
26
oversimplification, and that pockets of C4 grasses expanded earlier (Fox and Koch,
2003; Clementz and Koch, 2001).
Studies indicate the expansion of C4 grasslands occurred earlier at lower
latitudes, as the threshold for C3 photosynthesis is higher at warmer temperatures
(Macfadden et al., 1999). This indicates that while pCO2 played a role, regional controls
were equally important factors on the development of C4 dominated ecosystems (Tipple
and Pagani, 2007). Mean annual temperature governs the altitudinal distribution of C3
and C4 grass species (Bremond et al., 2012), while an increase in aridity and wind
strength during the late Miocene may have created space for C4 grasslands (Tipple and
Pagani, 2007).
Data from phytolith assemblages and δ13C records from paleosols imply grass C4
dominated habitats spread in the Northern Rockies by the early Miocene (Harris et al.,
2017), and carbon isotope data from tooth enamel of herbivorous ungulates in
California, Oregon, and Nebraska from the mid Miocene (12-10 Ma) show C4 plants as
a significant component of terrestrial vegetation (Clementz and Koch, 2001). However,
newer studies of carbon isotope data from tooth enamel of herbivorous ungulates of the
California Barstow Formation supporting the spread of C4 grasses as prominent in
middle Miocene Southern California (Feranec and Pagnac, 2013), seem to be refuted
as reflecting a false signal from water stressed C3 plants (Bowman et al., 2017).
Reviewing the 10-million-year span of fossils from Florida in this study will provide us
with the first view of regional environmental and ecological response in the
Southeastern United States.
27
CHAPTER 2 MATERIALS AND METHODS
Sample Selection
Tooth Selection
All specimens were selected from previously collected material stored in the
vertebrate paleontology collection of the FLMNH. Some material came from museum
led excursions, while other material was donated to the museum by avocational
paleontologists. Fossils were identified as close to species level as possible using
information from published biostratigraphic ranges (Tedford et al., 2004; Janis et al.,
1998) as well as reference material from the FLMNH.
The following criteria was put forth in order to avoid specimens that might skew
isotope values due to effects of fractionation or diagenesis. Specimens must be from
herbivores, as isotopic fractionation is less affected in herbivories than in carnivores and
omnivores (Krueger and Sullivan, 1984). Specimens of fossil teeth only are examined in
this study, as tooth enamel is more resistant to alteration than porous bone (Fricke and
O’Neil, 1996; Bryant et al., 1994). Only late forming teeth (molars and the fourth
premolar) were sampled, as previous studies have also shown that tooth position can
affect both carbon and oxygen ratios by several parts per mil (Bryant et al., 1996; Fricke
and O’Neil, 1996). In order to avoid false signals from intra-tooth variance teeth were
sampled from the same position and bulk samples were taken parallel to the growth
axis (Passey and Cerling, 2002). No teeth from juveniles were included in the study, as
unerupted or deciduous teeth carry the signal of the mother’s milk rather than an
external signal (Jenkins et al., 2001).
28
Isotopic data from previously conducted analysis that was incorporated into this
study was reviewed with the same selection process. Samples processed following
older methods were tested for validity (see appendix) and confirmed to be valid under
updated processes.
Based on availability of specimens and selection criteria, this resulted in viable
samples over 200 medium to large bodied Perrisodactyla, Artiodactyla, and
Probscideans (Table 2-1).
Table 2-1. Taxonomic representation of mammalian herbivores from 7 Mid Miocene sites in Florida.
Grandorder Ungulata
Order Proboscidea Family Equidae (continued)
Family Ambeledontidae (shovel tuskers) Calippus (2) Ambeledon (2) Hiparionini (2) Order Artiodactyla Nannippus (1) Family Camelidae (camels, llamas) Neohipparion (3) Camelidae (2) Merychippus (11) Procamelus 1 Miohippus (19) Family Merycoidodontinae (oreodonts) Parahippus (95) Merycoidodontinae undetermined (1) Pliohippus (3) Family Tayassuidae Protohippus (3) Prosthenops (1) Pseudhipparion (1) Order Perissodactyla Family Tapiridae (tapirs) Family Equidae (horses, zebras) Tapirus (1) Acritohippus (4) Family Rhinocerotidae (rhinoceroses) Anchitherium (6) Aphelops (2) Archaeohippus (21) Rhinocerotidae (2) Cormohipparion (10) Teleoceras (3) Numbers in parentheses indicate number of specimens from each taxa analyzed for δ13C and δ18O.
More detailed information provided in appendix table A-1.
Through funding provided by the integrated digitized biodiversity collections
(iDigBio), previously uncatalogued specimens were prepared, identified, and entered
into the FLMNH digital catalog. Notably, isotope data both collected for and produced
from this study were added to the museum catalog files (Appendix C).
29
Through collaboration with iDigBio, this data will become public ally accessible to
not only researchers at the Florida Museum, but any person who wishes to access the
iDigBio database. Attaching stable isotope data to vouchered museum specimens in
their digital catalogs is not yet standard practice among museums, but it is our hope the
development of iDigBio as a major database will encourage this practice as a means for
big data analysis.
Fossil Localities
A total of 11 Miocene age fossil localities from Florida were identified as being of
interest to this study (Figure 2-1), the fossils of which are all housed in the paleontology
collections at the Florida Museum of Natural History, at the University of Florida. Based
on the availability of viable samples, 4 sites were removed from the study, leaving 7
sites to be studied in total.
30
Figure 2-1: Chronologic scale and map of Early to Mid Miocene Fossil Sites in Florida. Orange points mark locations and surrounding areas from which samples were obtained. All specimens housed at the Florida Museum of Natural History.Sites in dark orange represent Northern localities, sites in light orange represent Southern localities, sites with strike through removed from study due to lack of appropriate fossils (see sample selection, chapter 2). Ages based on Tedford (2004). Abbreviations as follows: Ma – millions of years; NALMA – North American Land Mammal Age; He1 - Hemingfordian Interval 1 and He2 - Interval 2, Ba1 - Barstovian Interval 1 and Ba2 - Interval 2, Cl1 - Clarendonian Interval 1, Cl2 - Interval 2, and Cl3 - Interval 3.
31
The oldest and most well studied fauna of this time period is the late Early
Hemingfordian Thomas Farm site in North Florida. The 17-18 Ma age is estimated
based on biostratigraphy, specifically four mammals, whose age has been confirmed as
Early Miocene with indirect radiometric and paleomagnetic methods (Tedford et al.,
2004). The mammals are: the canid Metatomarctus, the mustelid Leptarctus, the bear
Phoberocyon, and the rhinoceros Floridaceras. The site was discovered in 1931
(Simpson, 1932) and was excavated under the care of the Harvard University Museum
of Comparative Zoology until the 1950s, when it was given to the University of Florida
where it continues to be actively excavated (Macfadden, 2017). Both macro and micro
fossils are found in the site, resulting in over 100 species of animals, mostly vetebrates,
having been identified from the site. Isotopic analysis of fossil teeth from the site began
in the 1990’s (Wang et al., 1994), and data from these studies will be incorporated here.
The 16 Ma North Florida Brooks Sink Fauna (UF locality number BF001) is
considered Late Hemingfordian based on biostratigraphy. Morgan and Pratt (1988)
provide an overview of the paleontology of the site. No previous isotopic analysis of
fossils from this site has been done, but no fossil teeth from this site met our criteria for
moving forward with isotopic analysis.
The North Florida Willacoochee Creek, South Florida Sweetwater Branch, and
Bird Branch represent Early Barstovian Florida. The Willacoochee Creek fauna was first
as part of a geochronological study of horses from Miocene Florida (Bryant, 1991), and
is dated to 15.5 ma years based on the presence of the small rodents Copemys,
Perognathus, Rakomeryx, and Ticholeptus as well as Sr-isotope ages. No carbon
isotope analysis has been conducted on fossils of any of these sites, and while no fossil
32
teeth from the Sweetwater Branch or Bird Branch met our criteria for moving forward
with isotopic analysis, there are viable fossils for sampling from the Willacoochee Creek
fauna.
The Bone Valley Formation in Central Florida, first discovered in the early 1900s
(Simpson, 1929, 1930) has produced four major faunal assemblages spanning in age
from Barstovian to Hemphillian. The oldest, the Bradley Fauna, is loosely dated to the
Late Barstovian, which is the least well represented NALMA in Florida. The Bradley
Fauna is first reported in Webb and Hulbert’s (1986) paper on the systematics and
evolution of Pseudhipparion. No full faunal list or isotope work has previously been done
from specimens in this site, but viable specimens were identified for analysis in this
study.
The 11 Ma South Florida Agricola Fauna is considered Early Clarendonian
(Morgan, 1989). Along with the Bradley Fauna, the Agricola Fauna is first reported in
the same 1986 paper by Webb and Hulbert. No previous isotopic analysis of fossils
from this site has been done, but viable specimens were identified for analysis in this
study.
The North Florida Suwannee River Mine straddles the Florida Georgia border.
Fossils of varying Miocene ages have been found in the Hamilton County mine and
donated by collectors to the museum; Clarendonian specimens from this mine come
from the Statenville Formation and are known as the Occidental Local Fauna. Morgan
first reported this early Clarendonian site in the Miocene paleontology and stratigraphy
of the Suwannee River Basin of North Florida and South Georgia, written for the 1989
guidebook for the annual field trip of the Southeastern Geological Society (Morgan,
33
1989). No previous isotopic analysis of fossils from this site has been published, but
viable specimens were identified for analysis in this study.
The 9.5 Ma North Florida Love Bone Bed from the Alachua Formation,
Hawthorne Group is considered Late Clarendonian (Cl3) age based on biochronologic
data (Webb et al., 1981; Tedford et al., 2004). Like the Thomas Farm site, the Love
Bone Bed has been studied extensively, with multiple papers on its geology and
paleontology published. Previous work on the 9.5 ma Love Site fauna, includes a
seminal paper by Webb et al. (Webb et al., 1981) describing the geology and
paleontology of the site. Subsequent papers highlight individual taxa from the site . Over
80 marine and terrestrial vertebrate taxa recognized, half of which are mammals
(Feranec and MacFadden, 2006). The variety of taxa from the site seems to indicate
that it represents more than one habitat, likely including open, riparian, and forest.
Previously published data from isotopic analysis of Love Bone Bed specimens will be
included in this study. Taxa sampled in these studies include rhinos, camels, equids,
proboscideans, and tapirs (MacFadden and Cerling, 1996; MacFadden, 1998; Feranec
and MacFadden, 2006).
Sample Pretreatment and Analysis
Sample pretreatment was conducted in the Stable Isotope Geochemistry
Laboratory of the FLMNH Vertebrate Paleontology Department. Because previous
studies have shown that cementum and dentine are prone to alteration by diagenesis
(Quade, Cerlinga, et al., 1992; Wang et al., 1994), the surface of each tooth was
prepared by removing excess cementum and soil with a drill, and 15mg of powdered
enamel only was collected from the base of tooth. The teeth were drilled on weighing
paper and the enamel powder was transferred to labeled 1.5 mL graduated
34
microcentrifuge vials. To remove organic surface contaminants, the samples were
treated with H2O2 for 1 hour without sonication, then rinsed three times with deionized
water. To remove secondary carbonate, the samples were treated with 0.1 N acetic acid
for a half hour without sonication, then rinses 3 times with deionized water. To facilitate
drying, the samples were then rinsed with methanol and left overnight.
The dried samples were then analyzed using the light stable isotope mass
spectrometer in Department of Geology at University of Florida in Finnigan mass
spectrometer coupled with a Kiel III carbonate preparation device. Carbon and oxygen
were measured relative to the NBS-19 standard, and converted to according the Pee
Dee Belemnite standard, as set by the Vienna Convention (Coplen, 2011). Analysis is
reported in per mil (‰).
35
CHAPTER 3 RESULTS
δ13C: Results
δ13C values in Early to Mid Miocene Florida
Enamel carbon isotope compositions over the 10 Ma interval examined ranged
from -5.96‰ to -15.11‰ (Table A-1), with the average carbon isotope values for all taxa
ranging from -9.53‰ to -11.79‰ between sites (Table 3-1, Figure 3-1).
Table 3-1. Average carbon isotope values of sites sampled. Site Specimens
Analyzed Average Age (MA)
Latitude Average
δ13C‰
Love Site 23 9.5 North -11.79 Occidental Fauna 5 11 North -9.89 Agricola Fauna 11 11.5 South -9.53 Bradley Fauna 9 13.5 South -10.23 Willacoochee Creek Fauna 17 15.5 North -10 Midway Quincy Fauna 4 16.5 North -10.18 Thomas Farm 143 17.5 North -10.88
36
Figure 3-1: Box and whisker plot for δ13C (V-PDB) values of sites sampled. Dark orange: Northern site, light orange: Southern site. Numbers indicate amount of specimens from each taxa sampled at that site.
37
Because the data are not normally distributed, a Kruskal-Wallis rank sum test
followed by a post test (Dunn’s Multiple Comparison) was used to explore the
differences between the study sites (Table 3-2), and it was concluded that the data
demonstrate statistically significant differences, meaning that there is a shift in δ13C
values throughout the time span.
Table 3-2. Results of Kruskal-Wallis rank sum test on the
δ13C data from all sites under study. chi-squared p value
Kruskal-Wallis 31.15 0.000024
The data resulting from this study show that throughout the Mid Miocene, carbon
values are consistently below -8‰, which is interpreted as reflecting purely C3
vegetation. It is worth noting that the average δ13C values of the C3 fauna does not
remain static throughout this period, however. There is an average of 1.43‰ enrichment
of δ13C between the Thomas Farm site (representing an environment before the
MMCO) and the Midway Quincy and Willacoochee Creek sites (representing
environments during the MMCO). Values remain an average of 1.18‰ higher than the
pre-MMCO Thomas Farm site for sites during and following the MMCO, until the nearly
10 million year younger Love Site (9.5 Ma), when δ13C values drop -11.75‰.
δ13C values by Taxa and Feeding Habit
Mean δ13C values by order are as follows: -10.07‰ for artiodactyla, -10.99‰ for
perissodactyla, and -11.9‰ for proboscidea. Mean δ13C values of individual taxa can be
found in Table 3-3 and by dietary habits in Figure 3-2.
38
Table 3-3: Average δ13C‰ of taxa sampled
Order Family Ge Diet n Average δ13C‰
Artiodactyla Camelidae Undetermined B 2 -8.06
Artiodactyla Camelidae Procamelus B 1 -11.2
Artiodactyla Tayassuidae Prosethnops M 1 -11.3
Artiodactyla Undetermined Undetermined B 1 -10.67
Artiodactyla Merycoidodontinae Undetermined M 1 -10.25
Perissodactyla Equidae Acritohippus isonesus G 3 -8.89
Perissodactyla Equidae Anchitherium clarenci B 3 -9.70
Perissodactyla Equidae Archaeohippus blackbergi B 21 -10.92
Perissodactyla Equidae Calippus martini G 4 -9.82
Perissodactyla Equidae Cormohipparion M 7 -10.66
Perissodactyla Equidae Hiparionini 2 -9.09
Perissodactyla Equidae Merychippus gunteri G 12 -10.15
Perissodactyla Equidae Miohippus B 19 -9.53
Perissodactyla Equidae Nanippus B 2 -8.62
Perissodactyla Equidae Neophipparion trampense G 1 -10.1
Perissodactyla Equidae Parahippus leonensis M 95 -11.42
Perissodactyla Equidae Protohippus perditus M 3 -12.06
Perissodactyla Equidae Psuedhipparion M 1 -11.19
Perissodactyla Equidae Pliohippus G 1 -12.1
Perisodactyla Rhinocerotidae Aphelops B 2 -10.87
Perisodactlya Rhinocerotidae Teleocereas B 3 -12.49 Perisodactyla Rhinocerotidae Undetermined B 2 -11.48
Perisodactyla Tapiridae Tapirus B 1 -13.3
Proboscidea Amebledontidae Ambeledon G 2 -11.9
For diet G: grazing, M: mixed, B: browsing. N represents number of taxa sampled.
Bulk δ13C compositions range from -8.06‰ to -13.3‰, indicating that the
herbivores sampled at these sties fed exclusively on C3 vegetation, likely in an open
habitat
39
Figure 3-2: δ13C (V-PDB) values of herbivore tooth enamel by feeding habit.
δ18O: Results
Average δ18O values in Early to Mid Miocene Florida
The average oxygen isotope values for each site range from -0.42‰ to +0.87‰
(Figure 3-2, Table 3-2) over the course of 10 ma. The data resulting from this study
show that throughout the Mid Miocene, oxygen values range just over 1.5‰. There is
less than a 1‰ shift in δ18O between the Thomas Farm site (representing an
environment before the MMCO) and the Midway Quincy and Willacoochee Creek sites
(representing environments during the MMCO). Values remain an average of 0‰
throughout the rest of the sites for the remainder of the period.
40
Table 3-4. Average oxygen isotope values of sites sampled. Site Specimens
Analyzed Average Age (MA)
Latitude Average
δ18O‰
Love Site 23 9.5 North -0.42 Occidental Fauna 5 11 North 1.13
Agricola Fauna 11 11.5 South 0.19
Bradley Fauna 9 13.5 South 0.05
Willacoochee Creek Fauna 17 15.5 North -0.10
Midway Quincy Fauna 4 16.5 North 0.20
Thomas Farm 143 17.5 North 0.08
Figure 3-3: Box and whisker plot for δ18O (V-PDB) values of sites sampled. Dark orange: Northern site, light orange: Southern site.
Because the data are not normally distributed, a Kruskal-Wallis rank sum test
and Dunn’s Multiple Comparison test was used to qualify the differences between the
41
study sites (Table 3-4), both of which conclude that there is no statistically significant
difference between the values in each site as compared to the other.
Table 3-5. Results of Kruskal-Wallis rank sum test on the δ18O data from all sites under study.
chi-squared p value
Kruskal-Wallis 6.267 0.393904
δ13C and δ18O by Site
The absolute δ13C and δ18O values of all specimens sampled are displayed in
Figure 3-5.
42
Figure 3-5: δ13C (V-PDB) plotted against δ18O (V-PDB), by site.
43
CHAPTER 4 DISCUSSION
Paleoecology of Mid Miocene Florida
No Evidence for C4 Vegetation in Florida During the MMCO
Based on the δ13C enamel values indicate of the herbivores examined, there is
no evidence of an early radiation of C4 vegetation in early-Mid Miocene Florida.
Including outliers, δ13C enamel values fall well within the range expected of animals with
a dominant or exclusive diet of C3 vegetation.
This is consistent with findings from other fossil studies (Quade, Cerlinga, et al.,
1992; MacFadden and Cerling, 1996; Clementz and Koch, 2001; Harris, 2016), carbon
isotopes of paleosols (Cerling et al., 1989), and molecular dating studies (Spriggs et al.,
2014) which show that C3 plants were the dominant flora in North America and most of
the world until the late Miocene ~7 Ma (Thure E. Cerling et al., 1993).
Evidence of Open Canopy System
Stable carbon isotopes can also be used to reconstruct biomes, especially when
taking into account the effect that closed canopy environments have on δ13C and δ18O
values (Figure 4-1, Figure 4-2). Closed canopy environments experience higher
humidity, higher precipitation, and higher shade, leading to less evaporative stress in
plants, which is expressed as an enrichment of 12C (Cerling et al., 1999, 2004a).
Conversely, open canopy woodlands to grassland environments experience higher
evaporation, less shade, and more water stress, leading to an enrichment of 13C
(Farquhar et al., 1989; Cerling et al., 2004a).
44
Figure 4-1: Variation of δ13C values in plants, reflected in δ13C enrichment of herbivores feeding on vegetation. Based values from Ehleringer (Ehleringer et al., 1986) and Figure 2 from Quade (Quade et al., 1995).
Figure 4-2: Variation of δ18O values in plants, reflected in δ18O enrichment of herbivores feeding on vegetation. Based on Figure 3 from Quade (Quade et al., 1995).
45
The data from the sites studied here indicate that mid Miocene Florida was covered by
an open canopy system nearer to a dense woodland savanna. This falls in line with
previous research which indicates that throughout North America, closed-canopy forest
environments were being replaced by open-canopy woodlands and grasslands (Harris
et al., 2017; Retallack, 2007; Janis et al., 2004; Strömberg, 2004). While grasslands are
today associated with C4 dominant vegetation, paleosol, pollen, and phytolith data from
western North America, the Northern Rocky Mountains, the Great Plains, and now the
Southeastern United States indicate that the woodlands and grasslands of the early to
mid-Miocene were primarily composed of C3 vegetation.
Aridity
Evaporation sensitive taxa are those animals who can survive on little to no
water, and get the majority of their water from plants, thus, the δ18O values of tooth
enamel from these animals can be interpreted as a reflection of aridity (Levin et al.,
2006; Yann et al., 2013). Comparing the difference between evaporation insensitive
taxa and evaporation sensitive taxa allows for the creation of an aridity index for a site
(Levin et al., 2006).
However, in order to reconstruct the aridity index of an environment from d18O
values of tooth enamel, one needs to have a significant sample of both evaporation
sensitive and evaporation insensitive taxa. Due to their dependence on liquid water,
Proboscideans and Rhinocerotidae are understood to be evaporation insensitive taxa
(Levin et al., 2006), while Camelidae are considered evaporation insensitive (DeSantis
and Wallace, 2008); these three taxa are the least well represented in the study. More
specimens would need to be collected and analyzed in order to allow analysis of aridity
at these sites.
46
Local Meteoric Water
Evaporation insensitive taxa are animals who need to ingest liquid water daily,
rather than survive from the water gleaned from their diet (plant water). Thus, the δ18O
values of the tooth enamel from these animals has been shown to reflect the 18O values
of local meteoric water (Levin et al 2006). Yann and DeSantis (2013) have shown that
we can apply this knowledge to the fossil record and interpret tayassuidae and tapiridae
as evaporation insensitive families. However, only two specimens out of all sites
sampled fit within these families, which is insufficient data for further interpretation.
Herbivore Diets
Ungulate Species Richness and Composition
The woodland environments of Mid Miocene North America serve as ideal
spaces for browsing taxa, as documented by the high species richness of browsing
ungulates as compared to modern environments (Janis et al., 2004). Toward the late
Micene, a shift is recorded from taxa with low-crowned teeth ideal for a browsing on
trees and shrubs in forests and woodlands to taxa with high-crowned teeth ideal for
grazing in open savannas such as the C4 dominated environments spreading at 8 Ma
(Strömberg, 2006; Janis et al., 2000). The composition of the taxa sampled supports
these views, as the majority are browsers and mixed feeders
Further Research: Mean Annual Precipitation
δ13C values of fossil tooth enamel can also be used to estimate mean annual
precipitation of paleoenvironments (Figure 5-1). Is increase in δ13C values has been
shown to correlate with a decrease in MAP (Kohn, 2010; Diefendorf et al., 2010), but
interpretation of MAP is not advisable in environments with C4 plants, as they can
confuse the signal (Kohn, 2010). Considering the pure C3 environment of the sites
47
examined here, the data gathered could be used to confidently estimate MAP of Early to
Mid Miocene Florida. In order to compare our data, further work must be done to correct
δ13C values for changes in atmospheric CO2, altitude, and latitude. Some studies
suggest correcting for pCO2 as well, but recent work from Kohn (2010) shows the effect
is not significant enough to affect interpretation of these values.
Figure 4-3: Interpretation of mean annual precipitation based on carbon isotope composition of fossil tooth enamel, corrected for altitude, latitude, and δ13C of atmospheric CO2 (δ13Catm). Figure based on Kohn, 2010, values based on Kohn, 2010 and Cerling and Harris, 1999.
48
CHAPTER 5 CONCLUSION
This study examined the stable carbon and oxygen isotope values from dental
apatite of herbivorous mammals in middle Miocene Florida. Specimens from 7 FLMNH
fossil locales spanning a 10 million year time span were examined to see how the global
climate change associated with the MMCO affected local Florida paleoecology and
paleoenvironment. δ13C values from taxa of all ages consistently reflect C3 flora,
showing no evidence for early radiation of C4 grasses in Florida prior to the worldwide
radiation of C4 dominated ecosystems around 8 Ma. Regardless of interpreted feeding
habit, the taxa sampled here show mean δ13C values indicating a dominant or pure C3
diet. Combined with the relatively enriched δ18O mean values, the space in which these
taxa were feeding can be interpreted as an open canopy woodland to grassland
environment. Browsers and mixed feeders are most common across the sites.
Despite the intense change in global climate associated with the MMCO, δ18O
values remain consistent across all the sites sampled, indicating the effects of MMCO
on land may have varied regionally. An interpretation of local aridity and meteoric water
based on the comparison of evaporation sensitive and evaporation insensitive taxa is
not possible due to low sample size of ideal taxa. However, because of the complete
lack of C4 signal in the sites studied, there is protentional to examine the MAP of early-
mid Miocene Florida using the δ13C values produced. Further work will need to be done
to in order to correct offset caused by changes in altitude, latitude, and atmospheric
CO2
49
APPENDIX A ISOTOPE DATA
This appendix provides a Table (A-1) showing the values of all isotope data collected for and analyzed in this study. This includes previously sampled specimens from MacFadden & Cerling (1996), MacFadden (1998), O’Sullivan (2013, unpublished), and Moran (2014). Table A-1. Isotopic values of fossil herbivore tooth enamel from Mid Miocene sites in Florida. Data provided by the following: 1996,
MacFadden & Cerling; 1998, MacFadden; 2013, O’Sullivan; 2014, Moran; 2017 and 2018, Barboza. All specimens housed at the Florida Museum of Natural History. Uppercase denotes upper dentition, lowercase denotes lower dentition; uncat, uncatalogued specimen.
Site Age (Ma)
Sample ID Taxon Sample Analyzed δ13C (V-PDB) ‰
δ18O (V-PDB) ‰
Love Site 9.5 UF uncat 2A Cormohipparion plicatile - 1994 -10.3 - Love Site 9.5 UF uncat 2B Neohipparion trampense - 1994 -10.1 - Love Site 9.5 UF uncat Aphelops M3 1996 -12.4 - Love Site 9.5 UF uncat Procamelus M1 1996 -11.2 - Love Site 9.5 UF 26162 Tapirus M2 1996 -13.3 - Love Site 9.5 UF 29044 Prosthenops M3 1996 -11.3 - Love Site 9.5 UF uncat Rhinocerotidae M 1996 -13.1 - Love Site 9.5 UF uncat Ambeledon M 1996 -12.2 - Love Site 9.5 UF uncat Ambeledon M 1996 -11.9 - Love Site 9.5 UF 32265 (123) Cormohipparion plicatile P4 2018 -10.27 0.42 Love Site 9.5 UF 32265 (124) Cormohipparion plicatile M1 2018 -11.95 2.76 Love Site 9.5 UF 403160 Teleoceras proterum M3 2018 -13.06 -0.28 Love Site 9.5 UF 27182 Teleoceras proterum p4 2018 -11.16 -1.17 Love Site 9.5 UF 403159 Teleoceras proterum M3 2018 -13.25 1.01 Occidental Mine 11 UF 50755 cf. Pseudhipparion P3 or P4 2017 -10.28 0.14 Occidental Mine 11 UF 408144 Calippus martini M3 2017 -9.82 1.58 Occidental Mine 11 UF 408293 Cormohipparion ingenuum p4 2017 -10.22 1.26 Occidental Mine 11 UF 408302 Calippus M3 2017 -8.92 1.77 Occidental Mine 11 UF 408803 Merycoidodontinae m3 2017 -10.25 0.88 Agricola Fauna 11 UF 98205 Nannippus M3 2017 -9.66 0.52 Agricola Fauna 11 UF 98366 Camelidae M3 2017 -8.95 1.28 Agricola Fauna 11 UF 107667 Psuedhipparion M3 2017 -11.19 2.22
50
Table A-1. Continued
Site Age (Ma)
Sample ID Taxon Sample Analyzed δ13C (V-PDB) ‰
δ18O (V-PDB) ‰
Agricola Fauna 11 UF 107848 Camelidae P4 2017 -8.06 -0.81 Agricola Fauna 11 UF 162908 Calippus martini M3 2017 -10.26 -1.5 Agricola Fauna 11 UF 217095 Hiparionini M3 2017 -9.18 -0.4 Agricola Fauna 11 UF 217125 Hiparionini M3 2017 -9 -0.75 Agricola Fauna 11 UF 217201 Cormohipparion plicatile P3 or P4 2017 -10.87 0.79 Agricola Fauna 11 UF 217172 Cormohipparion ingenuum P4 2017 -10.46 0.19 Agricola Fauna 11 UF 220200 Pliohippus pernix p3 or p4 2017 -9.08 0.23 Agricola Fauna 11 UF 211931 Cormohipparion M3 2017 -10.52 0.42 Agricola Fauna 11 UF 107668 Pseudhipparion M3 2017 -7.1 0.1 Bradley Fauna 12.5 UF/TRO 1685 Protohippus perditus M3 2017 -11.64 0 Bradley Fauna 12.5 UF/TRO 1686 Protohippus perditus P4 2017 -12.72 -0.73 Bradley Fauna 12.5 UF/TRO 1324 Pliohippus mirabilis P4 2017 -12.1 1.18 Bradley Fauna 12.5 UF 93292 Merychippus goorisi m3 2017 -9.4 -0.42 Bradley Fauna 12.5 UF 93295 Merychippus goorisi M3 2017 -10.5 0.1 Bradley Fauna 12.5 UF 93296 Merychippus goorisi M3 2017 -11.1 0.1 Bradley Fauna 12.5 UF/TRO 25545 Teleoceras medicornutum P4 2017 -9.85 -0.17 Bradley Fauna 12.5 UF/TRO 28953 Protohippus perditus M3 2017 -11.81 0.59
Willacoochee Creek 15.5 UF 221405 Anchitherium isonesus M3 2017 -8.9 -1.7 Willacoochee Creek 15.5 UF 217562 Acritohippus isonesus M3 2017 -11.5 -0.7 Willacoochee Creek 15.5 UF 221407 Acritohippus isonesus P3 or P4 2017 -10.4 0.8 Willacoochee Creek 15.5 UF 221427 Merychippus primus M3 2017 -9.4 1.1 Willacoochee Creek 15.5 UF 221419 Merychippus primus P4 2017 -10.3 0.2 Willacoochee Creek 15.5 UF 221408 Mercyhippus gunteri M3 2017 -10.4 -0.8 Willacoochee Creek 15.5 UF 114721 Merychippus gunteri M3 2017 -11.3 -0.5 Willacoochee Creek 15.5 UF 221426 Merychippus primus M3 2017 -10.3 -0.7 Willacoochee Creek 15.5 UF 221434 Artiodactyla M3 2017 -11.0 -0.6 Willacoochee Creek 15.5 UF 221402 Anchitherium clarenci M1 2017 -8.5 0.2 Willacoochee Creek 15.5 UF 217565 Aphelops P 2017 -10.9 -0.1 Willacoochee Creek 15.5 UF 221416 Merychippus gunteri P3 or P4 2017 -8.9 -1.6 Willacoochee Creek 15.5 UF 107522 - - 2017 -10.62 1.06 Willacoochee Creek 15.5 UF 116815 Dromomerycidae P4 2017 -9.41 -0.02 Willacoochee Creek 15.5 UF 98209 Nannippus M3 2017 -10.88 -0.05 Midway Quincy Fauna 16.5 UF 4980 Anchitherium clarencei p3 or p4 2017 -10.54 0.61 Midway Quincy Fauna 16.5 UF 9934 Merychippus gunteri m3 2017 -10.2 0.5
51
Table A-1. Continued
Site Age (Ma)
Sample ID Taxon Sample Analyzed δ13C (V-PDB) ‰
δ18O (V-PDB) ‰
Midway Quincy Fauna 16.5 UF 9938 Merychippus gunteri m3 2017 -10.3 0.2 Midway Quincy Fauna 16.5 UF/FGS 9960 Merychippus gunteri m3 2017 -9.6 -0.5 Thomas Farm 19 UF/FGS 5243 Anchitherium clarenci m1 2017 -10.0 0.7 Thomas Farm 19 UF uncat 1A Parahippus leonensis - 1994 -10.80 - Thomas Farm 19 UF uncat 1B Archaeohippus blackbergi - 1994 -8.80 - Thomas Farm 19 001 A Archaeohippus - 2014 -12.51 -1.66 Thomas Farm 19 001 B Archaeohippus - 2014 -11.43 1.36 Thomas Farm 19 001 C Archaeohippus - 2014 -11.49 -1.50 Thomas Farm 19 002 A* Archaeohippus - 2014 -11.49 -1.50 Thomas Farm 19 002 B Archaeohippus - 2014 -11.56 0.96 Thomas Farm 19 002 C Archaeohippus - 2014 -10.83 1.62 Thomas Farm 19 003 A Archaeohippus - 2014 -9.77 2.55 Thomas Farm 19 003 B Archaeohippus - 2014 -10.37 2.00 Thomas Farm 19 003 C Archaeohippus - 2014 -10.46 -1.92 Thomas Farm 19 004 A Archaeohippus - 2014 -10.35 1.32 Thomas Farm 19 004 B Archaeohippus - 2014 -15.11 -9.93 Thomas Farm 19 004 C Archaeohippus - 2014 -8.86 4.27 Thomas Farm 19 005 A Archaeohippus - 2014 -11.07 -0.59 Thomas Farm 19 005 B Archaeohippus - 2014 -9.93 2.69 Thomas Farm 19 005 C Archaeohippus - 2014 -10.22 1.19 Thomas Farm 19 005 D Archaeohippus - 2014 -9.85 2.27 Thomas Farm 19 006 A Archaeohippus - 2014 -12.51 -2.09 Thomas Farm 19 006 B Archaeohippus - 2014 -10.90 1.03 Thomas Farm 19 006 C Archaeohippus - 2014 -11.18 0.00 Thomas Farm 19 006 D Archaeohippus - 2014 -10.67 -0.16 Thomas Farm 19 007 A Miohippus - 2014 -9.84 -2.99 Thomas Farm 19 007 B* Miohippus - 2014 -9.84 -2.99 Thomas Farm 19 008 A Miohippus - 2014 -9.01 -5.29 Thomas Farm 19 008 B Miohippus - 2014 -8.80 -6.97 Thomas Farm 19 008 C Miohippus - 2014 -9.93 -4.13 Thomas Farm 19 009 A* Miohippus - 2014 -9.93 -4.13 Thomas Farm 19 009 B Miohippus - 2014 -11.42 -4.31 Thomas Farm 19 009 C Miohippus - 2014 -11.42 -4.31 Thomas Farm 19 010 A Miohippus - 2014 -9.61 -4.76
52
Table A-1. Continued
Site Age (Ma)
Sample ID Taxon Sample Analyzed δ13C (V-PDB) ‰
δ18O (V-PDB) ‰
Thomas Farm 19 010 B Miohippus - 2014 -8.55 -1.38 Thomas Farm 19 010 C Miohippus - 2014 -9.36 -4.34 Thomas Farm 19 011 A Miohippus - 2014 -8.79 -4.36 Thomas Farm 19 011 B Miohippus - 2014 -9.36 -3.91 Thomas Farm 19 011 C Miohippus - 2014 -9.34 -2.67 Thomas Farm 19 011 D* Miohippus - 2014 -9.34 -2.67 Thomas Farm 19 012 A Miohippus - 2014 -8.87 -2.92 Thomas Farm 19 012 B Miohippus - 2014 -8.82 -3.41 Thomas Farm 19 012 C Miohippus - 2014 -8.94 -2.90 Thomas Farm 19 012 D* Parahippus leonensis - 2014 -8.94 -2.90 Thomas Farm 19 0013 B Parahippus leonensis - 2014 -10.70 1.40 Thomas Farm 19 0013 C Parahippus leonensis - 2014 -10.02 2.53 Thomas Farm 19 0014 A Parahippus leonensis - 2014 -10.52 2.38 Thomas Farm 19 0014 B Parahippus leonensis - 2014 -10.52 2.38 Thomas Farm 19 0014 C Parahippus leonensis - 2014 -10.10 -0.16 Thomas Farm 19 0015 A Parahippus leonensis - 2014 -9.95 -0.32 Thomas Farm 19 0015 B Parahippus leonensis - 2014 -10.63 -2.67 Thomas Farm 19 0015 C Parahippus leonensis - 2014 -9.99 -1.24 Thomas Farm 19 0016 A Parahippus leonensis - 2014 -9.62 0.89 Thomas Farm 19 0016 B Parahippus leonensis - 2014 -11.07 -3.22 Thomas Farm 19 0016 C Parahippus leonensis - 2014 -9.79 0.25 Thomas Farm 19 0017 A Parahippus leonensis - 2014 -11.34 -2.23 Thomas Farm 19 0017 B Parahippus leonensis - 2014 -10.11 0.81 Thomas Farm 19 0017 C Parahippus leonensis - 2014 -10.40 -0.90 Thomas Farm 19 0017 D Parahippus leonensis - 2014 -10.08 0.16 Thomas Farm 19 0018 A Parahippus leonensis - 2014 -11.94 -1.97 Thomas Farm 19 0018 B Parahippus leonensis - 2014 -11.94 -1.97 Thomas Farm 19 0018 C Parahippus leonensis - 2014 -10.08 1.23 Thomas Farm 19 0018 D Parahippus leonensis - 2014 -10.50 0.40 Thomas Farm 19 60 Parahippus leonensis m2 2014 -12.35 2.03 Thomas Farm 19 60 Parahippus leonensis m2 2014 -11.18 1.26 Thomas Farm 19 UF 40020 Parahippus leonensis m2 2014 -12.01 1.71 Thomas Farm 19 UF 40020 Parahippus leonensis m2 2014 -11.76 0.88 Thomas Farm 19 UF 44815 Parahippus leonensis m3 2014 -13.11 -0.69
53
Table A-1. Continued
Site Age (Ma)
Sample ID Taxon Sample Analyzed δ13C (V-PDB) ‰
δ18O (V-PDB) ‰
Thomas Farm 19 UF 44815 Parahippus leonensis m3 2014 -11.62 0.04 Thomas Farm 19 UF 95364 Parahippus leonensis m1 2014 -12.88 0.84 Thomas Farm 19 UF 95364 Parahippus leonensis m1 2014 -12.16 -0.96 Thomas Farm 19 UF 99392 Parahippus leonensis m2 2014 -11.84 2.7 Thomas Farm 19 UF 155373 Parahippus leonensis m3 2014 -12.68 2.47 Thomas Farm 19 UF 155373 Parahippus leonensis m3 2014 -12.1 1.07 Thomas Farm 19 UF 157579 Parahippus leonensis m2 2014 -11.2 1.14 Thomas Farm 19 UF 157579 Parahippus leonensis m2 2014 -10.21 1.59 Thomas Farm 19 UF 158290 Parahippus leonensis m3 2014 -13.23 -1.49 Thomas Farm 19 UF 158290 Parahippus leonensis m3 2014 -12.63 -0.91 Thomas Farm 19 UF 164767 Parahippus leonensis m2 2014 -11.8 1.64 Thomas Farm 19 UF 164767 Parahippus leonensis m2 2014 -11.44 1.54 Thomas Farm 19 UF 176616 Parahippus leonensis m1 2014 -13.09 0.54 Thomas Farm 19 UF 176616 Parahippus leonensis m1 2014 -10.96 0.6 Thomas Farm 19 UF 192280 Parahippus leonensis m3 2014 -11.7 0.38 Thomas Farm 19 UF 192280 Parahippus leonensis m3 2014 -11.75 0.81 Thomas Farm 19 UF 192310 Parahippus leonensis m3 2014 -11.75 1.04 Thomas Farm 19 UF 192310 Parahippus leonensis m3 2014 -10.92 2.9 Thomas Farm 19 UF 201702 Parahippus leonensis m3 2014 -10.86 1.98 Thomas Farm 19 UF 201702 Parahippus leonensis m3 2014 -11.33 1.53 Thomas Farm 19 UF 203391 Parahippus leonensis m3 2014 -11.42 1.45 Thomas Farm 19 UF 203391 Parahippus leonensis m3 2014 -11.06 2.24 Thomas Farm 19 UF 213777 Parahippus leonensis m3 2014 -12.45 2.47 Thomas Farm 19 UF 213777 Parahippus leonensis m3 2014 -11.69 1.6 Thomas Farm 19 UF 214560 Parahippus leonensis m1 2014 -12.92 0.78 Thomas Farm 19 UF 214560 Parahippus leonensis m1 2014 -12.41 2.12 Thomas Farm 19 UF 214590 Parahippus leonensis m1 2014 -12.73 1.83 Thomas Farm 19 UF 214590 Parahippus leonensis m1 2014 -10.42 0.45 Thomas Farm 19 UF 214867 Parahippus leonensis m2 2014 -11.96 0.2 Thomas Farm 19 UF 214867 Parahippus leonensis m2 2014 -11.72 1.28 Thomas Farm 19 UF 215280 Parahippus leonensis m3 2014 -10.88 0.73 Thomas Farm 19 UF 215280 Parahippus leonensis m3 2014 -10.22 0.08 Thomas Farm 19 UF 215289 Parahippus leonensis m2 2014 -12.22 0.6 Thomas Farm 19 UF 215289 Parahippus leonensis m2 2014 -10.42 0
54
Table A-1. Continued
Site Age (Ma)
Sample ID Taxon Sample Analyzed δ13C (V-PDB) ‰
δ18O (V-PDB) ‰
Thomas Farm 19 UF 215308 Parahippus leonensis m3 2014 -11.52 0.48 Thomas Farm 19 UF 215308 Parahippus leonensis m3 2014 -11.29 1.89 Thomas Farm 19 UF 215783 Parahippus leonensis m2 2014 -12.13 1.06 Thomas Farm 19 UF 215783 Parahippus leonensis m2 2014 -11.85 2 Thomas Farm 19 UF 216291 Parahippus leonensis m1 2014 -12.59 2.73 Thomas Farm 19 UF 216291 Parahippus leonensis m1 2014 -10.43 0.02 Thomas Farm 19 UF 257391 Parahippus leonensis m2 2014 -10.87 2.56 Thomas Farm 19 UF 257785 Parahippus leonensis m2 2014 -11.49 1.76 Thomas Farm 19 UF 258694 Parahippus leonensis M1 2014 -12.76 2.95 Thomas Farm 19 UF 258694 Parahippus leonensis M1 2014 -11.7 1.16 Thomas Farm 19 UF 258802 Parahippus leonensis m3 2014 -9.43 2.31 Thomas Farm 19 UF 259493 Parahippus leonensis m1 2014 -11.82 -2.12 Thomas Farm 19 UF 259493 Parahippus leonensis m1 2014 -13.73 1.78 Thomas Farm 19 UF 259495 Parahippus leonensis m1 2014 -13.85 1.69 Thomas Farm 19 UF 259495 Parahippus leonensis m1 2014 -12.51 0.16 Thomas Farm 19 UF 262997 Parahippus leonensis m3 2014 -9.51 0.98 Thomas Farm 19 UF 262997 Parahippus leonensis m3 2014 -11.23 1.29 Thomas Farm 19 UF 269846 Parahippus leonensis m1 2014 -12.36 0.51 Thomas Farm 19 UF 269846 Parahippus leonensis m1 2014 -11 1.4 Thomas Farm 19 UF 270907 Parahippus leonensis m2 2014 -12.62 0.14 Thomas Farm 19 UF 270907 Parahippus leonensis m2 2014 -10.78 1.77 Thomas Farm 19 UF 276773 Parahippus leonensis m3 2014 -11.4 1.24 Thomas Farm 19 UF 276773 Parahippus leonensis m3 2014 -10.82 2.27 Thomas Farm 19 UF/FGS 6427 Parahippus leonensis m3 2014 -10.85 0.58 Thomas Farm 19 UF/FGS 6427 Parahippus leonensis m3 2014 -11.27 0.48 Thomas Farm 19 UF/FGS 6441 Parahippus leonensis m1 2014 -11.92 0.82 Thomas Farm 19 UF/FGS 6441 Parahippus leonensis m1 2014 -10.99 1.57 Thomas Farm 19 UF/FGS 6749 Parahippus leonensis m1 2014 -12.54 1.59 Thomas Farm 19 UF/FGS 6479 Parahippus leonensis m1 2014 -11.46 1.12 Thomas Farm 19 UF/FGS 7171 Parahippus leonensis m3 2014 -11.8 2.13 Thomas Farm 19 UF/FGS 7171 Parahippus leonensis m3 2014 -11.46 1.15 Thomas Farm 19 UF/FGS 7172 Parahippus leonensis m3 2014 -11.83 1.65 Thomas Farm 19 UF/FGS 7172 Parahippus leonensis m3 2014 -11.52 0.58 Thomas Farm 19 UF/FGS 11004 Parahippus leonensis m2 2014 -12.43 1.8
55
Table A-1. Continued
Site Age (Ma)
Sample ID Taxon Sample Analyzed δ13C (V-PDB) ‰
δ18O (V-PDB) ‰
Thomas Farm 19 UF/FGS 11004 Parahippus leonensis m2 2014 -11.18 1.91
56
APPENDIX B VALIDITY OF LEGACY DATA
Stable isotope analysis is a valuable proxy for vertebrate paleontologists,
who use analysis of carbon and oxygen isotopes from fossilized bone and tooth
material to understand paleodiet (Wang et al., 1994), paleoecology (Macfadden
et al., 1999; Clementz and Koch, 2001; MacFadden and Higgins, 2004), and
paleoclimate (Bryant et al., 1994). Original data may come from first hand
analysis conducted with each new study, but researchers also rely on previously
published data to provide additional context for their interpretations. The Florida
Museum of Natural History (FLMNH) in Gainesville, Florida serves as the official
repository for fossils found in the state, and thus has amassed an extensive
collection of invertebrate and vertebrate fossil specimens which provide
researchers with a significant set of data available for isotope analysis. Florida
Miocene fossils are especially abundant, and have been collected from southern,
central, and northern localities throughout the state. While the studies focus on
the same type of material, they have been conducted by researchers of various
affiliations using varying methods in varying labs. Mass spectrometry in its initial
stages required skilled practitioners (Sharp, 2017) and even in the 1970s-80s,
when manufacturers began to produce mass spectrometers that could be
operated by a greater range of scientists, these processes left much room for
human error. While adherence to lab standards should correct for systematic
biases in the data it is worth revisiting this data to see if the legacy data can be
directly compared to data generated in modern scientific studies.
This supplemental study examined 10 out of 26 original stable oxygen and
carbon isotope data points from older publications using gas extraction
57
techniques on fossil teeth housed at the Florida Museum of Natural History. Not
all of the samples from the original publications are represented in this study for
two main reasons. First, some of the fossil teeth sampled in these two previous
studies had not yet been accessioned into the FLMNH vertebrate paleontology
collections, thus they had no associated FLMNH UF identification number and
could not be relocated. Efforts were made to track down these specimens, but
lack of documentation made it unclear if they eventually were accessioned into
the collection. Second, other fossil teeth were removed from the study because
they were unerupted or deciduous teeth. Previous studies (Bryant et al., 1996)
have shown that baby teeth carry the signal of the mothers milk, thus providing a
false signal of stable isotope interpretation. Using these filters, out of 16 samples
from MacFadden and Cerling (1996) and 10 samples from MacFadden (1998)
10 specimens were located and deemed viable for re-sampling.
Specimens sampled are from three early Miocene members of the
Perissodactyla (Table B-1).
Table B-1. Taxonomic representation of mammalian herbivores resampled from the late Miocene Love site in Florida.
Order Perissodactyla Family Equidae (horses, zebras) Cormohipparion (6) Family Rhinocerotidae (rhinoceroses) Aphelops (1) Teleoceras (4)
The two methods being compared in this study are individual-sample-gas
extraction techniques and automatic extraction using a Keil device. The samples
from both MacFadden and Cerling (1996) and MacFadden (1998) follow the
same methods of preparation and analysis. These samples were removed of
58
dentine or cement with a Dremel tool or dental drill, and the remaining enamel
was then pulverized using a mortar and pestle. The powdered enamel was then
treated with NaOCI, followed by acetic acid to remove organic surface
contaminants. Following this treatment, 50 mg of the sample was transferred to a
glass reaction vessel, where 5 ml of 100% H3PO4 added to the finger, then
evacuated using a glass carbonate extraction line for 1-2 hours in a vacuum at 5
X 10-5 T. The container was then placed in a 25°C temperature bath for half an
hour, after which the H3PO4 was mixed with the sample and left in the 25°C
temperature bath for forty eight hours. The CO2 resulting from this reaction was
analyzed in the University of Utah Department of Biology Finnigan mass
spectrometer, whose analytical precision is reported as being within 0.2%. The
new samples were analyzed using an updated treatment of H2O2 and acetic acid
to remove organic surface contaminants, then analyzed in the University of
Florida in finnigan mass spectrometer coupled with a Kiel III carbonate
preparation device.
The offset between the data run using gas extraction techniques at the
University of Utah in the 1990s and the data run using automatic extraction
techniques at the University of Florida ranged from .05 ‰ to 2.54 ‰ (Table B-2).
Most of the offset shifted towards more positive δ13C and δ18O values, but two
points shifted toward more negative δ13C and δ18O values.
59
Figure B-1. Original δ13C data (blue) compared with new δ13C data (red).
Results from a Kruskal-Wallis rank sum test qualify that the difference
between the two data points is statistically significant, and thus the older data
points can be confidently used moving forward.
Table B-2 Results of Kruskal-Wallis rank sum test on the δ18O data from all sites under study.
chi-squared degrees of freedom
p value
Kruskal-Wallis 9 6 0.4373
60
Figure B-2. Original δ18O data (blue) compared with new δ18O data (red).
Results from a Kruskal-Wallis rank sum test qualify that the difference
between the two data points is statistically significant, and thus the older data
points can be confidently used moving forward.
Table B-3. Results of Kruskal-Wallis rank sum test on the δ18O data from all sites under study.
chi-squared degrees of freedom
p value
Kruskal-Wallis 7.6364 8 0.4698
61
APPENDIX C DIGITIZATION
Overview of vouchered museum specimens to which isotope data was added. This includes specimens from the following publications: Macfadden et al., 1999; MacFadden, 2005; Yann and DeSantis, 2014; Secord et al., 2012; Feranec and MacFadden, 2006; Zanazzi et al., 2007; MacFadden and Cerling, 1996; Whiting et al., 2016; Feranec, 2002; MacFadden, 1998; Koch, 1998; Hoffman, 2006. Table C-1. Vouchered museum specimens to which isotope data was added.
UFID Taxon Specimen Publication
221407 cf. Acritohippus isonesus P3 or P4, right upper partial Hoffman, 2006
221415 Merychippus primus P3, right upper Hoffman, 2006
221419 Merychippus primus P4, left upper Hoffman, 2006
26162 Tapirus webbi maxilla, with left P3-M3 MacFadden and Cerling, 1996
55824 Pseudhipparion simpsoni m2, right upper MacFadden and Cerling, 1996
115776 cf. Tapirus veroensis mandible, left partial with p3, m1-m3 MacFadden and Cerling, 1996
13814 Negaprion sp. tooth, lower MacFadden and Cerling, 1996
13885 Carcharhinus sp. tooth, upper MacFadden and Cerling, 1996
17730 Equus sp. molar, lower Koch, 1998
59606 Teleoceras proterum P3, right upper MacFadden, 1998
59775 Aphelops malacorhinus p3 or p4, left lower, partial MacFadden, 1998
59776 Aphelops malacorhinus p3, right lower, partial MacFadden, 1998
202890 Aphelops malacorhinus M3, right upper MacFadden, 1998
403159 Teleoceras proterum M3, left upper MacFadden, 1998
403160 Teleoceras proterum M3, left upper MacFadden, 1998
17730 Equus sp. M3, right upper MacFadden et al., 1999
17731 Mixotoxodon larensis incisor, left upper MacFadden, 2005
17734 Mixotoxodon larensis cheektooth, left upper MacFadden, 2005
162371 Toxodon sp. P2 or P3, left upper MacFadden, 2005
162373 Toxodon sp. tooth, partial MacFadden, 2005
Table C-1. Vouchered museum specimens to which isotope data was added.
62
UFID UFID UFID UFID
162378 Toxodon sp. tooth, partial MacFadden, 2005
162380 Toxodon sp. tooth, partial MacFadden, 2005
202890 Aphelops malacorhinus M3, right upper Feranec and MacFadden, 2006
403151 Tapirus webbi p2, left lower, partial Feranec and MacFadden, 2006
403159 Teleoceras proterum M3, left upper Feranec and MacFadden, 2006
403160 Teleoceras proterum M3, left upper Feranec and MacFadden, 2006
209563 Mesohippine grade equids dentary, right partial with p3-m3 Zanazzi et al., 2007
206864 Hemiauchenia macrocephala p4, left lower Feranec, 2012
249223 Ectocion osbornianus dentary, left with m2 Secord et al., 2012
249297 Ectocion osbornianus m3, right lower Secord et al., 2012
249331 Ectocion osbornianus m2, left lower Secord et al., 2012
249376 cf. Ectocion osbornianus Molar, upper partial Secord et al., 2012
249379 cf. Ectocion P4, left upper Secord et al., 2012
249816 Ectocion parvus M2, right upper Secord et al., 2012
249817 Copecion davisi M2, left upper Secord et al., 2012
249819 Copecion davisi M1, right upper Secord et al., 2012
249854 Hyracotherium sandrae m3, right lower Secord et al., 2012
249856 Ectocion parvus p3, right lower Secord et al., 2012
249858 Ectocion parvus m1, left lower Secord et al., 2012
249859 Copecion davisi m1, right lower Secord et al., 2012
250169 Ectocion osbornianus m2, left lower Secord et al., 2012
250208 Hyracotherium sandrae maxilla, right with M3 Secord et al., 2012
250211 Hyracotherium sandrae M3, left upper Secord et al., 2012
250825 Ectocion osbornianus p3, left lower Secord et al., 2012
250876 Ectocion osbornianus M2, right upper Secord et al., 2012
250890 Ectocion osbornianus dentary, left with m3 Secord et al., 2012
250965 Ectocion osbornianus dentary, left with m2-m3 Secord et al., 2012
251619 Copecion davisi p4, left lower Secord et al., 2012
Table C-1. Vouchered museum specimens to which isotope data was added.
63
UFID UFID UFID UFID
252156 Hyracotherium sandrae M3, left upper Secord et al., 2012
252501 Coryphodon eocaenus tooth, partial Secord et al., 2012
252519 Copecion davisi m2, right lower Secord et al., 2012
252541 Copecion davisi dentary, right with m1-m2 Secord et al., 2012
252672 Coryphodon sp. tooth, enamel fragment Secord et al., 2012
253628 Ectocion sp. m1, right lower partial Secord et al., 2012
253630 Ectocion osbornianus P4, left upper Secord et al., 2012
7559 Bison latifrons partial associated skeleton Yann and DeSantis, 2014
27546 Equus sp. P4, right upper Yann and DeSantis, 2014
259941 Bison latifrons p3, left lower Yann and DeSantis, 2014
259942 Bison latifrons p3, left lower Yann and DeSantis, 2014
33419 Equus sp. P4, left upper Yann and DeSantis, 2014
33421 Equus sp. p4, right lower Yann and DeSantis, 2014
272289 Alligator olseni tooth Whiting et al., 2016
289279 Alligator mississippiensis tooth Whiting et al., 2016
64
APPENDIX D WOMENS STUDIES: THE FEMMES OF STEM
Summary
In addition to my paleontology research for a Master of Science degree, I spent
two semesters developing an independent, multidisciplinary web based project as
partial fulfillment for a certificate in women’s studies from the University of Florida. The
purpose of the project, entitled the Femmes of STEM.
(https://www.femmesofstem.com/), is to use feminist science studies as a basis for
research into the history of women in STEM fields (science, technology, engineering,
mathematics). The results are shared with a general audience online via blog posts,
podcast episodes, and development of an open access online database of women in
the history of science.
Introduction
The history of science all too often is presented as a history without people of
color, women, or nonwestern knowledge. While there is discourse regarding the status
of women and minorities in STEM today in academia and between STEM academics
(National Sciecne Foundation, 2017; Wyer et al., 2013), there is less conversation about
the place of women and minorities in STEM history. Historical women scientists are
presented as outliers, if at all, and historical scientists of color are often completely left
out of the picture. Thus, the history of science is presented as an accomplishment of
white, western men. Clearly, this is not the case, but finding the stories of women as
scientists is difficult, and this feeds the narrative that women either do not belong in the
sciences or are not even capable of being scientists.
65
From personal experience, many scientists and citizens alike assume that this is
simply because Women and people of color were not a part of science history. These
casually sexist, racist attitudes assume women and people of color are newcomers to a
field which was built upon the labor of white, western, males. Science texts used in
classrooms and pop culture depictions of scientists only serve to reinforce these ideas,
as they present the history of science through a white, western, male perspective. The
lack of histories of women in stem perpetuate the idea that women are newcomers to
science - outsiders, who have not contributed to our knowledge, and may not be
capable of succeeding in the field.
The purpose of the research and its development in podcast form is to refute
these ideas by presenting the history of women, especially women of color and non
western women, in science. The questions to be addressed are:
• What are the stories of women in stem history?
• Why have we not seen these stories before?
Background
Perceptions of Scientists
Studies show that when people envision a scientist, they call to mind the image
of a middle aged, white male (Mead and Metraux, 1957; Basalla, 1976). Such
perceptions are shown to have been formed as early as the end of a student's
elementary education (Entwisle and Greenberger, 1972) and continues on to inform
adult’s bias about scientists, including their own place - or lack thereof - in the world of
science (Nosek et al., 2002).
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Perceptions like these lead to the association of science as a masculine, white
field, and inform both public and private attitudes towards who can succeed in science.
Arguments against women’s entry to science range from the proposition that women's
nature is incompatible to science to the idea that women's nature allows them to be
successful in only certain types of science.
History of Women in Science and Feminist Science Studies
Modern feminist critique of science began in the 1970s and 80s (Schiebinger,
1997, 2004) and is being addressed by scientists as well as scholars in women's
studies, philosophy of science, and history of science. In a review essay regarding the
study of women in the history of science, Schiebinger (1987) outlines four conceptual
approaches to feminist science studies:
• recover the work of early women scientists who have been overlooked by historians
• to analyze the limits of women's access to science
• to study how science has characterized/defined women
• to study the masculinity of science Interestingly, these approaches can be seen as having differing views of women
in science, from trying to prove simply that women are capable of doing science, to the
idea that the lack of women in science is due to barriers to entry, to the idea that neither
case is as important as the fact that science itself needs an overhaul (Schiebinger,
1987).
Feminist science studies examine not only the history of women in science fields,
but also provides a critical analysis of how gender, sexism, and racism play a part
science studies (Harding, 1986, 1998, 2006). Science is presented as a pure form of
knowledge, above the influence of human bias, and thus believe there is no way that
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sexism, racism, or prejudice has played a part in science (Harding, 1986). It only takes
a short look into our history, and even our present, to see this is not the case: eugenics
has been taught as science at the university level (Bashford and Levine, 2010), gender
has been presented as a binary despite our understanding of biology (Kitzinger, 1999),
and current studies fail to take into account the presence and knowledge of native
people (Dussel, 1997; Smith, 2012). Women's studies is one of many fields that
encourages a critical look at scientific structures and the people who play a part in them,
including issues like:
• Who is Viewed as a Scientist
• Research Priorities
• Study Populations
• Scientific Language
• What is Considered "Science"? Feminist science studies encourage analysis how choices are being made about
what to research and what research to fund, who is in the position of power to make
these decisions, and who benefits from these decisions. Do the groups correlate? Do
populations used in experiments (mice in clinical trials, for example) accurately reflect
the population who stands to benefit? (Often not) How is scientific language gendered,
and what effect does it have on scientists and scientific research? How do patriarchal
structures and colonialist views inform what we consider “science” versus “indigenous
knowledge,” “women’s work,” etc?
Research
Literature pertinent to understanding the context around perspectives on women as
scientists, history of science, and science studies are available, but the literature falls
short is on describing or analyzing the lives of individual scientists. Research into the
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lives of scientists who have not yet been written about will require access to archives
with periodicals, government documents, photographic images, and interviews. In cases
possible, new interviews are being recorded with available sources for this project.
While some STEM researchers write about feminist and postcolonial approaches to
science (Walker, 2014; Whitten, 2012) the majority of these studies come from non-
STEM fields, such as philosophy, sociology, and women's studies (Dussel, 1997;
Wilson, 2001; Harding, 2006). Many, if not most, scientists are not introduced to feminist
or postcolonial issues, and have not been given reason to believe that either issues of
gender or colonialism affect science (Harding, 2006). As a researcher initially trained in
the natural sciences, it was unfamiliar to me to use social science methodologies to
analyze STEM, but as a woman, especially as a woman of color in this field, the
importance of and need for this discussion is clear.
Thus, while the project is meant for a general audience, it is most crucial to place before
an audience of scientists. This requires explanations of feminist theory, postcolonial
theory, feminist science studies, and so forth to be presented to a set of listeners mostly
untrained in the humanities and unfamiliar with these theories or their
importance/relation to science. The discourse between humanities and science is often
nonexistent, but this project serves as one bridge in the gap.
Product And Press
The overall goal of the Femmes of STEM project is twofold. First, to rethink the narrative
of women - or the apparent lack of women - in science. Second, to use historical
women's success and struggles as a way to call attention to and discuss feminist issues
in STEM today.
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Over the year since the projects launch, the amount of research undertaken has
surpassed the capacity of a biweekly show, and what began as a podcast is now
expanding into a growing website which features reference lists, biographies, open
access resources, and guest posts from fellow contributors thinking about the
intersection of feminism, history, and science.
The Femmes of STEM blog publishes weekly on Mondays and Wednesdays, with
Monday posts alternating between four series: the Resource Round Up, Social Media
Scientists, Reading Recommendations, and Listening Recommendations. Wednesday
posts are written by guests, typically women in STEM, and highlight women in science
history.
Since January, a preliminary reference list of historical women in science and historical
women of color in science has been made public on the website, but a two new, in
depth, searchable databases will be officially launching this July.
The first is an expanded version of the historical women in science database, with over
900 unique entries of women from science history, spanning the 20th century to the
23rd century BCE. Fields of study include archeology, astronomy, biology, chemistry,
earth science, engineering, invention, mathematics, medicine, natural philosophy,
physics, and technology. Women are represented from Asia, Australia, Europe, North
America, and South America.
The second is a database showing notable events in science history which involve
women in STEM. Events include issues of patents by women inventors, award dates,
and birth/death dates. Currently, there is at least one event per calendar day, but this
will be supplemented with birth/death dates from the historical women database above.
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The beta pages for each page are available via the following links: Historical Women in
STEM database (https://www.femmesofstem.com/database), On This Day database
(https://www.femmesofstem.com/onthisday). Press for the project can be found at
https://www.femmesofstem.com/press/.
Our current social media reach is as follows:
• Facebook (600+)
• Instagram (1.2k+)
• Twitter (2.7k+) Mentorship
Over the past two semesters I mentored two undergraduate biology students who
worked as interns for the Femmes of STEM project. During the first semester, one
student focused primarily on research while the other focused on our social media and
publicity. During the second semester, they each added on primary responsibility for a
database, with the goal of having the database in beta mode by the end of Spring 2018.
As undergrads, the students did not yet have experience using university research
resources, citation managers, and other organizational tools, so our focus the first
semester was reviewing research basics, while our focus the second semester was
research reporting through personal publication online and academic submissions.
Conclusion
The Femmes of STEM project was created to combat this false narrative and show that
women and minorities are not newcomers to the world of science, technology,
engineering, and mathematics (STEM) by presenting research that shows we have
always been a part of the past - the problem is that simply that we have not always
been a part of history. Research in the fields of women's studies, the philosophy of
science, science and technology studies, and the history of science have made some
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headway into these issues, but most remains trapped behind paywalls and generally
inaccessible to the public. The Femmes of STEM pairs this research with popular
science writings, primary sources, and personal narratives to produce an accessible
project that shares the history of women in STEM fields one story at a time
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BIOGRAPHICAL SKETCH
Michelle Barboza was born in 1993 in Los Angeles County, CA. She is a first
generation Mexican American, and the oldest of two girls. She graduated from Ramona
Convent Secondary School in Alhambra, California with honors, and began her
undergraduate career at California State University Fullerton with honors upon entrance
in 2011. Michelle graduated with a minor in Geography and a major in Geological
Sciences in 2016. The same year, Michelle began her graduate studies at the University
of Florida and published her undergraduate thesis “The age of the Oso Member,
Capistrano Formation, and a review of fossil crocodylians from California.” While in
graduate school, Michelle also began a project dedicated to the history of women in the
fields of science, technology, engineering, and mathematics. Upon graduation, Michelle
will move back to the West Coast to marry her partner of five years.