QUANTIFICATION OF WEAR IN EQUUS TEETH FROM FLORIDA CHRISTIAN OWENS GEORGE

Transcription

1 QUANTIFICATION OF WEAR IN EQUUS TEETH FROM FLORIDA By CHRISTIAN OWENS GEORGE 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 2002

2 Copyright 2002 by Christian Owens George

3 ACKNOWLEDGMENTS There are several people I wish to thank for their help and support on this project. First, I thank my advisor, David Webb, and my committee members for their patience and suggestions. I thank Alex Nouri for help in verifying and making the bevel measurements. I also thank Dorcas Brown and David Anthony for all the questions I had about bit wear. Finally, I would like to thank my parents for their constant encouragement. iii

4 TABLE OF CONTENTS page ACKNOWLEDGMENTS... iii ABSTRACT... vi CHAPTER 1 INTRODUCTION NATURAL WEAR PATTERNS IN HORSE TEETH...3 Introduction... 3 Materials and Methods... 6 Sample of Horse Teeth from Leisey Shell Pit... 6 General Taphonomy... 6 GIS... 7 Results Taphonomic Wear Ontogenetic Wear GIS Discussion General Wear GIS Quantification BIT WEAR IN WILD HORSES...22 Introduction Previous Bit Wear Studies Materials and Methods Sample of Equus for this study Bevel Measurements Bevel Measurements Results Statistical Tests of Bevel Measurements Comparison of Beveling Hooks Discussion Beveling Effect of Ontogenetic and Taphonomic Wear on Beveling iv

5 4 CONCLUSIONS...36 APPENDIX GENERAL TEETH MEASUREMENTS...37 LIST OF REFERENCES...38 BIOGRAPHICAL SKETCH...40 v

6 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 QUANTIFICATION OF WEAR IN EQUUS TEETH FROM FLORIDA By Christian Owens George August 2002 Chair: S. David Webb Major Department: Department of Geological Sciences This thesis represents an investigation into three types of wear found in horse teeth. This sample comes from two species of Pleistocene Equus from Leisey Shell Pit, Hillsborough County, Florida. The two natural types of wear are ontogenetic wear and taphonomic wear. A third type of wear, not expected in this sample, is bit wear. A general description of the wear in the teeth was made. Secondly, a new method of quantifying wear has been developed using GIS. GIS is able to quantitatively show differences in wear. The second section is a study to determine if any natural wear can mimic bit wear. This population of horses does not show wear similar to bit wear in domestic horses. vi

7 CHAPTER 1 INTRODUCTION Horse teeth have been well studied in terms of dietary or microwear (Fortelius and Solounias, 2000). However, microwear studies are generally limited to dealing with the last meals of an animals life, rather than with the accumulation of tooth wear through an animal s life. After death, taphonomic wear takes place, but teeth are generally ignored in taphonomic studies. This is because teeth are generally poor taphonomic indicators. They are relatively robust and tend to survive most taphonomic processes, and so tend to show little taphonomic wear compared to other bones. In addition, they cannot be used as paleocurrent indicators and will not be gnawed like long bones (Voorhies, 1969; Behrensmeyer and Hill, 1980; Behrensmeyer and Kidwell, 1985; Badgley, 1986; Lyman, 1994). A third type of wear found in horse teeth is human induced. Bit wear is found in domesticated horses and is caused by the impact of the bit on the anterior edge of the lower second premolar (Brown and Anthony, 1998; Anthony and Brown, 2000). This type of wear has been used to determine whether horses found in archeological sites were domesticated. However, this claim has been disputed (Levine, 1999). An assessment of the overall wear in horse teeth is necessary to determine whether any natural process can mimic bit wear. 1

8 2 Since previous inquiries into tooth wear have tended to examine either ontogenetic or taphonomic wear, there exists the need to deal with the complete wear that a tooth has experienced. The goal of this paper is to describe the wear overall wear in a select sample of Pleistocene horse teeth from Florida. Secondarily, this study will serve as a control study on a third kind of wear, not expected in this early Pleistocene sample, namely bit wear found in modern and early domesticated horses. In the broadest sense, this will be an analysis of the wear phenomena in a natural assemblage of horse teeth. Measuring wear at all mature ages and through a variety of well studied taphonomic processes will provide a comprehensive analysis of the natural wear process. This study will substantially broaden the basis by which archeologists and paleontologists interpret wear in horse teeth. Additionally, it will show that no natural process can mimic bit wear. Another need is a method to further quantify wear. A GIS (geographic information systems) technique has been developed to quantify the wear on the occlusal surface of the teeth. GIS is a tool used to display spatial data. Instead of dealing with large-scale geographic problems, GIS has been adapted to a tooth. The second purpose of this study is to determine if any natural process can mimic bit wear. The GIS technique will be used as part of this analysis. A statistical analysis will also be used to determine if these teeth show similar beveling to domesticated horses.

9 CHAPTER 2 NATURAL WEAR PATTERNS IN HORSE TEETH Introduction Taphonomic studies tend to concentrate on postcranial elements because these provide the best answers to the kind of questions asked by taphonomy. Taphonomists characterize the history of accumulation of a fossil assemblage. Typically such studies describe the number of individuals and species present, the age profiles of populations, the frequencies of elements represented, the spatial arrangement of bones and the type of modification the bones have undergone (Behrensmeyer and Hill, 1980; Behrensmeyer and Kidwell, 1985; Badgley, 1986; Pratt and Hulbert, 1995). In most cases, teeth are the densest and most easily preserved part of a vertebrate skeleton. Therefore, their presence in an accumulation of bones is typically expected. Their resistance to wear also prevents them from recording the breakage, cracking and abrasion that is useful in determining the conditions in which a site was preserved (Behrensmeyer, 1978). The typically cubic shape of teeth also prevents them from being used as a paleocurrent indicator, or to be transported great distances (Voorhies, 1969). Finally, teeth have little or no food utility, so they generally do not record modification by carnivores or humans (Lyman, 1994). Microwear studies constitute another related subject that has matured considerably in the past two decades. The goal of microwear analysis is to reconstruct the diets of animals by looking at the microscopic abrasion on teeth from the food that was eaten 3

10 4 (Fortelius and Solounias, 2000). These studies look at what might represent as little as the last meal of the animal. These studies are limited by the technique and cannot describe the overall pattern of wear that has developed over the course of an animal s life. The present study investigates all aspects of tooth wear both during life and after death. If features a large, population of two Equus species from an early Pleistocene coastal site in Florida previously studied by Hulbert (1995). The goal of this study is a quantification of all aspects of wear that has affected these teeth. This study examines two species of Equus from Leisey Shell Pit 1A. Leisey Shell Pit is a commercial quarry on the south side of Tampa Bay. The shell beds in this area are quarried and crushed for roadbed material. Within the exposed section of molluskrich sediment is a persistent dark bed that contains high concentrations of terrestrial vertebrate remains. This area was excavated by the FLMNH in the spring of 1984 and over 50,000 catalogued specimens were collected. This site has been dated to approximately 1.5 Ma by a variety of methods (Jones, 1995; MacFadden, 1995). Molluscan and vertebrate biochronology, paleomagnetic analysis and strontium isotope geochronology all indicate a similar age (Morgan and Hulbert, 1995). Some of the most common fossils collected at Leisey shell pit are horses. From the well-preserved remains, Hulbert (1995) was able to recognize two distinct species. However, due to the current degree of uncertainty among paleontologists as to the valid species of Equus of North America, these two populations were not assigned to a specific species (Azzaroli, 1995). Equus sp. A is similar to E. scotti and E. conversidens, but is intermediate between them in size. Equus sp. B is more similar to the modern Asses or hemiones, Asinus sp. (Hulbert, 1995), and probably represents a new species.

11 5 A taphonomic study of the terrestrial mammal remains from Leisey has also been published (Pratt and Hulbert, 1995). This study looked at the articulation and association of elements, bone orientation, bone modification, bone completeness, weathering and surface erosion of the bones and the relative representation of bones. This study dealt primarily with the taphonomy of post-cranial elements. The authors identified several important taphonomic agents. The fossils were deposited in a shallow marine or estuarine environment. They experienced some water wear and chemical staining. They also noted carnivore modification on a small number of the sample. A third type of wear was caused by trampling. In the present quantitative study of wear on horse teeth, water wear and trampling will be the most important taphonomic agents to evaluate. The goal of this paper is to comprehensively quantify all aspects of tooth wear. The effects of wear on Leisey horse teeth can be partitioned into those effects accrued during ontogenetic wear, and postdepositional effects including water wear, transport, and trampling. GIS will be used to predict the type of wear that has most strongly affected these teeth. Isolated teeth should show a quantitative difference between taphonomic and ontogenetic wear. While the p2s are present in the mandible, they are protected along the distal edge by the p3s. Isolated teeth should show a relatively even pattern of taphonomic wear around the tooth since they are no longer part of a tooth row. Overall, this study should provide useful information to two areas. First, the quantification of wear will improve the understanding of taphonomic effects on teeth. This may help improve microwear studies, by first looking at the overall ontogenetic wear of the teeth and second by separating it from the effect of taphonomy on the teeth.

12 6 Materials and Methods Sample of Horse Teeth from Leisey Shell Pit The focus in this study will be on individual teeth, the lower second premolars (p2s). The main reason for this is that the major impact of grass and other food introduced into the oral cavity and manipulated by the tongue falls upon the anterior (front) edge of the second premolar. It is also uniquely identifiable, whereas the intermediate premolars and molars can rarely be assigned their exact position once they become isolated. The sample size is 62 p2s in mandibles and 52 isolated lower premolars. This is the total number of teeth studied. Each tooth could not be used for every analysis, so sample size varies. General Taphonomy The first step in this study was to provide a general description of the overall wear on each tooth. The overall wear on the teeth addresses the effects of water wear, transport, trampling and any other postdepositional effects on the teeth. The other aspect of the overall wear was to assess the ontogenetic wear. I looked at the macroscopic wear during life. This is opposed to microwear that was not studied. Diet was not in question here. The next step was to take various measurements of the teeth. I measured the crown height, length and width of the p2s was measured as well as the paraconid cusp length, cusp width. This was to determine what kind of macroscopic wear has affected the teeth. Measurements also provided information about the relative age of the horse. The importance of estimating the age of the teeth is that age-related wear represents the

13 7 effects of wear during life, in contrast with taphonomic effects that occur after death and therefore are not age related. Since horse teeth grow continuously until their roots close, and then continue to emerge through their entire life, the crown height of any tooth provides a good indicator of age. Such wear stages in Equus fossil teeth can be assumed to correspond to absolute year classes in living species (Hulbert, 1984). GIS The first step to quantify the teeth in GIS is to capture the teeth as a digital image. This was done by scanning the occlusal surface of the teeth with a standard flat bed scanner. They were scanned at a high enough resolution to provide enough clarity while still maintaining workable file sizes. After much experimentation, four times the actual size, proved a practical scale for these results. The teeth were scanned with a scale to provide reference within the image (Figure 1). The scale was fixed to the scanner. All teeth were then placed with the lingual side of the tooth along the vertical axis and the distal end along the horizontal axis. In this manner, the point where the entoconid meets the hypoconulid functions as the origin of the tooth. The primary concern was to have the origin identical on all teeth. Given the variability in teeth this meant that sometimes the lingual or distal side would not completely align with the axis (Figure 2).

14 8 Figure 1: Scanned images of a left p2 (scale in cm) Figure 2: Right p2 (scale in cm)

15 9 Having a standard origin was the primary concern so that the images could be rectified. Rectification is the process by which satellite images or aerial photographs are given coordinates and put into the real world. There was less concern with the differences in size and shape of the teeth. The reference scale on the scanned images provided the frame of reference to rectify the images. Four points are needed to determine the geographic position of an image, but adding more points will give greater accuracy. Typically, seven points were selected on the image and then assigned a coordinate based on the scanned scale. The scale is in centimeters and the small hashes are millimeters. As defined above, the origin is at the vertex of the scales. The tooth is always in positive space. In the case of the left p2, positive is to the right on the horizontal axis. A point lying on the horizontal scale at the first cm mark would be defined as (1, 0) in cm. The scanned image then provided a reference for the digital data. The next step was to bring the image into a GIS software package (ESRI s ArcView was used) so that the areas of wear could be digitized. For each tooth, ontogenetic wear and postontogenetic wear were digitized onto the image. The actual teeth were still looked at to maintain the highest accuracy. The digitizing involved locating the areas of wear on the teeth. Lines and polygons were digitized onto the teeth to match the shape of wear. Once the digitizing was complete, the wear for each tooth could be shown, as well as the total wear of the entire sample. The next step was to try to quantify the wear. The vertices of all the polygons were exported out of ArcView using the program Global Mapper. This produced a list of x and y coordinates for taphonomic and ontogenetic wear in both left and right teeth. From this data the mean center of each

16 10 polygon was calculated. This is essentially the average of all the points that make up a polygon. Then the mean center of all the damage for each kind of wear on the left and right teeth was calculated. To determine the error in the mean center, the standard distance was calculated. This is equivalent to the standard deviation. To test the hypothesis that there should be a difference in location between ontogenetic and taphonomic wear the average distance between the mean center of each polygon and the mean center of the total wear for both ontogenetic and taphonomic wear was calculated. A weighted average was taken to determine if wear was more common on a particular side. Descriptive statistics and a t- test were performed on each of the data sets to determine the significance of the results. Results Taphonomic Wear The following observations on the large sample of isolated teeth are divided into three sections. These consist of taphonomic (or postmortem) wear, ontogenetic (or masticatory) wear, and GIS mapping of the above features. The first observations of wear were a qualitative assessment of taphonomy. These were based on the major types of wear. The first of these was cracks in the enamel. Small cracks are probably related to subaerial exposure. They resemble cracks in bone due to drying (Figure 3). These were found on almost every tooth in varying degrees. They were digitized in GIS when they were found on the occlusal surface.

17 11 Figure 3 Cracks A common feature is cracking in the enamel. Both large and small cracks were found. The large cracks and breaks are probably the result trampling or other crushing damage (Figure 4). Figure 4 Breaks in the enamel

18 12 The five wear classes were based on the degree of wear (Figure 5). Category 1 showed the least wear. These teeth had intact roots and there were no chips or large cracks in the enamel. Category 2 had small chips and cracks. If the tooth had larger chips and cracks and broken roots it was assigned to Category 3. Category 4 teeth had large breaks and damaged roots. The teeth with extreme wear were placed in Category 5. These teeth had breaks through the entire tooth. Figure 5 Wear Stages The 48 isolated were then assigned to a wear category. There was a bimodal distribution of wear (Table 1). Most of the teeth showed slight wear and next category was extreme wear. Table 1 Wear Stages Category Number Total 48

19 13 A similar pattern of wear was found in the roots of the teeth (Table 2). In this case, the most common type of wear was either slight breakage of the roots, or complete loss. This wear pattern is more significant since it assuredly caused by taphonomic effects on the teeth. Table 2 Root Wear Wear Stage Number Total 48 Other observations were made on the teeth. The relative amount of polish was also recorded (Table 3). The polish is fine scratches presumed to be caused by water wear. The majority of the teeth show polish, which is to be expected (Figure 3). Table 3 Degree of Polishing Degree of polish Number Percentage of total No polish Some polish 6 14 Complete polish Figure 6 Polish

20 14 These were found in a shallow marine setting so it is not surprising that they show water wear. The teeth were not completely submerged for long periods. There is no obvious rounding so the teeth did not travel a great distance nor were impacted for a long period. Ontogenetic Wear I first observed that there seems to be a majority of wear on the front edge of the teeth. Another observation is the saddle that develops due to ontogenetic wear (Figure 7). It develops between the metastylid and the metaconid because of wear with the upper P2. The saddle appears to be most common on younger teeth, though it was found on wellworn, mature teeth. 33.3% of the teeth show this type of wear (Appendix A) Figure 7 Saddle wear GIS The results of the GIS project show two distinct wear patterns for ontogenetic and taphonomic wear. Ontogenetic wear tends to be concentrated on the anterior and central part of the tooth (Figure 8). The taphonomic wear is generally spread around the

21 15 perimeter of the tooth, with a slightly more common occurrence on the front edge or prow of the tooth (Figure 9). Figure 8 Ontogenetic wear of a left and right p2. Figure 9 Taphonomic wear of a left and right p2. The pattern also is very similar between left (Figs. 8 and 9) and right (Figs. 8 and 9) teeth. The differences are mainly due to the greater number of right teeth. The lefts also showed a few examples of very large amounts of damage. These areas correspond to large breaks in the teeth. The majority of taphonomic wear was small chips and breaks in the enamel. Another type of taphonomic wear recorded was cracks in the dentine and enamel (Figure 10). This type of wear was the least common found on the occlusal surface.

22 16 Figure 10 Cracks on left and right p2s. However, it was found much more frequently on the teeth overall. Since this analysis of wear was limited to just the occlusal surface this wear might not represent the overall wear of the teeth. There are teeth that may be badly broken, but their occlusal surface remains relatively undamaged. The above has been a qualitative description of the GIS results. Here are the quantitative results of the GIS analysis (Tables 5, 6 and 7). Figures 11 and 12 show the location of the centers of wear for each area of damage.

23 17 Right Centers of Wear Length (cm) Width (cm) Right taphonomic wear Mean center taphonomic wear Right life wear Mean center life wear Figure 11 Right centers of wear

24 18 Left Wear Centers Length (cm) Left life wear Mean Center life wear Left taphonomic wear Mean Center taphonomic wear Width (cm) Figure 12 Left centers of wear Table 5 t-test of Distance from Mean Center 1 Right A wear Right B wear Left A Left B Mean Variance Observations Hypothesized Mean Difference 0 0 Df t Stat t Critical one-tail A wear refers to taphonomic wear. B wear refers to ontogentic wear.

25 19 Table 6 Left Distance Statistics B dist x B dist y A dist x A dist y Mean Median Standard Deviation Sample Variance Range Minimum Table 7:Right Distance Statistics B dist x B dist y A dist x A dist y General Wear Mean Median Standard Deviation Range Minimum Maximum Discussion The overall taphonomic wear of these teeth tends toward a bimodal distribution (Table 1). Light wear and extreme wear represent most of the wear found on these teeth. All of the teeth are coming from a similar environment. It is expected that the teeth will show some wear, and this is represented by the large number of teeth in category two. Presumably, very few teeth should be unworn, and this is shown by the small numbers of category one. Category five tends to be large because this is the final wear category. Once a tooth has been worn into this category, any additional wear will not change the category.

26 20 The distribution of the teeth into the wear categories may have more to do with the definition of wear categories rather than any actual characteristic of the wear. Though I feel these categories represent natural groupings of wear conditions, other categories could be defined that would change the distribution of teeth. A quantitative description of wear is needed. GIS Quantification Isolated teeth in a natural environment should have equal wear on all parts of the teeth. Qualitatively there is a difference between ontogenetic wear and taphonomic wear. Ontogenetic wear seems to be more centered and concentrated towards the anterior end. Taphonomic wear seems to be evenly distributed around the outside of edge of the tooth. Taking the results of the spatial analysis a t-test was run to determine if there was a statistically significant difference between the centers of ontogenetic and taphonomic wear (Table 6). For the left teeth, the test showed that there was no difference in distribution. This is probably the function of a small sample size. The right teeth do show a significant difference between ontogenetic and taphonomic wear. The larger difference in average distance from the mean shows that the taphonomic wear tends towards the outside of the teeth and the ontogenetic wear is more concentrated to the centers. There seems to be no differences in wear between sides (Table 7). Given the large standard deviations of these values, and the very small means there probably isn t any variation. This means that wear has affected these teeth equally in all dimensions. This supports the original hypothesis. Another factor to consider is the variation in teeth size. This was not compensated for in this analysis. The teeth range in width by 3.41 mm and length by 9.25 mm

27 21 (Appendix A). The standard deviation of the distances is about 1 cm (Table 7) for all the values. Since the standard deviation is almost equal to the maximum range in the length and almost 3 times that of the width, I feel that the size differences can be ignored. Though there may be some problem with the scaling effects due to size differences. For the difference in the distance of wear from the mean center, the size range should affect both ontogenetic and taphonomic wear equally. I am not comparing the wear between sets of teeth, just between ontogenetic and taphonomy. Therefore, any error will be equal between both types of wear. The objective of this study, to find a quantitative way to describe wear, was met. GIS provides a way to both graphically present data and perform statistical tests on data. Though this study was limited to one surface of the teeth, I feel that it could be expanded in include other areas of taphonomy and paleontology.

28 CHAPTER 3 BIT WEAR IN WILD HORSES Introduction Previous Bit Wear Studies Dorcas Brown and David Anthony in a series of papers (Brown and Anthony, 1998 and Anthony and Brown, 2000) have defined bit wear and used it as evidence for the earliest domestication of the horse. In a properly bitted horse, the bit rests on the horse s tongue between the incisors and the premolars. When the reins are pulled, the bit presses into the soft tissue of the mandible and causes the horse to turn its head or tuck its chin. To relieve pressure, the horse will lift the bit with its tongue and bite it with the anterior end of the second premolars (P2s), especially the lower premolars (p2 s). The horse s cheeks prevent the bit from being moved any further back in the mouth. As the bit is lifted onto the p2s by the horse s tongue it produces frequent impacts on a very small area. This causes both microscopic and macroscopic wear of the teeth. According to Brown and Anthony (1998), the microscopic or a wear consists of abraded step fractures and center-origin spalls. Abraded step fractures occur on the anterior edge of the paraconid cusp of p2s. The bit causes step like fractures that follow the linear arrangement of enamel rods. These are then worn by the bit and through mastication, creating the abraded step fractures. The center-origin spalls are linear trenches in the occlusal ridges of enamel. A wear is diagnostic of a bit when this type of wear occurs on the paraconid cusp, but is absent from the rest of the tooth. 22

29 23 Bits also create macroscopic wear in the form of a bevel on the anterior edge of the lower p2s. The authors measured the distance between a plane projected from the second and third cusps on the lingual side of the tooth and the point where the occlusal surface meets the anterior edge. The amount of beveling in domestic horses (3.11 mm) was significantly larger than in unbitted horses (0.78 mm). Brown and Anthony (1998, 2000) noted that either a wear or beveling is sufficient evidence of the horse being bitted. They also noted that bit wear does not occur equally on both sides. Some horses will show wear only on one side, and most show preference for the left or the right side. It is important to note that the absence of bit wear does not mean that a horse was unbitted: some of the domestic horses showed no wear. The threshold beyond which such wear becomes patent has not been sufficiently well determined. In their study, the authors found that none of the unbitted horses showed any bit wear. Measurements were taken from domestic horses, as well as modern feral horses from Assateague Island and the Nevada Plains. This Brown and Anthony s study has been criticized by Levine (1999). The criticism was directed toward the size of the feral horse sample, and not the methods. This paper should serve to answer some of this criticism. This study follows these methods with a sample of wild horses completely outside the possibility of human domestication or interaction. Materials and Methods Sample of Equus for this study Two species of Equus from Leisey Shell Pit 1A were described by Hulbert (1995) and provided the sample for this analysis. Although these two species are distinct from modern caballine horses, there are enough similarities in diet and behavior of all Equus to

30 24 allow this comparison to be made (Azzaroli, 1990). The teeth are strongly hypsodont and should not differ in enamel structure or wear resistance from living species of horses. The species designations are primarily based on the metapodials and molar morphology. There should be little difficulty in comparing the p2s of these horses to those of the horses in Brown and Anthony s study. Studying these horses has several advantages that can extend the scope of study beyond what is possible with horse teeth found in archeological sites. First, this wild population of horses is 1.5 million years old. This eliminates any possible human influence. Second, rather than measuring bit wear in living animals; these horses represent a wild population that has experienced both pre and post-depositional wear. In other words, the analysis encompasses both ontogenetic wear and taphonomic wear. Bevel Measurements Following Brown and Anthony (1998) the focus on this study was on individual teeth, the lower second premolars (p2s). The main reason for this is that the major impact of grass and other food introduced into the oral cavity and manipulated by the tongue falls upon the anterior (front) edge of the second premolar. The sample size is 62 p2s in mandibles and 44 isolated lower premolars. Brown and Anthony (1998) have defined two types of wear caused by bits. Even in well-bitted horses, the horse will chew the bit unobtrusively. This causes distinctive patterns of wear on the second premolar. The first type of wear is microscopic. This is generally confined to the front or anterior end of the p2. They refer to the microscopic wear was a type wear and is defined by abraded step fractures and center-origin spalls in the enamel. These breaks are dues to high pressures being loaded to a small area. The crystal rods of enamel will splinter and break. The key to a wear is its location and

31 25 intensity. It must occur on 50% of the occlusal surface, and be either sporadic or nonexistent on the rest of the tooth. Their study used photomicrographs at 10-15x magnifications on an electron microscope. Using a light microscope at similar magnification no a type wear was visible. The second type of wear is macroscopic. In bitted horses, the bit will wear a bevel on the anterior edge of the tooth from the bit sliding back and forth (Figure 13). In Brown and Anthony s study, they used a ruler on the occlusal surface from the second to third cusps to measure the height of the bevel. It is important to maintain a right angle with the lingual side to get an accurate measurement. Instead of a ruler, I substituted a piece of right-angled aluminum (Figure 14). This way the occlusal surface could be placed on one side of the aluminum and the lingual side would be place on the other. The bevel was then measured with calipers.

32 26 Figure 13 Beveling on a domestic horse p2 Figure 14 Bevel measurements

33 27 Bevel Measurements Bevel measurements were taken on isolated p2s and p2s in mandibles. This data can be found in appendix A. Initially all premature (unworn) p2s were eliminated from the sample measured for beveling because they would not have recorded any history of utilization, regardless of whether it was with a bit or by natural mastication. Very damaged teeth were also eliminated. According to Brown and Anthony (1998), teeth with crown heights greater than 50 mm were eliminated (Figure 15). A horse less than 3 years old would have just recently lost its deciduous teeth, and malocclusions could lead to a bevel. They suggested that any tooth less than 50 mm with a length to width ratio less than 2.1 would be older than three years. They suggested that the length-width ratio be used in conjunction with crown height to eliminate deciduous teeth. It is also easy to distinguish deciduous teeth from mature by their morphology, so all teeth greater than 50mm were eliminated from the sample (Figure 17). Not all crown heights could be measured because of breakage. In these cases, the immature, unworn teeth were eliminated (Figure 18). I was able to take bevel measurements on 27 isolated teeth.

34 28 Figure 15 Separating teeth by age (crown height)

35 29 Crown Height vs Length/Width length/width crown height (mm) Figure 16 Crown height vs length/width Figure 17 Deciduous tooth

36 30 Figure 18 Immature (unworn) tooth Since crown heights could not be measured on mandibles, only those that were obviously immature or damaged were eliminated. This left a sample of 47 p2s in mandibles (Figure 19). Figure 19 Mandible

37 31 Results Statistical Tests of Bevel Measurements Descriptive statistics were calculated for all bevel measurements. There was some concern that the data may not be parametric. A chi square test was performed to test this. Since the test statistic (X 2 ) exceeded the χ 2 greater than 99.5% confidence, the data is normally distributed (Table 8) (Burt and Barber, 1996). T-tests were performed to test the differences in means between the samples (Davis, 2002). Table 8 Chi-square Test Results χ 2 D F X 2 (.995) Leisey Feral Domestic Botai Comparison of Beveling The descriptive statistics yield some interesting results (Table 9). The median is a better descriptor of the average value for highly skewed samples, or samples with a few large outliers. This is the case here. However, these numbers cannot be compared exactly. Brown and Anthony s data is rounded to a half millimeter, and my data is accurate to a tenth of a millimeter. It is also interesting to note the similarities in the mode between my sample and the feral sample. The true test of significance between the samples is the t-test (Table 9). T-tests showed that there was no difference in the means of the isolated p2s and the p2s in mandibles. The Leisey sample was then compared to Brown and Anthony s data as a whole. The Leisey data is significantly different from each of their data sets.

38 32 Table 9 Descriptive Statistics of Bevel Measurements (values in mm) Isolated Mandibles Leisey total Feral Domestic Botai Mean Median Mode Standard Deviation Sample Variance Minimum Maximum Count Table 10 t-test of Bevel Measurements Hypothesized Mean Difference Degrees of freedom Mandible vs. Isolated Domestic vs. Feral Leisey vs. Feral Domestic vs. Leisey Botai vs. Leisey Test statistic t Critical one-tail Hooks Some teeth with hooks were found (Fig 19). Brown and Anthony hypothesized that these seemed to be found on only young horse. This would possibly be the effect of deciduous teeth. However, this does not seem to be the case, since several examples were found on mature horses. It is caused by some type of malocclusion since it is not found on most teeth. Its presence would presumably not be found in a bitted horse.

39 33 Figure 20 Hooks Discussion Beveling To show that the differences in bevel measurements between feral and domestic horses Brown and Anthony (1998) merely compared the mean to the standard deviation of each group. After performing a t-test, there is a significant difference between their data (Table 8). This then enabled me to compare my data to their data. The t-test showed that the Leisey sample was significantly different from both their domestic horse and the archeological horses from the Botai site. This corroborates their hypothesis that bit wear is unique to bitted horses. However, a t-test also showed that the Leisey sample was significantly different from their feral horses. The next section will examine if ontogenetic or taphonomic wear plays a greater role in natural beveling. Their feral horses only show ontogenetic wear,

40 34 since their measurements were taken from living horses. The Leisey data should more accurately reflect wear in an archeological context, since both have a taphonomic component. Effect of Ontogenetic and Taphonomic Wear on Beveling GIS was also used to determine whether ontogenetic or taphonomic wear was more important in causing natural beveling. As shown in Chapter 2, the right teeth show a statistical difference between the distance of ontogenetic and taphonomic wear from the mean center of wear. Taphonomic wear tends to be around the outside edge of the tooth and ontogenetic wear tends toward the middle. If the anterior half of the tooth is considered in more detail one can see a difference in the two types of wear (Figure 21). Both left and right teeth tended to have taphonomic chips on the prow of the teeth (Figure 22). Ontogenetic wear tended to be spread over a larger area, encompassing the paraconid and the protoconid. Brown and Anthony (1998) state that beveling is rapidly lost if the horse is no longer bitted. If ontogenetic wear is concentrated towards the front half of the tooth then this is to be expected. A B Figures 21 A (left) and B (right) anterior half

41 35 Figure 22 Prow damage Ontogenetic wear tended to be spread over a larger area, encompassing the paraconid and the protoconid. Brown and Anthony (1998) state that beveling is rapidly lost if the horse is no longer bitted. If ontogenetic wear is concentrated towards the front half of the tooth then this is to be expected.

42 CHAPTER 4 CONCLUSIONS The GIS techniques I developed were successful in quantifying the location of wear on the occlusal surface of the teeth. It showed that there were distinct differences between life and taphonomic wear. Taphonomic wear was found evenly distributed around the teeth. This supports my initial hypothesis. This wild population of horses has different bit wear values than any of Brown and Anthony s samples. This indicates that their hypothesis that bit wear is diagnostic still holds. However, there seems to be greater variability of beveling in wild horses than they thought. The GIS study showed that natural wear tends to be evenly distributed over the surface of the teeth. Presumably, a bitted horse would show a much higher degree of damage on the mesial side of the tooth. The GIS method that I developed should prove to have many applications. It would be possible to compare Brown and Anthony s archeological specimens to the Leisey horses to determine what differences exist between the two samples. The real importance of the GIS methodology is not for a direct application of my methods, but the idea that GIS can be used to quantify any spatial data, regardless of the scale. 36

43 APPENDIX A GENERAL TEETH MEASUREMENTS Number L/R mech apl width pl pw Bevel prema saddle check Wear Roots polish ture Stage r s r s r r l p l p s l l l l r r r s r l r l s l p s r p s l l l r r s r r r s l l l l p s l l s r s r s r s r r r r r r r r p r p s r r s r r r p

44 LIST OF REFERENCES Anthony, D. A. and D. R. Brown Eneolithic horse exploitation in the Eurasion steppes: diet ritual and riding. Antiquity. 74: Azzaroli, A The genus Equus in Europe. in European Neogene Mammal Chronology. E. H. Lidsay ed. Plenum Press, New York. Azzaroli, A A synopsis of the Quaternary species of Equus in North America. Bollettino della Società Paleontologica Italiana. 34(2): Badgley, C Taphonomy of mammalian fossil remains from Siwalik rocks of Pakistan. Paleobiology, 12(2): Brown, D. R. and D. Anthony Bit Wear, Horseback Riding and the Botai Site in Kazakstan. Journal of Archaeological Science. 25: Behrensmeyer, A. K Taphonomic and ecology information from bone weathering. Paleobiology, 4(2): Behrensmeyer, A. K and A. P. Hill Fossils in the Making. The University of Chicago Press: Chicago. Behrensmeyer, A. K and S. M. Kidwell Taphonomy s contribution to paleobiology. Paleobiology. 11(1): Burt, J. E. and G. M. Barber Elementary Statistics for Geographers. The Guilford Press: New York. Davis, J. C Statistics and Data Analysis in Geology. John Wiley and Sons: New York. Fortelius, M. and N. Solounias Functional characterization of ungulate molars using the abrasion-attrition wear gradient: a new method for reconstructing paleodiets. Novitates. 33(1): Hulbert, R. C., Jr Paleoecology and population dynamics of the early Miocene (Hemingfordian) horse Parahippus leonensis from the Thomas Farm Site, Florida. Journal of Vertebrate Paleontology. 4(4): Equus from Leisey Shell Pit 1A and other Irvingtonian localities from Florida. Bull. Florida Mus. Nat. Hist. 37 Pt. II(17):

45 39 Jones, D. S Strontium isotope stratigraphy and age estimates for the Leisey Shell Pit faunas, Hillsborough County, Florida. Bull. Florida Mus. Nat. Hist. 37 Pt. I (2): Levine, M. A Botai and the origins of horse domestication. Journal of Anthropological Archaeology. 18: Lyman, R. L Vertebrate Taphonomy. Cambridge University Press: Cambridge, UK. MacFadden, B. J Magnetic polarity stratigraphy and correlation of the Leisey Shell Pits, Hillsborough County, Florida. Bull. Florida Mus. Nat. Hist. 37 Pt. I(3): Morgan, G. S. and R. C. Hulbert Jr Overview of the geology and vertebrate biochronology of the Leisey Shell Pit Local Fauna, Hillsborough County, Florida. Bull. Florida Mus. Nat. Hist. 37 Pt. I(1):1-92. Pratt, A. E. and R. C. Hulbert, Jr Taphonomy of the Terrestrial Mammals of Leisey Shell Pit 1A, Hillsborough County, Florida. Bull. Florida Mus. Nat. Hist. 37 Pt. I(7): Voorhies, M. R Taphonomy and population dynamics of an early Pliocene vertebrate fauna, Knox County, Nebraska. Univ. Wyoming Contrib. Geol., Spec. Pap. 1:1-69.

46 BIOGRAPHICAL SKETCH Christian George was born and raised in Stroudsburg, Pennsylvania. He attended Franklin and Marshall College, Lancaster, Pennsylvania, and majored in geosciences, with a minor in anthropology. His senior thesis was entitled, Taphonomic Analysis of the Fauna from Timpanogos Cave, Utah. After taking a year off from school, he enrolled in the master s program in the Department of Geological Sciences at the University of Florida. 40