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Home , Acratocnus, Ground sloth, Hapalops, Megalonychidae, Megalonyx, Mylodon

RECONSTRUCTING THE PALEODIET OF GROUND USING MICROWEAR ANALYSIS

A thesis submitted to the Kent State University Honors College in partial fulfillment of the requirements for General Honors

by

Nicholas Arthur Resar

May, 2012

Thesis written by

Nicholas Arthur Resar

Approved by

______, Advisor

______, Chair, Department of Geology

Accepted by

______, Dean, Honors College

ii TABLE OF CONTENTS

LIST OF FIGURES...... iv

LIST OF TABLES...... v

ACKNOWLEDGMENTS...... vi

CHAPTER

I. INTRODUCTION...... 1

II. MATERIALS AND METHODS...... 8

III. RESULTS...... 13

IV. DISCUSSION...... 15

V. CONCLUSSION...... 18

LITERATURE CITED...... 19

FIGURES AND TABLES...... 24

APPENDIX A. RAW MICROWEAR DATA...... 29

iii LIST OF FIGURES

Figure 1. Mean Microwear Values for Examined Taxa...... 24

Figure 2. Example image of dental microwear...... 26

iv LIST OF TABLES

Table 1. Summary statistics of genera...... 27

Table 2. ANOVA test...... 28

Table 3. Test of Homogeneity of Variance...... 28

Table 4. LSD post hoc tests for significance...... 28

v ACKNOWLEDGMENTS

I would like to thank my parents, Dale and Donna Resar, for helping me get here, and my advisor Jeremy Green for taking me under his wing. I also thank the curators at the American Museum of Natural History, New York, and the Field Museum of Natural

History, Chicago, for permitting access to tooth specimens for sampling. Finally, I would like to Dr. Carrie Schweitzer, Dr. Robert Hamilton, and Dr. Brett Ellman for serving on my defense committee. Partial funding for this project was provided by a grant from the

Kent State University Undergraduate Research Scholars Program.

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CHAPTER I

INTRODUCTION

Xenarthrans are a group of placental that include extant , tree sloths, and , as well as the extinct ground sloths and (McKenna and

Bell 1997). Among other specialized traits, such as xenarthrous articulations of the spinal column and unique articulations of the ischium (Vizcaíno and Loughry 2008), xenarthrans are differentiated from other mammals by a lack of enamel on their adult teeth (Hillson 2005). Although several clades of placental mammals have evolved partial or complete enamel loss on their teeth (Hillson 2005; Green 2009c; Ungar 2010), xenarthrans are unique in the almost universal enamel loss within the clade (Vizcaíno and

Loughry 2008). The orthodentine that composes the surface of xenarthran dentition is a softer tissue than enamel (Hillson 2005), so their teeth wear much faster compared to the enamel-covered teeth of most mammals. Because dentition is mainly used for processing food, the unique, soft, simple-shaped nature of xenarthran teeth begs the question as to what extinct members of this group were feeding upon. Although numerous in the fossil record (McDonald and De Iuliis 2008), understanding the paleoecology of extinct xenarthrans, such as ground sloths, is complicated because they lack modern ecological analogues.

Ground sloths inhabited a wide range of environments, from (McDonald

1995; Hoganson and McDonald 2007) to , including the Caribbean islands

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(White 1993) and even Antarctica (Vizcaíno and Scillato-Yane 1995). Feeding habits ranged from (Webb 1989, Shockey and Anaya 2011) and forest

(McDonald 1995; Hoganson and McDonald 2007) to aquatic feeding (de Muizon et al.

2004), and they could reach large sizes (~1000–6000 kg in some taxa; Fariña et al.

1998). Modern tree sloths, however, are limited to arboreal habitats in tropical climates

(Vizcaíno et al. 2008) and are relatively small compared to ground sloths (Gaudin and

McDonald 2008). Previous studies have applied functional morphology and biomechanical analyses to reconstruct the diet and lifestyle of ground sloths (Vizcaíno et al. 2006; Bargo et al. 2009; Shockey and Anaya 2011). As noted by Smith and Redford

(1990), anatomy is not always an accurate predictor of diet in extant xenarthrans.

Therefore, it is important to pursue as many independent lines of evidence as possible when examining diet in extinct xenarthrans.

A line of evidence just recently being explored more fully for xenarthran diet is dental microwear. Dental microwear is the microscopic scarring of the occlusal surface of teeth due to tooth-on-food or tooth-on-tooth interactions during food processing (Teaford

1991) and can take the form of scratches and pits of various widths and lengths. The type and number of microwear features depends on several factors. The more an chews its food (i.e. oral processing), the more microwear features should be deposited on the chewing (occlusal) surface of the tooth (Teaford 1991). The toughness of food particles also directly affects microwear, as tougher, more abrasive foods (e.g. grasses) are correlated with more tooth scarring (Ungar 2010). For this reason, a browser (herbivore that consumes tender leaves, fruits, etc.) should exhibit a lower density of microwear

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features than a grazer (a herbivore that primarily eats tough, abrasive grasses), as the grazer will use more oral processing to break down tougher foods (Solounias et al. 1988;

Teaford 1991; Ungar 2010). Ingested grit from either digging for food (such as roots or insects) or dust on leaves is also a major contributor to microwear formation (Williams and Kay 2001). It is also possible that the acidity of fruits in an animal’s diet will partially erase microwear (i.e. acid etching; Teaford 1988).

Analysis of microwear patterns can be conducted either qualitatively (describing overall texture or complexity), or quantitatively by measuring the size and density of features (Teaford 1991). When applied to living organisms, it is possible to correlate specific diets with specific microwear patterns; these data can be used as a foundation to reconstruct paleodiet in extinct taxa. For example, Solounias et al. (1988) compared dental morphology and dental microwear in a modern (Giraffa camelopardalis, a browser) to Grant's gazelle (Gazella granti, an intermediate feeder [an herbivore that falls between browsers and grazers]) and the wildebeest (Connochaetes taurinus, a strict grazer). They found a clear relationship between the three groups, with the giraffe having the least amount of microwear, the wildebeest having the most microwear features, and the gazelle displaying an intermediate amount (Solounias et al. 1988). The authors then looked at the extinct giraffid Samotherium boissie using both the morphological evidence and microwear analysis and found that both lines of evidence pointed towards S. boissie being a grazer (i.e. S. boissie was most similar to the wildebeest in tooth morphology and number of microwear features; Solounias et al. 1988).

While dental microwear is a well-established proxy for feeding patterns in

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mammals with enamel-covered teeth, the significance of microwear on orthodentine has received comparably less attention (Oliveira 2001; Green 2009a, 2009b). However, previous studies (Oliveira 2001; Green 2009a) have shown that xenarthrans do have microwear features on their teeth that are similar to those in other mammals, which supports the application of this technique to studying xenarthran paleoecology.

Previously, Green and Resar (2012; unpublished data) examined the microwear patterns of five extant Xenarthrans (Euphractus sexcinctus [Six-Banded ], Bradypus variegatus [Brown-Throated Three-Toed ], Choloepus didactylus [Linnaeus’ Two-

Toed Sloth], C. hoffmanni [Hoffmann’s Two-Toed Sloth], and Dasypus novemcinctus

[Nine-Banded Armadillo]), which were then grouped into one of four dietary categories.

Folivores consisted of B. variegatus, which consumes leaves from a narrow range of plant (Chiarello 2008). Frugivore-folivores consisted of C. didactylus and C. hoffmanni, which eat a more varied mixture of fruits, leaves, and flowers (Chiarello

2008). Among armadillos, insectivores consisted of D. novemcinctus, and although it primarily consumes insects, some opportunistic omnivory does occur is this group

(McDonough and Loughry 2008). Carnivore-omnivores consisted of E. sexcinctus due to its more varied diet (McDonough and Loughry 2008). The authors concluded that insectivores and folivores form a unique group that is significantly different from a separate group containing frugivore-folivores and carnivore-omnivores (Green and Resar

2012; unpublished data). In the study, insectivores and folivores consistently had a lower scratch count and higher feature width than frugivore-folivores and carnivore-omnivores

(Green and Resar 2012; unpublished data).

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Using data from this previous study on extant sloths and armadillos (Green and

Resar 2011; unpublished data), I hypothesize that dental microwear patterns can be used to reconstruct dietary niche partitioning (i.e. differences in specific diet and environment) among extinct ground sloths, thereby providing new evidence of feeding ecology in this group. I test this hypothesis by quantifying and statistically comparing microwear patterns among five taxa (, , , Thinobadistes,

Octodontotherium). Microwear in these will also be directly compared with data from extant xenarthrans, providing a basis for reconstructing feeding ecology. The five study taxa are introduced and their hypothesized paleoecology is summarized below.

Megalonyx is a North American member of the , and includes several species with a wide geographic distribution from Mexico to the Yukon, including both east and west coasts (McDonald 1995; Hoganson and McDonald 2007). Across its geographic distribution, Megalonyx is thought to be a browser living in forested areas

(McDonald 1995; Hoganson and McDonald 2007). Megalonyx specimens for this study come from the Smith pit of Levy County, , which is in age (Hulbert

2001).

Acratocnus is also a member of Megalonychidae and is closely related to extant

Choloepus (two-toed sloths; Gaudin 2004). First described by Anthony (1916), it is morphologically similar to the smaller Choloepus and has been found on several islands in the Greater Antilles (MacPhee et al. 2000). Acratocnus has been predicted to be at least partially arboreal (White 1993), but at this time, no reconstruction of diet in

Acratocnus exists. The Acratocnus specimens for this study came from the Pleistocene of

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Puerto Rico. at the time would have been an arid environment, characterized by savanna grasslands and dry scrub forests (Pregill and Olson 1981).

Hapalops is a well-documented member of the from the Santa

Cruz Formation () of Argentina. All specimens studied here came from the early

Miocene, when the Santa Cruz deposits were transitioning from a forest to a drier, more shrubby and herbaceous environment (Vizcaíno et al. 2010). It has been hypothesized that early Miocene megatheroid sloths, such as Hapalops, were leaf eaters based on morphofunctional analysis (Bargo et al. 2009). There is some debate as to whether

Hapalops was arboreal (White 1993) or better suited for digging rather than climbing

(Toledo et al. 2012).

Thinobadistes is a mylodontid sloth from the Miocene of the Gulf Coastal Plain and southern (Webb 1989). During the Miocene, Thinobadistes occupied a complex mixed environment including forest, river, and open country (Webb et al. 1981).

Very little has been published on Thinobadistes, but it has been hypothesized that mylodontids were grazers or bulk feeders in open habitats (McDonald and De Iuliis 2008;

Shockey and Anaya 2011).

Octodontotherium is another mylodontid sloth, but is known from the of the Santa Cruz Formation. Octodontotherium is one of the oldest known sloths

(Vizcaíno 2009). Like Thinobadistes, Octodontotherium is hypothesized to be a grazer

(Shockey and Anaya 2011). The Santa Cruz of the Oligocene would have been characterized by drying and cooling condition, as well as the development of open habitats that reached fulfillment in the Miocene (Shockey and Anaya 2011).

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I hypothesize that within these five taxa there will be evidence of significantly different microwear patterns between groups that will serve to distinguish between different levels of feeding ecology. This is the first study to use scanning electron microscopy in the analysis of dental microwear in extinct xenarthrans, and the only the second to use dental microwear in the study of extinct ground sloths.

CHAPTER II

MATERIALS AND METHODS

Specimen Selection.—Twenty-three specimens from six ground sloth taxa

(Megalonyx [n=6] Acratocnus [n=4]; Thinobadistes [n=6]; Octodontotherium [n=3];

Hapalops [n=3]; [n=1]) were analyzed. Specimens came from the collections at the Field Museum of Natural History, Chicago, IL

(FMNH), and the American Museum of Natural History (AMNH), New York, NY.

Standardized sampling loci should be used in xenarthran microwear analyses

(Green 2009b); here, I follow the standardized sampling protocol of Green (2009a), where the upper 2nd molariform (M2; sensu Naples 1982) was chosen for analysis for members of Tardigrada (sloths, extant and extinct (Vizcaíno and Loughry 2008b)). These specific teeth have large occlusal surfaces (relative to other molariforms in the maxilla) and also develop well-defined wear facets (Naples 1982; Smith and Redford 1990;

Vizcaíno et al. 1998); thus they are ideal targets for microwear analysis.

Molding, casting, and microscopy preparation.—For molding, the occlusal surface of teeth was first cleaned with a cotton swab using 95% ethanol or water, based on the sampling institution’s preference. Two molds were made of the entire tooth row using President Plus Jet Regular Body (Coltene-Whaledent, Inc.) impression material.

The first mold was discarded as a final cleaning step while the second mold was used for casting. A thin wall of lab putty (Lab-Putty Base/Activator, Coltene-Whaledent, Inc.) was

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then placed around the mold to provide a reservoir for casting material (i.e. Epo-Kwick epoxy resin, Buehler, Inc.). Resin was mixed at a 5:1 ratio of base to hardener, and then dribbled carefully onto the edge of the mold and allowed to seep downward to reduce the number of bubbles. Casts were placed under high vacuum for one minute, a process that was repeated at least two times to further reduce air bubbles. The resin was allowed to polymerize for at least 48 hours prior to SEM preparation.

Next, casts were mounted on either 25.4 mm or 12.7 mm aluminum (as warranted by specimen size) stubs using standard carbon adhesive tabs (Electron Microscopy

Sciences, Inc.). A belt of colloidal silver liquid (Electron Microscopy Sciences, Inc.) was then applied around the base of the specimen and the top of the aluminum stub to allow for proper electron dispersal and to improve adhesion between the stub and the specimen.

The final preparation step, accomplished just before imaging, was to coat the specimen with a thin layer of gold using a SEM Coating System (Bio-Rad Laboratories, Inc.,

Microscience Division).

Scanning Electron Microscopy.—Specimens were imaged in an Amray Model

1600 Turbo scanning electron microscope located in the Department of Geology

(McGilvery Hall) at Kent State University. Specimens were imaged at 500× with an operating voltage of 20 kV using back-scattered electrons. To help standardize the orientation of casts to the electron detector, as per the recommendation of Galbany et al.

(2004), tilt was set at 30 degrees for all specimens. Working distance ranged between 13-

25 mm, depending on the size of the tooth. Two non-overlapping images of microwear features were taken along the orthodentine band on the mesial wear facet of each tooth.

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Images from the SEM were adjusted for brightness and contrast to allow optimum viewing of microwear features. The small size of xenarthran teeth coupled with the narrow band of orthodentine made it difficult to capture photos where microwear features were consistently visible across the entire image, even at 500× magnification. To standardize the counting area, a 100 µm x 100 µm square was digitally constructed and centered over the area of highest density of visible microwear features in each image.

Brightness and contrast adjustments, as well as construction and placement of the counting square, were all accomplished using Adobe Photoshop CS4 (Adobe Systems,

Inc.).

Microwear analysis.—Scar features on 37 total images (2 images per specimen with one exception; AMNH 140855 C had only one spot of observable microwear) were analyzed using the semi-automated custom software package Microware 4.02 (Ungar,

2002). This program was originally designed for quantifying scratches and pits on enamel surfaces in mammals; however, the overall morphological similarity of orthodentine microwear features to those in enamel (i.e., Oliveira 2001; Green 2009a, 2009b; Green and Resar 2012, unpublished data) supports the use of this program for this study.

Quantification of microwear.—Microwear features were analyzed using the semi- automated custom software package Microware 4.02 (Ungar 2002). Feature counts were conducted on a Dell Dimension 4500 PC running Microsoft Windows XP Professional, with a 16 inch Dell AS500 LCD monitor. Screen resolution was maintained at 1280 x

1024 pixels. Although Microware was originally designed for quantifying scratches and pits on enamel surfaces in mammals (Ungar 1995), morphological similarity of

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orthodentine microwear features to those in enamel (Oliveira 2001; Green 2009a, 2009b;

Green and Resar 2012, unpublished data) supports the application of this program for this study.

The Microware program involves a cursor-based user interface, where the researcher identifies endpoints of scratches and pits on the image. Prior to the analysis,

Microware was calibrated with the SEM image scale bar to ensure accuracy of digital measurements. We focused on 4 variables recorded by the program: 1) number of scratches, 2) number of pits, 3) feature minor axis length (i.e., scar width), and 4) feature vector length (i.e., value R; degree of parallelism in the orientation of all features on a scale from 0 to 1). Feature major axis length is automatically recorded by the program, but I did not statistically analyze this variable because the endpoints of larger scars sometimes extended beyond the 100 µm2 counting area. The program automatically discriminates scratches from pits using a defined length/width ratio; we maintained a length/width ratio of 4:1 for our analysis. Curved features were not counted based on the limitations of the program.

Controlling for taphonomic alteration.—Since post-mortem exposure to abrasives can alter microwear patterns (Teaford 1988), specimens were checked for possible false microwear by looking at non-occlusal surfaces of the tooth. Post-mortem abrasion is unlikely to affect only the chewing surface, so a tooth showing similar microwear patterns on both the chewing and non-chewing surfaces would have to be rejected due to the likelihood of alteration to the dental microwear signature.

Statistical analysis.—All statistical tests were conducted in a PC environment

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using SPSS (Statistical Package for Social Sciences, Inc.) version 19.0. A one-way

Analysis of Variance test (ANOVA) was performed to test for the significant differences between taxa for each of the four variables. The one way ANOVA uses the F distribution to test whether significant differences between means exist (i.e. variation between groups outweighs variation within groups) at a predetermined level (α=0.05 for this study). At the same time of the ANOVA test, a test of homogeneity of variances was run on all four variables (also at significance α=0.05). Variables with equal variances (α>0.05) were further tested using Fisher’s Least Significant Difference (LSD) test, while those with unequal variances (α<0.05) were tested using the Games-Howell test. The LSD and

Games-Howell tests both examine the significance of differences between individual classes, however, the LSD test is a stronger test but it assumes equal variances.

CHAPTER III

RESULTS

Of the 23 specimens analyzed, 17 had observable microwear (see appendix A) while six specimens did not (Scelidotherium [FMNH P14450], Acratocnus [AMNH

94714], Hapalops [FMNH P13133, FMNH P13145], Octodontotherium [FMNH P13507,

FMNH P13583]). No specimens showed signs of taphonomic alteration (i.e. microwear features were confined to the chewing surface of each tooth). The results of the data are summarized in Table 1 and Figures 1a-c. Megalonyx (Figure 2a) had the widest features, the fewest scratches, and the highest degree of parallelism (R) in features (Table 1).

Acratocnus (Figure 2b) had the second widest features but the lowest R value (Table 1).

Hapalops (Figure 2c) had the narrowest features and the highest number of scratches, as well as the second highest R value (Table 1). Thinobadistes (Figure 2d) had the second narrowest feature width and the second highest number of scratches (Table 1).

Octodontotherium (Figure 2e) had the second lowest R value and the second lowest number of scratches. Typically, taxa with a lower feature width had a higher scratch number, while the number of pits and relative directionality of features was more varied

(Table 1).

The ANOVA tests revealed that only mean number of scratches varied significantly between species, although feature width was approaching significance

(P=0.053; Table 2). Both Octodontotherium and Hapalops were only represented by one

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specimen, so they were excluded from the subsequent post hoc tests. All variables were found to have equal variances (Table 3), therefore only the LSD post hoc test was used.

Thinobadistes had significantly higher scratch counts than Megalonyx, while Megalonyx had significantly wider features than Thinobadistes (Table 4). Acratocnus was not significantly different that either Megalonyx or Thinobadistes in any variable (Table 4).

CHAPTER IV

DISCUSSION

The following conclusions are based heavily on Figure 1, especially Figure 1b, comparing mean number of scratches to mean feature width. Of the examined taxa,

Megalonyx was most similar to folivores (Bradypus), which is consistent with the hypothesis that Megalonyx is a forest browser (Hoganson and McDonald, 2007). As a browser, Megalonyx would have less oral processing and hence a lower density of microwear features (Ungar et al. 2008). In this case, lower feature density was influenced by a lower number of scratches, as pits were not diagnostic (Table 1). In regards to feature width, if Megalonyx was a forest dweller, it would follow that a larger quantity of tough branches or twigs being consumed by Megalonyx could cause larger microwear features as opposed to consuming leaves.

Acratocnus most closely resembled extant frugivore-folivores (Choloepus; Table

1; Fig. 1). This is a feasible outcome, given that Acratocnus is closely related to

Choloepus (Gaudin 2004) and the predicted lifestyle of Acratocnus is arboreal (White

1993). However, some caution must be exercised before assuming that Choloepus and

Acratocnus had similar diets, since the West Indies at the time were much drier than the tropics where Choloepus lives (Pregill and Olson 1981). Therefore, it is possible that

Acratocnus consumed less fruit compared to Choloepus, and was thus filling a more intermediate browser-grazer niche.

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Octodontotherium also has similar microwear features to Choloepus, which is perhaps surprising given that Octodontotherium is predicted to be a grazer (Shockey and

Anaya 2011). Octodontotherium microwear patterns may be reflecting more an intermediate (mixed) feeding pattern, although this is difficult to test as no xenarthran mixed feeders exist today.

Hapalops and Thinobadistes both were outliers in that they had thinner features and more scratches than any other sampled xenarthran, both extinct and extant (Green and Resar 2012, unpublished data). In Thinobadistes, which is a hypothesized grazer

(McDonald and De Iuliis 2008; Shockey and Anaya 2011), microwear patterns suggest a grazing lifestyle. A high amount of oral processing is supported by the high number of scratches (Ungar et al. 2008), which in turn suggests grazing (Solounias et al. 1988).

However, this has only been shown in enamel-based studies, since there are no extant grazers that have teeth composed solely of dentine, so it is difficult to fully test this hypothesis. The low feature width, on the other hand argues for Thinobadistes ingesting either little, or fine scale, grit. Williams and Kay (2011) hypothesize that most abrasive wear on the teeth of ungulates comes from feeding near ground level. If the same held true for Thinobadistes, then it seems likely that Thinobadistes was living in grasslands and possibly grazing at a higher level.

The most interesting facet of the results from Hapalops is the low feature width relative to other taxa (Table 1). The extremely high number of scratches seen in

Hapalops illustrates that whatever it was eating, it did a lot of chewing. The low feature width suggests that it did that chewing while ingesting low levels of grit, or at least very

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little coarse grit. This is in stark contrast to what is seen in extant Dasypus and Bradypus

(Green and Resar 2011; unpublished data). Therefore, it seems unlikely that Hapalops dug up its food since that would lead to an increase in the grit in its diet and thus much coarser microwear features.

Although the results for this preliminary investigation look promising, there are several issues that need to be addressed that could limit the interpretations reached here.

The largest drawback of this study is the low number of specimens per taxon, which can lead to large standard deviations. Because the ANOVA test relies on testing the variation within a group, this can result in falsely accepting the null hypothesis that variable means of different taxa are equal. A second consequence of the low number of samples per taxon is that the sample mean may not accurately reflect the true population mean. The extreme cases of this in this study are found in Hapalops and Octodontotherium, which are both represented by only one tooth each. As such, the results of these two taxa should be viewed with additional scrutiny due to the probability that the one tooth examined could be abnormal. The second major drawback is that diet is not the only factor influencing microwear formation, but chewing mechanics and environment also influence microwear in addition to others. As such, dental microwear should not be the only factor considered when reconstructing diet but as part of a larger body of evidence.

CHAPTER V

CONCLUSION

This is the first time that the microwear patterns of several ground sloths have been analyzed and directly compared with one another. The results here support dental microwear as a valid method of examining diet in xenarthrans, given a large enough sample size. The previously hypothesized habits of Megalonyx and Thinobadistes as browsers and grazers, respectively, are supported by the data in this study. Additionally, further light was shed on Acratocnus and Octodontotherium, as both seem to have occupied a more intermediate browser-grazer role. However, this study focused on a limited number of available specimens from a narrow selection of taxa, and future studies should look at a wider range of taxa that have more specimens available. For continuing studies, further investigation should be made into taxa that have been investigated with morphological methods, particularly the South American sloths (e.g. ,

Glossotherium, , Hapalops), for which there is a large body of work. This would allow microwear analysis to be correlated against these already established methods, which would further our understanding of the usefulness of dental microwear as a tool for reconstructing paleoecology in extinct xenarthrans.

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FIGURES AND TABLES

Figure 1 – Mean values for examined taxa; a) R vs. Width; b) Number of Scratches vs.

Width; c) R vs. Number of Scratches; * denotes extant taxa

1.00 Acratocnus 0.95 Bradypus* 0.90 Choloepus* 0.85 Dasypus* 0.80 Euphractus*

0.75

R Hapalops 0.70 Megalonyx 0.65 Octodontotherium 0.60 Thinobadistes 0.55 0.50 0.45 1.0 2.0 3.0 4.0 5.0 Feature Width (µm)

24 25

50 Acratocnus Bradypus* 45 Choloepus* 40 Dasypus* Euphractus*

35 Hapalops

Megalonyx 30 Octodontotherium 25 Thinobadistes

20 Scratch Number Scratch 15

10

5

0 1.0 2.0 3.0 4.0 5.0 Feature Width (µm) 50 Acratocnus 45 Bradypus*

40 Choloepus*

35 Dasypus*

Euphractus* 30 Hapalops 25 Megalonyx 20

Scratch Number Scratch Octodontotherium 15 Thinobadistes 10

5

0 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 R

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Figure 2 – Example image of dental microwear on M2 taken at 500×, black square represents the 100µm×100µm counting square; A) Megalonyx (AMNH 140855A); B) Acratocnus (AMNH 94713); C) Hapalops (FMNH P13122); D) Thinobadistes (AMNH FAM 102672); E) Octodontotherium (FMNH P13583)

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Table 1 – Summary statistics of genera, * denotes extant taxa

Number of Number of Genus Feature Width R Pits Scratches Dasypus* average 3.98 0.76 7.40 10.00 std dev 2.25 0.13 4.86 4.69 Euphractus* average 2.18 0.64 3.71 16.36 std dev 0.73 0.17 3.36 8.95 Bradypus* average 3.71 0.66 5.60 10.75 std dev 2.43 0.19 4.81 6.92 Choloepus* average 2.46 0.72 4.50 15.17 std dev 0.88 0.22 5.49 8.57 Megalonyx mean 3.33 0.85 2.82 10.73 std dev 1.26 0.15 2.93 4.47 Hapalops mean 1.56 0.84 2.00 46.00 std dev 0.01 0.06 0.00 8.49 Acratocnus mean 2.46 0.61 3.17 18.83 std dev 1.35 0.25 2.14 10.26 Thinobadistes mean 1.67 0.65 3.08 29.58 std dev 0.39 0.27 5.18 14.46 Octodontotheriu mean 2.42 0.64 2.50 11.00 m std dev 0.17 0.04 2.12 0.00

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Table 2 – ANOVA test, significant p values are in bold

ANOVA F df P Feature Width 3.20 2,12 0.05 R 1.19 2,12 0.37 # of Pits 0.05 2,12 0.99 # of Scratches 6.15 2,12 <0.01

Table 3 – Test of Homogeneity of Variance

ANOVA F df 1 df 2 P Feature Width 2.54 2 12 0.13 R 1.98 2 12 0.18 # of Pits 1.06 2 12 0.38 # of Scratches 1.51 2 12 0.26

Table 4 – LSD post hoc tests for significance, significant p values are in bold

Megalonyx vs. Acratocnus MD SE P Feature Width 0.79 0.57 0.19 R 0.25 0.14 0.11 # of Pits -0.58 2.09 0.79 # of Scratches -7.58 5.96 0.23 Megalonyx vs. Thinobadistes Feature Width 1.59 0.46 <0.01 R 0.21 0.12 0.11 # of Pits -0.50 1.70 0.77 # of Scratches -18.33 4.87 <0.01 Thinobadistes vs. Acratocnus Feature Width -0.79 .57 0.19 R 0.04 0.14 0.78 # of Pits -0.08 2.09 0.97 # of Scratches 10.75 5.96 0.10

APENDIX A

Raw Microwear Data

Specimen Genus Width R Number of Pits Number of Scratches AMNH 140855C - 1 Megalonyx 2.41 0.971 0 17 AMNH 140855 - 2 Megalonyx 3.96 0.802 10 8 AMNH 140855 - 1 Megalonyx 2.61 0.821 2 10 AMNH 140855d -2 Megalonyx 1.79 0.965 1 15 AMNH 140855A - 2 Megalonyx 3.52 0.734 1 6 AMNH 140854 - 1 Megalonyx 4.22 0.967 3 17 AMNH 99186 - 2 Megalonyx 4.51 0.613 3 4 AMNH 99186 - 1 Megalonyx 5.96 0.577 6 6 AMNH 140855D - 1 Megalonyx 3 0.975 2 13 AMNH 140855A - 1 Megalonyx 2.83 0.952 3 11 AMNH 140854 - 2 Megalonyx 1.79 0.942 0 11 FMNH P13122 - 1 Hapalops 1.55 0.795 2 40 FMNH P13122 - 2 Hapalops 1.57 0.875 2 52 AMNH 17715 - 2 Acratocnus 4.4 0.259 6 6 AMNH 17722 - 1 Acratocnus 1.41 0.834 3 21 AMNH 17715 - 1 Acratocnus 2.31 0.601 3 18 AMNH 94713 - 1 Acratocnus 1.6 0.804 5 37 AMNH 17722 - 2 Acratocnus 1.2 0.809 0 17 AMNH 94713 - 2 Acratocnus 3.84 0.349 2 14 AMNH FAM 102698 - 2 Thinobadistes 1.18 0.889 2 44 AMNH FAM 102672 - 2 Thinobadistes 0.99 0.532 1 51 AMNH FAM 102679 - 2 Thinobadistes 1.68 0.906 1 18 AMNH FAM 102659 - 1 Thinobadistes 1.61 0.91 3 40 AMNH FAM 102679 - 1 Thinobadistes 1.51 0.73 1 18 AMNH FAM 102658 - 2 Thinobadistes 1.52 0.615 0 33 AMNH FAM 102698 - 1 Thinobadistes 2.15 0.801 2 16 AMNH FAM 102681 - 2 Thinobadistes 2.4 0.156 0 19 AMNH FAM 102681 - 1 Thinobadistes 1.51 0.536 0 15 AMNH FAM 102658 - 1 Thinobadistes 1.86 0.59 8 24 AMNH FAM 102672 - 1 Thinobadistes 1.91 0.204 1 22 AMNH FAM 102659 - 2 Thinobadistes 1.67 0.943 18 55 FMNH P13583 - 2 Octodontotherium 2.3 0.668 4 11 FMNH P13583 - 1 Octodontotherium 2.54 0.605 1 11

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