KIRTLANDIA The Cleveland Museum of Natural History March 2013 Number 58:61-72 RECONSTRUCTING PALEODIET IN GROUND SLOTHS (MAMMALIA, XENARTHRA) USING DENTAL MICROWEAR ANALYSIS NICHOLAS RESAR A. Department of Geology Kent State University, 221 McGilvrey Hall, Kent, Ohio 44242 JEREMY GREEN L. Kent State University at Tuscarawas, 330 University Drive NE, New Philadelphia, Ohio 44663 AND ROBERT K. McAFEE Department of Biological and Allied Health Sciences Ohio Northern University, 525 S. Main Street, Ada, Ohio 45810 ABSTRACT Understanding the paleoecology of extinct xenarthrans, such as ground sloths, is complicated because they lack living analogues. Previous studies have applied functional morphology and biomechanical analyses to reconstruct the diet and lifestyle ofground sloths, yet the application of dental microwear as a proxy for feeding ecology in extinct xenarthrans remains understudied. Here, we hypothesize that dental microwear patterns are statistically different among extinct ground sloths, thereby providing new evidence of feeding ecology in these animals. In a blind study, the dental microwear patterns in three extinct taxa representing two clades [Megalonyx wheatleyi and Acratocnus odontrigonus in Megalonychidae, Thinobadistes segnis in Mylodontidae] were quantitatively analyzed using scanning electron microscopy at 500X magnification. Two independent observers recovered similar relative trends in microwear patterns between M. wheat/eyi A. odontrigonus and T. segnis with mean number ofscratches and feature width being , , , the most informative variables among taxa. Microwear patterns in M. wheatleyi correspond most closely with living selective xenarthran herbivores (i.e., Bradvpus), with a low number ofscratches but a high feature width. T. segnis, in contrast, has an unusually high number ofscratches but low feature width, which is unlike any patterns exhibited by living xenarthrans and indicates possible grazing habits. A. odontrigonus falls between these two extremes, which we interpret as a more generalized browser, similar to Choloepus. Microwear patterns among living and extinct sloths sampled to date seem to fall along a continuum ofherbivorous feeding strategies, with grazing and selective browsing representing the two extremes. Although we only examine three taxa, our results (stemming from a blind analysis that accounts for observer error) support the feasibility of using high-magnification dental microwear to examine feeding ecology in extinct ground sloths. Introduction complete enamel loss on their teeth (Hillson, 2005; Green, 2009a; Xenarthrans form a majorclade ofplacental mammals (Delsuc Ungar, 2010), xenarthrans are unique in the almost universal et al., 2002) that include extant armadillos, tree sloths, and enamel loss within the clade (Vizcaino, 2009). The orthodentine anteaters, as well as the extinct ground sloths, pampatheres, and thatcomposesthesurfaceofxenarthran dentition isa softertissue glyptodonts (McKenna and Bell. 1997). Among other specialized than enamel (Hillson, 2005; Kalthoff, 2011), which causes their traits, such as xenarthrous articulations ofthe spinal column and teeth to wear much faster compared to the enamel-covered teeth the articulation between the transverse processes ofthe proximal ofother mammals. This wear is compensated for by the presence caudal vertebrae with the ischium (Vizcaino and Loughry, 2008), ofan open root, which allows for continuous growth ofthe tooth xenarthrans are differentiated from other mammals by the throughout the life of the animal. Because dentition functions absence ofenamel on their adult teeth (Hillson, 2005). Although mainly to process food, the unique, soft, simple-shaped morphol- several clades of placental mammals have evolved partial or ogy ofxenarthran teeth begs the question as to what food items 62 RESAR, GREEN, AND McAFEE No. 58 extinct members ofthis group consumed. Although ground sloth attention, until recently (Oliveira, 2001; Green, 2009b, 2009c; taxa are numerous in the Cenozoic fossil record in North and Green and Resar, 2012). Initial microwear studies on xenarthrans South America (McDonald and De Iuliis, 2008), understanding (Oliveira, 2001; Green, 2009b; Green and Resar, 2012) show that the paleoecology oftheseextinct mammals iscomplicatedbecause these enigmatic mammals do record scars on their teeth that are they lack exact living ecological analogues. similar in size and appearance to those observed in other Ground sloths inhabited a wide range of environments, mammals with enamel. Further, orthodentinemicrowear patterns stretching from Alaska to Argentina (McDonald and De Iuliis, in these animals can be statistically differentiated between taxa 2008), including the Caribbean islands (White, 1993) and possibly with different diets, although the resolution is not as high as that Antarctica (Vizcaino and Scillato-Yane, 1995; MacPhee and found in enamel studies that applythesamemethodology(Green, Regeuro, 2010). Hypothesized eating habits ranged from grazing 2009b; Green and Resar, 2012). These initial findings support the (Webb, 1989, Shockey and Anaya, 2011) and forest browsing use ofdental microwear as a proxy for xenarthran paleoecology. (McDonald, 1995; Hoganson and McDonald, 2007) to aquatic Most recently. Green and Resar (2012) examined microwear feeding (Muizon et ah, 2004), and ground sloths could have patterns in five extant species, each grouped into one of four reached large sizes (approximately1000-6000 kg in some taxa; dietary categories. Folivores consisted of Bradypus variegatus Farina et ah, 1998). Their closest living relatives, the extant tree (Linnaeus, 1758), which consumes leaves from a narrow range of sloths, however, are limited to arboreal habitats in tropical plant species (Chiarello, 2008). Frugivore-folivores were repre- climates (Vizcaino et ah, 2008) and are relatively small compared sented by Choloepusdidactyhis(Linnaeus, 1758) and C. hoffmanni to ground sloths (Gaudin and McDonald, 2008). Previous studies (Peters, 1858), which eat a more variable mixture offruits, leaves, have applied functional morphology and biomechanical analyses and flowers (Chiarello, 2008). Among armadillos, insectivores to reconstruct life history in ground sloths (Naples, 1989; were represented by Dasypus novemcinctus (Linnaeus, 1758), Vizcaino et ah, 2006; Bargo et ah, 2006a, b; Shockey and Anaya, which primarily consumes insects, although some opportunistic 2011). As noted by Smith and Redford (1990), anatomy may omnivory does occur is this group (McDonough and Loughry, not always be an accurate predictor offeeding ecology in extant 2008). Carnivore-omnivores were represented by the armadillo xenarthrans. Therefore, it is important to pursue as many Euphractus sexcinctus (Linnaeus, 1758), which has a more independent lines of evidence when examining diet in extinct variable omnivorous diet relative to other cingulates (McDo- xenarthrans. nough and Loughry, 2008). The authors concluded that relative One recent, new line ofanalysis that is being used to help better differences in the number ofscratches and width ofscar features understand paleodiet in xenarthrans is dental microwear. Dental was useful in statistically differentiating not only xenarthrans microwear refers to the microscopic scarring of the occlusal living in distinct habitats (i.e., semi-fossorial armadillos versus surface of teeth due to tooth-on-food or tooth-on-tooth arboreal tree sloths), but also taxa livingin the same habitat (e.g., interactions during mastication and can take the form of scars, two-toed tree sloths versus three-toed tree sloths; Green and such as scratches and pits of various widths, lengths, and Resar, 2012). On average, insectivorous armadillos had a lower orientations (Teaford, 1991). The type and density ofmicrowear scratch count and higher feature width than armadillos classified features depends on several factors, including, but certainly not as carnivore-omnivores. Likewise, folivorous three-toed sloths limited to, the amount of oral processing and the frequency of consistently hadlowerscratch densitywith a greaterfeaturewidth abrasives in the diet. The longer an animal chews its food (i.e., than frugivore-folivorous two-toed sloths (Green and Resar, oral processing), themoremicrowearfeaturesshould bedeposited 2012). on the chewing surface of the tooth (Teaford, 1991). The Using data from Green and Resar (2012) as a foundation, we toughness of food particles also directly affects microwear, as hypothesize that dental microwear patterns can be differentiated tougher, more abrasive foods (e.g., grasses) are correlated with among extinct ground sloths, thereby providing new evidence of higher levels of tooth scarring (Ungar et al., 2008). For this feeding ecology in this group. We test this hypothesis by reason, browsers (herbivores that consume tender leaves, fruits, quantifying and statistically comparing microwear patterns in etc.) should exhibit a lower density of microwear features than three extinct ground sloth species with microwear in living tree grazers (herbivores that primarily eat tough, abrasive grasses), as sloths (with the latter taken from Green and Resar, 2012), using the grazer will use more oral processing to break down tougher the same methodological approach as Green and Resar (2012). foods (Solounias et ah, 1988; Teaford, 1991; Ungar, 2010). Originally, we sampled six extinct taxa for this study (see Ingested grit from other sources including digging for food (such Appendix). However, post-taphonomic screening sample sizes as roots or insects) or dust on low-level vegetation is also a major for three of the taxa (Hapalops, Octodontotherium, and Sceli- contributor to microwear formation (Williams and Kay, 2001). It dotheriwn) were insufficient to provide objective information is also possible that the acidity of fruits in an animal’s diet will about paleodiet, yet the data from these few specimens can still partially erase microwear (i.e., acid etching; Teaford, 1988). help identify methodological error in our analysis. Microwear Analysis of microwear patterns can be done either qualitatively patterns in the remaining three taxa (Acratocnus, Megalonyx, and (describing overall texture or complexity), or quantitatively by Thinobadistes) wereanalyzed indetail, andweusedata from these measuring the size and density offeatures (Teaford, 1991). When three speciesto test ourhypothesis. We directlycompared ground applied to livingorganisms, it is possible to correlate specific diets sloth microwear with data from Green and Resar (2012) for with unique microwear patterns; this data can be used as a extant xenarthrans to accomplish this goal. The hypothesized foundation for reconstructing the paleodiet ofextinct taxa (e.g., paleoecology for the three primary study taxa is summarized Solounias et ah, 1988; Solounias and Semprebon, 2002; Green below. et ah, 2005). Megalonyx wheatleyi is a North American species ofthe clade While dental microwear is a well-established proxy for feeding Megalonychidae and includes several species with a wide patterns in mammals with enamel-covered teeth, the significance geographic distribution from Mexico to the Yukon, including ofmicrowear on softerorthodentine hasreceived comparably less both east and west coasts (McDonald, 1995; Hoganson and 2013 DENTAL MICROWEAR IN GROUND SLOTHS 63 McDonald, 2007). Across its wide geographic distribution, M. wheatleyi has been reconstructed as a forest-dwelling browser (McDonald, 1995; Kohn et al, 2005; Hoganson and McDonald, 2007). M. wheatleyi specimens for this study come from the McLeod Limerock Mine in Levy County, Florida, which is middle Pleistocene (Irvingtonian) in age (Hulbert, 2001). As a hypothesized strict browser, we predict that M. wheatleyi should have a lower density ofmicrowear features on its teeth relative to otherground sloths, an observation supported bydatafromliving tree sloths (Green and Resar, 2012). Acratocnus odontrigonus is also a member of Megalonychidae, and is considered more closely related to extant Choloepus (two-toed sloths) than to M. wheatleyi (Gaudin, 2004). While Acratocnus has a distribution across a number of the Great Antillesislands, thisspeciesisknown onlyfrom theQuaternary of Puerto Rico (White and MacPhee, 2001). A. odontrigonus has been reconstructedasat least partiallyarboreal (White, 1993), but Figure 1. Representative image of upper sloth molariform athtisthisspetciiemse., nA.oohdyopnottrhiegsoensusofsppeacleiomdeinestfhoarvethibseesntupdoystcualmaetedfrfoomr (iMnetghailsosntyuxd;yUwFas223a8l0w6a)y.sLaolcoantgionthoefoSrEthModiemnatginienglaanyedranoanlytshies Cerro Hueco Cave (Quaternary) in Puerto Rico (White and mesial facet of M2, indicated by the dashed crescent. Key: C, MacPhee, 2001), which, based on the associated fauna, represents cementum; Ml, molar 1; M2, molar 2; O, orthodentine; VD, an arid environment, characterized by savanna grasslands and vasodentine. Scale bar equals 3 cm. dry scrub forests (Pregill and Olson, 1981). While the bulk of Acratocnus Finds are from cave deposits, such a locality was probably not theirtypical habitat, as some sitesimplicitly indicate a trap environment (Anthony, 1916). Given the aboveground American MuseumofNatural History(AMNH), New York, NY. environments, semi-arboreal habits of these sloths, and morpho- Following the approach standardized by Green and Resar(2012), logical similarities to the feeding apparatuses of other rnega- we sampled only the mesial wear facet on upper second lonychids of all sizes (Bargo et al. 2006a, b; McAfee, 2011), we molariforms (M2; sensu Naples, 1982) for each taxon (Figure 1). suggest Acratocnus was a folivorous browser. For isolated teeth, we used direct comparison of in situ teeth in Thinobadistessegnis is a mylodontid sloth from the Miocene of maxillae (available in the collections where sampling was the GulfCoastal Plain and southern Great Plains (Webb, 1989). conducted) to positively identify isolated M2s for our analysis, During the Miocene, T. segnis occupied a complex mixed en- along with the following references: Anthony (1926); Hoffstetter vironment including forest, river, and open country (Webb et al., (1956), McDonald (1977, 1987); Scott (1904); Webb (1989). All 1981). Very little has been published on T. segnis, but it has been sample teeth for a particular species were chosen from the same hypothesized that mylodontids were grazers or bulk feeders in locality, and while this did limit sample size, the authors felt that open habitats (Moore, 1978; McDonald and De luliis, 2008; minimizingpotential intraspecificvariation in microwear patterns Shockey and Anaya, 2011), although some species have been was necessary for this introductory study. reconstructed as intermediate mixed feeders (Naples, 1989). More specifically, the broad, flat premaxilla and the correspondingly Specimen preparation wide predental spout of the mandible that is indicative of Cleaning, molding, and casting protocols for microwear Mylodontinae sloths, such as Lestodon and Glossotherium of analysis followed Green and Resar (2012). Resulting casts were South America, suggests a bulk grazing strategy (Bargo et al., mounted on 25.4 mm or 12.7 mm aluminum stubs, according 2006b). This muzzle morphology is also present in T. segnis, a to tooth size, using standard carbon adhesive tabs (Electron speciescloselyalignedwith Lestodon(Webb, 1989; Gaudin, 2004). Microscopy Sciences, Inc). A belt of colloidal silver liquid Specimens here come from Mixson's Bone Bed in Levy County, (Electron Microscopy Sciences, Inc.) was applied to the base of Florida, which is late Miocene (Hemophilia) in age (Hulbert, the specimen and the top of the aluminum stub to improve 2001; Morgan, 2005). Brief reports of the lithology of the electron dispersal and overall adhesion between the stub and the Mixson’s site appear to reflect a woodland savanna (typical of cast. The final preparation step, accomplished just before thelate MioceneenvironmentsalongtheGulfCoast; Webb 1977), imaging, was to coat the specimen with a thin layer of gold yet detailed paleoenvironmental information about this location (105 s) using a SEM Coating System (Microscience Division, Bio- is currently lacking (Leidy and Lucas, 1896; R.C. Hulbert, Jr., Rad Laboratories, Inc.). personal communication). Scanning electron microscopy Materials and Methods Foreach tooth, twodigital imagesalong theouterorthodentine Specimen selection band (Figure 1) on the mesial wear facet on M2swerecaptured at Twenty-three specimens from six taxa (Megalonyx wheatleyi 500X (with an operating voltage of 20 kV using secondary [n=6]; Acratocnusodontrigonus[n=4]; Thinobadistessegnis[n=6]; electrons) in an Amray Model 1600 Turbo scanning electron Octodontotherium grandee [n=3]; Hapalops elongates [n=3]; microscope located in McGilvery Hall at Kent State University. Scelidotherium sp. [n=l]) were analyzed (Appendix 1). Specimens To standardize thecountingarea, a 100 pm X 100 pm square was came from the vertebrate paleontology collections at the Field digitallyconstructed and centered over the area ofhighest density Museum of Natural History, Chicago, 1L (FMNH) and the ofvisible microwear features in each image. This also allowed us 64 RESAR, GREEN, AND McAFEE No. 58 to select the most opportune location to sample ante-mortem differences between observer datasets, providing a measure of microwear and to exclude areas with obvious casting artifacts. interobserver error in absolute values ofvariables. We measured Brightness, contrast adjustments, and construction of the digital the degree ofcorrelation between observerdatasets bycalculating counting square were all accomplished using Adobe Photoshop one Pearson Correlation Coefficient (PCC) per variable; this CS4 and Adobe Illustrator CS4 (Adobe Systems, Inc.). reveals whether observers recovered the same differences between species studied, regardless of absolute values (e.g., Mihlbachler Controlling for taphonomic alteration et al., 2012; Green and Resar, 2012). Following Grine et al. Since taphonomic processes can alter microwear patterns (2002), we also calculated the Mean Absolute Percent Difference (Teaford, 1988), specimens were checked for possible false (MAPD) permicrowearvariable between observers, which allows microwear by looking at non-occlusal surfaces of the tooth. us to estimate whether some variables are more error-prone Post-mortem abrasion is unlikely to affect only the chewing relative to others. surface, so teeth that showsimilarmicrowearpatternson both the Both observers independently acquired data from the same chewing and non-chewing surfaces were rejected due to the high images using a blind experimental design, so the discovery of likelihood of original microwear alteration (Teaford, 1988). In similar microwear patterns means that the two observers addition, if microwear was absent on the chewing surface of a consistently found the same type of data. This in turn suggests tooth, the specimen was also considered altered and rejected, as that additional individuals should be able to reproduce these ante-mortem microwear was most likely obliterated by tapho- results. Therefore, we analyze both observer datasets in the same nomic processes (King et ah, 1999). statistical manner to provide the most error-free, objective conclusions possible using this analytical technique. Descriptive Microwear analysis statistics were computed for both observer datasets for each variable in each dietary group. We used non-parametric Mann- tinFeomlilcorwoiwngeatrhepamtteetrhnosdosnodfigGirtaelenimaagnedsRweesraera(n2a0l1y2z)e,dourstihnogdetnh-e Whitney Uteststodetermineifsignificant interspecificdifferences exist in each observer’s dataset. semi-automated custom software package Microware 4.02 (Un- Finally, two canonical discriminant function analyses (DFA) gar, 2002). This program was originally designed to quantify were conducted (one per observer) to determine which microwear scratches and pits on enamel surfaces in mammals; however, the variables are statistically correlated with diet among extinct overall similarity of orthodentine microwear features to those in e20n1a2m)elsu(ip.pe.o,rtOlsivtehiera,us2e001o;f Gtrhiesenp,r2o0g0r9abm, cf;orGrteheisn satnuddy.ResTahre, wgirtohuntdaxsolnothass.tAhlelgfroouurpivnagrivaabrlieasblwee.rAe iWnicllkusd’edLainmbtdheaatneasltyswiass, the metric of significance for resulting functions. All statistical Microware program involves a cursor-based user interface, where the researcher identifies endpoints of scratches and pits on the tests in this study were conducted in a PC environment using image. We focused on four variables recorded by the program: 1, SPSS (Statistical Package for Social Sciences, Inc.) version 19.0. number of scratches (S); 2, number of pits (P); 3, feature minor axis length, i.e., feature width (FW); and 4, degree ofparallelism Results in feature orientation (R). Feature major axis length is Taphonomic alteration automatically recorded by the program, but we did not analyze Of the 23 specimens examined for this study, six (FMNFI FMNH FMNH FMNH thisvariablebecausetheendpointsofsomescarsextended beyond P13133, P13145, P13507, P13593, the 100 gnr counting square. We maintained a length/width ratio FMNHP 14450 (the only specimen of Scelidotherium), and AMNH of4:1 to discriminate scratches from pits. 99186) showed post-mortem obliteration of original Becausethe Microwareprogram relieson human recognition of microwear, asdescribedby Kingetal. (1999). OnespecimenofM. features, it is critical to account for operator error (Grine et al., wheatleyi (AMNH 140855-C) had only one spot of observable 2002). Additionally, knowledge of specimen identification and microwear that was deemed genuine, so only one image was dietary category assignment during analysis may lead to captured for this specimen, as opposed to two non-overlapping subconscious bias during data collection (e.g. Mihlbachler et al., images for each of the remaining teeth. After taphonomic 2012). As in Green and Resar (2012), we controlled for observer screening, H. elongatus and (). grandae were represented by only error in the following ways: 1) observers 1 (NAR) and 2 (JLG) one specimen each in our sample. Ante-mortem microwear is independently counted microwear features on all images; 2) all visible on these two remaining specimens, so we included them images were randomly organized by an independent third-party (along with unaltered specimens from A. odontrigonus, M. (i.e., not an author) and the specimen numberand species identity wheatleyi, and T. segnis) in our analysis of intra- and interob- were removed prior to counting, thus creating a blind analysis. server error to provide the most comprehensive results. However, Ten randomly selected images were duplicated within the ran- one tooth per species does not provide enough statistically useful domized image file. These duplicates were analyzed alongwith all information to reconstruct paleodiet, as there is no measure of other images, which allowed us to measure intraobserver error in populational variation in microwear. Thus, H. elongatus and O. the consistency offeature recognition by both researchers. grandae were not included in our statistical analysis of interspe- Eight non-parametric Wilcoxon signed-rank tests [one per cific microwear patterns; only data from unaltered A. odontrigo- variable (4) per observer (2)] were applied to determine if each nus, M. wheatleyi, and 7. segnis specimens were statistically observer consistently recognized the same numbers of features analyzed for interspecific microwear differences. between iterations ofthe duplicate images. We did not re-analyze images more than once because repeated iterations can lead to Observer error observer familiarity with images, which can falsely deflate error Wilcoxon signed-rank tests for intraobserver error revealed measurements (Mihlbachler et al., 2012). Four Wilcoxon signed- very little difference amongvariables between replicate images for rank tests (one per variable) were applied to test for significant either observer; only R varied significantly for observer 2 1 1 2013 DENTAL MICROWEAR IN GROUND SLOTHS 65 Table 1. Results from Wilcoxon signed-rank tests for significant Table 3. Mean Absolute Percentage Differences (MAPD) for differences in variables both between and among independent all variables between observers. Variable abbreviations follow observers. Significant p-valuesare in bold. Variable abbreviations the text. follow the text. Key: Z, z value. Microvvear variable Observer 1 Observer2 Combined mean MAPD Observer I Observer2 S 20.76 30.35 14.78 18.76% Microvvearvariable Z p Z p P 2.85 6.97 4.91 41.96% FW 2.43 2.26 2.35 3.40% Intraobserver Differences R 0.72 0.68 0.70 2.85% FW -0.26 0.80 -0.92 0.36 R -0.46 0.65 -2.09 0.04 P -1.72 0.09 -0.56 0.57 recorded a total percent correct classification of 93.30% for all S -0.26 0.80 -1.26 0.21 specimens analyzed (Table 8). Interobserver Differences(Observer I vs. Observer2) FW -0.73 0.46 Discussion R -1.56 0.1 P -3.42 <0.01 Observer error S -3.01 <0.01 With theexception ofR forobserver2, both observerswereable toconsistently recognizeand identifythe samemicrowearvariables on replicate images (Table I). However, because R was not (Table 1). However, two out of four variables (S, P) varied unanimously significant in diagnosing interspecific microwear in significantly between observers (Table 1). PCCs for each variable ground sloths (discussed further below; Table 5), significant revealed a high degree of correlation between observer datasets observer variation in this variable does not hinder our overall bt(h4eo2lu%og;whT,tahwbeilte0.h031)t,hrlweehveielloef(mTtaehbealnevaRr2)i.ahbMaldeesatn(hSe,PlFohWwae,sdtRt()h3e%b;ehiiTgnahgebslstiegnM3i)f.AicPanDt e(anrTaralobyrlseilse.1v)e;Blsestuwwceehreeninpotrbeesrseoerbnvsteerrisvn,ertbhoeetrhprromerevaiisonunsSotaannaudlnyPcsiovsamrmoifoendm,isicgarnsoiwfsieicamarinltaliryn extant xenarthrans (Green and Resar, 2012) and have been also Microwear statistics recorded in enamel microwear studies (e.g., Grine et al., 2002; A total of 25 images from M. wheatleyi, T. segnis., and A. Purnell et al., 2006; Mihlbachleret al., 2012). While S and Pvaried odontrigonus were analyzed for interspecific differences in micro- significantly between observers, it follows reason that FW and R wear using descriptive, ANOVA/Welch and DFA statistical tests would notvaryasmuch.Theexpectedaverage ofa randomsample to address the hypothesis that there are significant differences fromapopulationshouldbeapproximatelythesameasthemeanof between taxa that can be used to differentiate feeding ecology. theentirepopulation, regardlessofsample size. Given that S and P For both observers, T. segnis had the highest scratch count and are counts, they would differ significantly based on the number of lowestfeaturewidth,whereasM. wheatleyihad thelowestnumber features identified. However, FW and R, beingaveragescalculated of scratches and greatest feature width (Table 4; Figures 2-3). from a sample offeatures identified in the image, are approximate For both of these variables, A. odontrigonus had intermediate tothetruemeanfortheentireimage,eventhoughthefeaturecounts values, relative to the other species (Table 4; Figures 2-3). maydifferbetweenobservers. FWand R should besimilarbetween Mann-Whitney U tests revealedmean S and FW as statistically both observers because they are looking at the same image. different between M. wheatleyi and T. segnis (Table 5). However, MAPD for our variables are relatively comparable with those neither mean S nor mean FW could statistically distinguish A. reported in Green and Resar (2012), with the error being highest odontrigonus from the other two analyzed taxa (Table 5). in P and S and lowest among FW and R (Table 3). However, Observer 2 found that R and P were significant in distinguishing absolutevaluesfor MAPDsin ourstudy(with theexception ofR) A. odontrigonus from M. wheatleyi, but observer I did not are higher than that of extant xenarthrans (Table 3). This corroborate this result (Table 5). increased relative error between observers may be inflated by To discriminate further between these three ground sloths, two the sheer density of microwear features in taxa such as canonical functions were formed by SPSS for each observer’s Thinohadistes (Figure 3C), where number of fine-scale scratches DFA. Function 1 explains the majority of the variance and is is high, causing some inconsistency between observers. statistically significant for both observers, whereas function 2 is However, even though interobserver variation is present, PCCs never significant (Table 6). Mean S has the highest correlation still revealed significant correlations for three variables (FW, S, with function 1 for both observers, with mean FW also correlated R; Table 2). Thus, while absolute values may differ between with function 1 only in observer 2 (Table 7). Both observers observers, independent observers consistently identified similar relative patterns under blind conditions in our analysis. This Table 2. Pearson Correlation Coefficients (PCC) for data sets finding, coupled with the presence of similar interobserver bSiegtnwiefeicnanOtbspe-rvvaelruess1araendin2,bolodr.ganViazreiadblbeyambibcrervoiwaetaironsvarfioalblloe.w csourprpeolrattsiotnhse ianppleixctaatnitonxeonfarhtihgrha-nmsagn(iGfrieceantioanndSERMesamri,cr2o0w1e2a)r, the text. analysis for reconstructing paleoecology in ground sloths. Microvvearvariable PCC Variable significance l> FW 0.76 <0.01 To avoid subjectivity in microwear studies, reproducibility in R 0.79 <0.01 observer data should be assessed before interpretation and, P 0.40 0.1 ideally, only repeated results between multiple, independent S 0.77 <0.01 observers should be accepted. Following these criteria, we can 66 RESAR, GREEN, AND McAFEE No. 58 Table 4. Mean values ofmicrowear variables recorded by two independent observers for five extant xenarthran species (grouped by dietary category, labeled in bold in the specimen column). Variable abbreviations follow the text. Key: AMNH, American Museum of Natural History; FMNH, Field Museum ofNatural History. Observer 1 Observer2 Specimen FW R P S FW R P S A. odontrigonus AMNH 17722 1.31 0.82 1.50 19.00 1.23 0.75 8.50 27.50 AMNH 94713 2.72 0.58 3.50 25.50 2.03 0.51 13.00 40.50 AMNH 17715 3.36 0.43 4.50 12.00 3.26 0.47 11.00 18.50 GroupAverage(SD) 2.46(1.05) 0.61 (0.20) 3.17(1.53) 18.83(6.75) 2.17(1.02) 0.58(0.15) 10.83(2.25) 28.83(11.06) H. elongatus FMNH P13122 1.56 0.84 2.00 46.00 2.17 0.57 4.00 30.00 M. wheatleyi AMNH 140854 3.01 0.95 1.50 14.00 2.10 0.79 5.50 23.00 AMNH 140855-A 3.18 0.84 2.00 8.50 1.92 0.72 2.00 16.00 AMNH 140855-B 3.29 0.81 6.00 9.00 3.63 0.93 7.00 10.50 AMNH AMNH 140855-C 2.97 0.85 0.50 11.50 2.13 0.76 5.00 36.00 140855-D 2.40 0.97 1.50 14.00 3.02 0.96 7.00 16.00 AMNH 99186 5.24 0.60 4.50 5.00 3.70 0.93 7.00 11.00 Group Average(SD) 3.35(0.98) 0.84(0.13) 2.67(2.11) 10.33(3.52) 2.75(0.81) 0.85(0.10) 5.58(1.96) 18.75(9.58) O.grandae FMNH P13583 2.42 0.64 2.50 11.00 2.86 0.40 7.50 15.00 T. segnis AMNH FAM 102658 1.69 0.60 4.00 28.50 1.45 0.64 10.00 57.00 AMNH FAM 102672 1.45 0.37 1.00 36.50 1.59 0.17 13.50 46.50 FMNH 28354 1.67 0.85 2.00 30.00 1.42 0.83 4.00 47.50 FMNH 34347 1.64 0.93 10.50 47.50 1.90 0.91 9.50 57.50 FMNH 34348 1.60 0.82 1.00 18.00 1.57 0.77 3.00 36.00 Group Average(SD) 1.67(0.17) 0.65(0.25) 3.08(3.88) 29.58(11.51) 1.73(0.38) 0.62(0.29) 6.83(4.87) 45.33(11.79) be reasonably certain that our interpretations of paleodiet from (Choloepus) through the presence of lower mean S and higher microwear are as unbiased as possible (e.g., Mihbachler et al., mean FW values relative to other sampled taxa (Table 5, 2012). In our study, although there is a high degree ofcorrelation Figure 2; Green and Resar, 2012). This result supports the between observer datasets, there were some mixed results from hypothesis that M. wheatleyi was a forest browser. As a statistical tests between observers. hypothesized browser, we predicted that M. wheatleyi should Both observers found that variables S and FW revealed the have less oral processing and hence a lower density ofmicrowear same significant distinction among sampled ground sloths using features (Ungar et al. 2008). Since oral processing (orchewing) is Mann-Whitney U tests (Tables 5-8). In contrast, when DFA correlated with the formation of microwear features, more results are considered, the only variable that was shared between chewing usually leads to more microwear features. Browsers, observers for function 1 (the only significant function in both herbivores that are more selective about what plants they are analyses; Table 6) was FW. Variable S, in addition to FW, was eating and typically feed on softer leaves, have less need to chew important to function 1 only for observer 2 (Table 7). and therefore are predicted tohavefewermicrowearfeatures than We conclude that both variables FW and S have the highest grazers, who feed more indiscriminately and on tougher significance in reconstructing paleoecology from microwear in vegetation (Teaford, 1991; Ungar et al., 2008). We support this extinct ground sloths. These two variables yielded significant prediction, reporting lower feature density in M. wheatleyi, results between observers, although the significance of each relative to other ground sloths (Figure 3), which results from a variable is, in some cases, dependent on the nature of the significantly lower number ofscratches (Tables 4-6). Consuming statistical test. Nevertheless, significant PCCs for S and FW a large quantity of tough branches or twigs may account for suggest that both observers recorded the same relative patterns relatively wider scars in M. wheatleyi relative to A. odontrigonus between species, which supports a genuine interspecific pattern. and T. segnis. Thesimilarity ofM. wheatleyito both extant sloths Although observer 2 found that R and Pwere significant between suggests that it may have had a more varied diet than Bradypus, A. odontrigonusand M. wheatleyi, observer 1 did not corroborate but lessvaried than that ofCholoepus. Incontrast toextant sloths, this result (Table 5); this discrepancy, coupled with the presence however, Megalonyx would have been feeding at a much lower of significant intraobserver error in R for observer 1 (Table 1) level (i.e., ground-dwelling niche; Hoganson and McDonald, calls into question the validity ofthis result. Thus, R and P likely 2007), so a larger and/or different selection of available browse have no significance in distinguishing ground sloth taxa in our may be reflected by microwear. Overall, our results support study and we do not consider these variables further in this study. previous hypotheses, drawn from independent lines of evidence (e.g., Hoganson and McDonald, 2007), that M. wheatleyi Interpretation of feeding ecology occupied a forest browsing niche during the Quaternary in Oftheexamined taxa, Megcilonyxwheatleyiwasmost similarto Florida and likely in other parts of its North American extant xenarthran folivores (Bradypus) and frugivore-folivores distribution (e.g., Kohn et al., 2005). 2013 DENTAL MICROWEAR IN GROUND SLOTHS 67 35 CsAcratocnus OBradypus* 30 ACholoepus* OMegalonyx 25 Thinobadistes 20 -C E 15 10 5 o 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 A FeatureWidth (pm) AAcratocnus 50 OBradypus* ACholoepus* OMegalonyx 40 Thinobadistes <D .D z Sui 4-* E u tA 20 10 0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 FeatureWidth (pm) Figure 2. Graph ofmean feature width (FW) vs. scratch number (S) for both observers; A, Observer 1; B, Observer 2. * denotes extant taxa (taken from Green and Resar, 2012). Microwear in Thinobadistes segnis was anomalous in that we considered general grazers (Moore, 1978; McDonald and De consistently observed thinner scratches in a much higher density luliis, 2008; Shockey and Anaya, 2011) or possibly mixed feeders on its teeth than any other sampled xenarthran to date, both (Naples, 1989), diets usually correlated with increased oral extinct and extant (Table 4; Figures 2-3). Mylodontids are processing relative to browsers (Ungar et al., 2008). A relatively 1 68 RESAR, GREEN, AND McAFEE No. 58 Table 5. Mann Whitney U tests for data from both observers. Significant p-valuesare in bold. Variable abbreviations follow the text. Key: Z, z value. Observer 1 Observer2 Z P z P Aeratocnusvs. Megalonyx s -1.82 0.07 -1.56 0.12 p -0.40 0.70 -2.36 0.02 FW -0.78 0.44 -1.03 0.30 R -1.81 0.07 -2.07 0.04 Aautocallsvs. Thinobadistes S -1.29 0.20 -1.69 0.09 P -0.78 0.44 -1.03 0.30 FW -0.78 0.44 -0.52 0.61 R -0.39 0.70 -0.52 0.61 Megalonyxvs. Thinobadistes S -2.89 <0.01 -2.65 0.01 P -0.40 0.69 -0.32 0.75 FW -2.88 <0.01 -2.40 0.02 R -1.29 0.20 -1.60 0.1 high scratch density in T. segnis supports high amounts of oral processing(Ungaret al., 2008), which in turn suggeststhepossible inclusion of tough, abrasive vegetation, such as grass, in the regular diet ofthis taxon (Solounias et al. 1988). Therefore, it is possible that T. segnis occupied a mainly grazing niche in the Miocene savannas of Florida. However, we note that the correlation between high scratch density and grazing only exists in enamel-based microwear studies (Solounias et al., 1988; Teaford, 1991; Solounias and Semprebon, 2002); there are no extant grazers thathaveteethcomposed solelyoforthodentine, so it is difficult to fully test this hypothesis. As an alternate FW hypothesis, the high scratch density and relatively low could come from the consumption of high amounts of fine-scale grit, which accumulates near ground level in open habitats (Williams and Kay, 2001). The paleoenvironment of Mixson’s bone bed is not as well understood as that of contemporary Miocene environments in Florida (e.g.. Fove Bone Bed; Hulbert, 2001), yet current evidence suggests an open, savanna-like environment (Feidy and Fucas, 1896; R.C. Hulbert, Jr., personal communica- tion). This observation, coupled with smaller body size (about 450 kg; McDonald. 2005) that suggests low-level feeding habits (e.g., Webb, 1989), supports the inclusion ofgrit during feeding, and/or possibly a diet that consisted mainly of abrasive grasses and vegetation. T. segnis may very well have been a grazer in the Miocene grasslands, but supporting empirical evidence for grazing in this taxon is currently lacking. Aeratocnus odontrigonus most closely resembled extant frugi- vore-folivores (Choloepus) in terms of S and FW (Figure 2). The predicted lifestyle ofA. odontrigonus is at least semi-arboreal, and may have been somewhat similar to the obligate arboreal role of living two-toed sloths (White, 1993). Among extant xenarthrans, microwear patterns are significantly different between ground- dwelling forms versus strictly arboreal taxa, thereby reflecting habitatoccupancyasmuchasdietarydifferences(GreenandResar, Figure 3. Examples of dental microwear on ground sloths M2s taken at 500X; black square represents the 100 pmXlOO pm B, Aeratocnus odontrigonus (AMNH 17715); C, Thinobadistes counting square; A, Megalonyx wheatleyi (AMNH 140855-A); segnis (AMNH FAM 102672). 2013 DENTAL MICROWEAR IN GROUND SLOTHS 69 Table 6. Variance and significance of generated discriminant Table 8. Probabilities from DFA classification matrix for each functions for each observer’s DFA. Significant p-values are in observer. Bold values indicate total percent correct classification bold. Key: %V, percent of total variance described by each per taxon. function; df, degrees of freedom; p. p-value; WL, Wilks’ Lambda value. Observer Taxon A. odontrigonus M. wheatleyi T. segnis 1 %Correct A. odontrigonus 100.00 0.00 0.00 Observer 1 Observer2 M. wheatleyi 0.00 100.00 0.00 Function %v WL df P %v WL df P % T. segnis 16.70 0.00 83.30 2 Correct A. odontrigonus 100.00 0.00 0.00 1 97.30 0.14 8 <0.01 80.30 0.14 8 <0.01 M. wheatleyi 0.00 83.30 16.70 2 2.70 0.88 3 0.71 19.70 0.58 3 0.12 T. segnis 0.00 0.00 100.00 2012). Ourresultssupport theviewofA. odontrigonusoccupyingat these graphs represent a browser-grazer continuum of herbivo- least a semi-arboreal habitat in the Quaternary of Puerto Rico. rous feeding strategies in xenarthrans, with selective browsers However, we exercise caution in assuming that Choloepus and A. (Bradypus) representing the lower right extreme and grazers odontrigonus had similar diets, because the West Indies during the occupyingthe upper leftextreme. In this scenario, T. segniswould Quaternary were much drier than the tropical regions where be a grazer, whereas Choloepus and Acractocnus(existing nearthe Choloepusresides today (Pregill and Olson 1981). Itis possible that middle ofthe continuum) might be interpreted as more generalist A. odontrigonus was herbivorous and engaged in a browsing browsers. Megalonyx always occupies the space between Choloe- folivorous habit akin to that of Choloepus due to their close pus and Bradypus, suggesting (under this scenario) that it was a phylogenetic affinity (White et ah, 2001; Gaudin, 2004), and the more specialized browser than Choloepus, but less so than differences perhaps reflect different amounts of grit or abrasive Bradypus. This last interpretation mirrors paleoecological recon- particleswithintheopposingplantmatterconstitutingthetwodiets. structions ofMegalonyx from independent lines ofevidence (e.g., Neocnus, another Caribbean meglonychid with close affinities to Kohn et ah, 2005; Hoganson and McDonald, 2007). It is also Acratocnus and Choloepus (White and MacPhee, 2001; Gaudin, interesting to note that Figure 2 also separates the sloths into 2004), has also been suggested as an arboreal folivore but with a phylogenetic groupings with the megalonychids (Acratocnus, feeding strategy more similar to that ofBradypus (McAfee, 201 1), Clioleopus and Megaloynx) all occupying the middle range while , further highlighting the potential differences for dietary strategies the extremes are held by a mylodontids (Thinobadistes) and a and the need for independent lines ofevidence. bradypodid (Bradypus), which could indicate that portions ofthe Ofthe three taxa statistically analyzed (M. wheatleyi, T. segnis, feeding spectrum have their roots in phylogenetic relationships. and A. odontrigonus), only M. wheatleyi and T. segnis were These hypotheses remain to be tested by futuremicrowear studies statistically differentiable (in terms of S and FW; Table 5). This and increased analysis of paleodiet in sloths by applying this leaves A. odontrigonus as indistinguishable from the other two technique to a wider variety oftaxa. taxa (Table 5). There are two probable explanations for this FW occurrence. First, A. odontrigonus has values for S and in Conclusions abnetwabeseonluTt.esedginfifseraenndceMb.etwhweeaetnleiytis (mFeiagunreva2l)ueasndanthdusthhoasseleosfsoT.f ofTomulotuirplkenowelxteidngcet, tghrisouinsdtheslfiortshtstihmaevtehatbemeincroawneaalryzpeadttearnnds segnis and M. wheatleyi. Second, A. odontrigonus was represented statistically compared to data from living xenarthrans to better by fewer specimens than either T. segnis or M. wheatleyi in our understand the paleoecology of this group. Our results support study (Table 4), whiFchWmay obscure statistical significance. high-magnification orthodentine microwear analysis as a valid in addition, S vs. plots between observers reveal a repeated method of examining diet in xenarthrans, given a large enough trend, in that microwear patterns amongxenarthrans (both living sample size. The previously hypothesized lifestyle of M. wheatleyi and extinct) appears to exist on a continuum(Figure 2). Bradypus as a forest browser (McDonald 1995; Hoganson and McDonald, represents one extreme of this spectrum, whereas T. segnis 2007) is supported by a low number ofscratches and wide scars, a represents the other extreme, with Acractocnus Choloepus and Megalonyx occupying the middle range (Figure, 2). The di,et of fpoaltitveronroutshatthreise-qtuoaendtistlaotthisv.elAyddiidteinotniaclally,towemiscugrgoewsetarthaitnalihviignhg living Bradypus and Choloepus is selectively folivorous in the numberofscratchesandlowerscarwidth in T. segnissuggestshigh former and more generalized browsing in the latter. It is possible levels ofgrit in the diet, either from dust accumulating on ground level vegetation or from abrasive grasses, or possibly a mixture of these two suggestions. Our study focused on a limited number of Table 7. Discriminant function structure matrix. Values marked available specimens from a narrow selection oftaxa, which limits with an asterisk (*) reveal thelargest absolutecorrelation between theoverallconclusionsthatwecan reasonablydrawfromourdata. that variable and the corresponding discriminant function. Whatisrelevantat thistimeisthatwemustnotethatourrespective Variable abbreviati1ons fol2low the text. 12 ground sloths represent taxa from different ages, climates, and habitats (e.g.. Pleistocene forests, tropical and temperate, versus Observer 1 Observer 2 Miocenesavannas).Therefore,thedrasticdifferencesinmicrowear Function notedbetween M. wheatleyiand T. segnismaystemfromintangible FW 0.47* -0.40 0.70* -0.32 variation in environmental conditions, rather than strictly from S -0.50 0.66* -0.38* 0.32 diet. However, because orthodentine microwear reveals distinct R 0.22 0.59* -0.14 -0.72* feeding differences in living xenarthrans that occupy different P -0.34 -0.86* -0.24 0.59* environments (e.g., semi-fossorial armadillos versus arboreal 70 RESAR, GREEN, AND McAFEE No. 58 sloths; Green and Resar, 2012), we suggest that the differences we Chiarello, A. G. 2008. Sloth ecology: an overview of field report here are reflective ofdifferences in feeding ecology. studies, p. 269-280., In S. F. Vizcaino and W. J. Loughry This initial work reveals that paleoecological signals should be (eds.), The Biology of the Xenarthra. University Press of Florida, Gainesville. recorded in fossil ground sloth teeth, provided post-mortem alteration has been taken into account. Future studies should Cope. E. D. 1871. Preliminary report on thevertebratadiscovered look at a widerrangeoftaxathat havemore specimens available, in the Port Kennedy Bone Cave. American Philosophical including fossil cingulate taxa. We also suggest that future Society, 12:73-102. microwear studies in extinct xenarthrans examine different taxa Delsuc, F., M. Scally, O. Madsen, M. J. Stanhope, W. W. de that co-occurat the same locality, such as Rancho La Brea, rather Jong, F. M. Catzeflis, M. S. Springer, and E. J. P. Douzery. than from chronologically different localities. Analysis of stable 2002. Molecular phylogeny of living xenarthrans and the impact of character and taxon sampling on the placental isotopes in xenarthran teeth may yield comparative information tree rooting. Molecular Biology and Evolution, 19:1656- regardingpaleodiet. Xenarthran orthodentinemaybelessproneto 1671. diagenetic alteration that originally assumed (MacFadden et al., 2010). However, there remain complications that need to be Farina, R. A., S. F. Vizcaino, and M. S. Bargo. 1998. Body mass estimations in Lujanian (late Pleistocene-early Holocene of resolved before the geochemical signal of orthodentine can be South America) mammal megafauna. Mastozoologia Neo- objectively interpreted (MacFadden et al., 2010). More broadly, tropical, 5:87-108. further investigation should be made into taxa that have been investigated with morphological methods, particularly the South Gaudin. T. J. 2004. Phylogenetic relationships among sloths (Mammalia,Xenarthra,Tardigrada):thecraniodentalevidence. American sloths (e.g.. Megatherium, Glossotherium, Mylodon, Zoological Journal ofthe Linnean Society, 140:255-305. Hapalops, and Scelidotherium), for which there is a large body of work(e.g., Bargoetal., 2006a,b;Vizcainoetal.,2006).Thiswould Gaudin. T. J.. and H. G. McDonald. 2008. Morphology-based investigations of the phylogenetic relationships among extant allow microwear analysis to be correlated against these already and fossil xenarthrans, p. 24—36., In S. F. Vizcaino and W. J. established methods, and would further our understanding ofthe Loughry (eds.), The Biology of the Xenarthra. University usefulness ofdental microwearas a tool forreconstructingfeeding Press of Florida, Gainesville. ecology in extinct xenarthrans. Green, J. L. 2009a. Enamel-reduction and orthodentine in Dicynodontia (Therapsida) and Xenarthra (Mammalia): an Acknowledgements evaluation ofthe potential ecological signal revealed by dental We thank the collections staff and curators at the American microwear. Ph D. dissertation. North Carolina State Univer- Museum of Natural History (Alana Gishlick, Carl Mehling. Jin sity, Raleigh. Meng, Ruth O’Leary) and the Field Museum ofNatural History Green, J. L. 2009b. Dental microwear in the orthodentine ofthe (K. Angielczyk,WilliamSimpson)forpermittingsamplingoffossil Xenarthra (Mammalia) and its use in reconstructing the teeth for our study. David Waugh and Merida Keatts provided paleodiet of extinct taxa: the case study of Nothrotheriops technical assistance; Richard Hulbert, Jr. provided background shastensis (Xenarthra, Tardigrada, Nothrotheriidae). Zoolog- ical Journal ofthe Linnean Society, 156:201-222. information on Florida fossil localities; Carrie Schweitzer and Rodney Feldman allowed access to lab facilities for casting and Green, J. L. 2009c. Intertooth variation of orthodentine micro- SEM preparation; Kathryn Green helpedcreatetheblind analysis. wear in armadillos(Cingulata)and treesloths(Pilosa). Journal We thank Gregory McDonald, Matthew Mihlbachler, and one of Mammalogy, 90:768-778. anonymousreviewerforprovidinghelpfulcommentsonthispaper. Green, J. L., and N. A. Resar. 2012. The link between dental We also thank Peter Ungar for providingaccess to the Microware microwear and feeding ecology in tree sloths and armadillos. 4.02 software. The University Research Council and the Research Biological Journal ofthe Linnean Society, 107:277-294. Scholars Undergraduate Program at Kent State University Green, J. L., G. M. Semprebon, and N. Solounias. 2005. provided partial funding for this project. Reconstructingthepalaeodiet ofFloridaMammutamericanum via low-magnification stereomicroscopy. Palaeogeography, Palaeoclimatology. Palaeoecology, 222:34-^48. References Grine, F. E., P. S. Ungar, and M. F. Teaford. 2002. Errorrates in Ameghino, F. 1894. 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