AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 84:59-73 (1991)

Deciduous Dental Microwear of Prehistoric Juveniles From the Lower Illinois River Valley JILL BULLINGTON Department of Anthropology, Northwestern University, Euanston, Illinois 60208

KEY WORDS

Weaning diet, Age-related tooth wear

ABSTRACT

Scanning electron microscopy was used to study age-related changes in the dental microwear of 36 prehistoric juveniles ranging from 6 to 27 months of age. Juveniles from horticultural (Middle Woodland) and agricultural (Mississippian) groups were studied to allow an investigation of the impact of diet on deciduous microwear. Inclusion of both molars and incisors in the sample permitted identification of age at earliest appearance of wear and comparisons between the age-related microwear characterizing different tooth types. Data on feature frequency and enamel surface characteristics were analyzed. Microwear feature frequencies generally increase with age and/or exposure to wear. Enamel surface characteristics show consistent qualitative changes associated with both age and exposure to wear. Molars and incisors differ for such surface characteristics in a way that make biomechanical sense, given the relative bite forces characterizing these teeth. Dietary reconstruction based on deciduous microwear is complex because of the effects of both age and exposure to wear on feature frequencies and enamel surface characteristics. Nonetheless, the present analyses suggest that 1) diets differed for younger and older juveniles within each cultural group and 2) the Middle Woodland juvenile diet was both harder and more varied in physical consistency than the Mississippian juvenile diet.

The majority of dental microwear research to date has sought to identify either diet or jaw movements (see, e.g., Grine, 1981,1986; Harmon and Rose, 1988; Kelley, 1986; Teaford, 1985; Teaford and Oyen, 1989; Teaford and Robinson, 1989; Teaford and Walker, 1984; Rensberger, 1978; Ryan, 1980, 1981; A. Walker, 1981; Walker et al., 1978; P. Walker, 1976).An important exception to these trends is provided by Gordon’s (1980, 1982) investigations of nondietary sources of variability in the dental microwear of adolescent and adult chimpanzees. Her suggestion that dental microwear varies with age has recently been explored in a study of age-related microwear in vervets (Teaford and Oyen, 1986, 1988, 1989). To date, however, microwear characterizing the deciduous dentition has not been investigated. The deciduous teeth of very young individuals provide a source of information on age-related microwear, including both earliest appearance and subsequent devel@ 1991 WILEY-LISS. INC.

opment. The present study focuses upon a erelated dental microwear changes in the eciduous teeth of 36 prehistoric juveniles. These juveniles, ranging in age from 6 to 27 months, represent two cultural groups with archaeologically well-documented dietary differences. This research seeks to identify the onset and earliest development of microwear in the deciduous dentition and to determine whether age at onset and subsequent age-related atterning vary between cultural groups wit differing diets. Ages at sevrage (cessation of breast feeding) and weaning (introduction of other foods) vary widely in traditional societies. Moreover, these two events rarely coincide: breastfeeding usually continues after supplemental foods are introduced into the infant diet (Jelliffe and Jelliffe, 1978). Identifying the age at onset of microwear is

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Received June 22,1989; accepted April 26,1990.

60

J. BULLINGTON

relevant to stud ing a e at weanin rather than sevrage. thoug it is proba le that many, if not all, of the individuals in this sample were still breast feeding, it is unlikely that most were exclusively breast fed. Ethnographic data show that supplemental foods are introduced during the first few months of life in most traditional societies (Hull and Simpson, 1985; Ra hael, 1979) and that the availability of so t foods is an important factor in the timing of this event (Hull and Simpson, 1985). Moreover, there appears to be a critical period of development, between approximately 4 and 9 months of age, during which infants must learn to chew food or they will develo severe feeding roblems (Schmitz and d N e i s h , 1987). dthough it is impossible to predict exact ages at weaning for the infants studied here, modern data on weanin strongly suggest that this event occurred cfuring the first year of life.

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human bone (van der Merwe and Vogel, 1978). Locally, maize consum tion ap ears to have reduced rather than e iminate consumption of other foods; archeobotanical remains sug est that the Mississippian diet included afower roportion of the nuts and hard starchy see s so abundant in the Middle Woodland diet (Johannessen, 1984). Because Mississi pian ceramic vessels were capable of pro onged boiling (Braun, 1983, 19871, it would have been

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cooking at high on maize as a dietary staple and the use of ceramics capable of softenin hard foods would have tended to make t e Mississippian diet both less variable and softer than the Middle Woodland diet (Bullington, 1988).

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Dental materials Erupted teeth from the youngest individuals available were observed. Six months, the MATERIALS average age at eruption of the first human Archaeological sample deciduous teeth, constituted a logical lower Deciduous teeth were obtained from four age limit. Twenty-seven months of age was cemeter sites located in the lower Illinois chosen as an upper age limit to ensure that River J a l l y Three sites-Gibson, Pete observations were limited to microwear feaKlunk, and lizabeth-re resent the Middle tures on enamel, as dentin becomes widely Woodland period, which ates from ca. 50 BC exposed in these skeletal series past 27 to iu) 250 in this region (Farnsworth and months of age. Asch, 1986) and predates the local ado tion The individuals studied here could be aged of maize a iculture. Middle Woo!( land with relative precision using dental stangroups in the ower Illinois Valley engaged in dards of calcification and eruption (Thoma extensive horticulture. Their diet was char- and Goldman, 1960),which are closely assoacterized by an abundance of hard items, ciated with chronological age in very young including a variety of nuts and starchy seeds individuals (Ubelaker, 1978). In that variwith tough seed coats (Asch and Asch, ability in the timing of dental calcification 1985a-q 1986). Experiments in rocessing and eruption events is well documented (e.g., the hardest nuts and seeds in tRe Middle Garn et al., 1959), ste s were taken to miniWoodland diet (Murray and Sheehan, 1984; mize the potential e! f ect of inaccurate a e Talalay et al., 1984) indicate that they can- estimates: 1)Analysis was aimed at identi ynot be significantly softened without ro- ing age-related trends rather than exact longed boiling. Local Middle Woodlanb?ce- ages, 2) age categories for analysis were ramics. however. were ill-suited to. if not broad, 3) individuals with too few teeth preincapable of, sustaining prolonged 'boiling served to allow relatively accurate age esti(Braun, 1983, 1987). Thus the 20 Middle mates were excluded from the sample, as Woodland juveniles included in the present were individuals with obviously aberrant Sam le come from a human populatibn with eru tion and calcification patterns. a re atively hard diet (Bullington, 1988). TRe sample consisted of 36 individuals, for The Mississippian period, extending from each of whom a lateral incisor (maxillary or ca. AD 1000 to AD 1350 locally (Milner, 1984), mandibular) or a first mandibular molar was is re resented by 16 deciduous teeth from observed (Table 1).Incisors were observed the child site. That maize constituted a because the are the earliest teeth to erupt. dietary staple for Mississippian inhabitants Lateral rat er than central incisors were of the lower Illinois Valley is evidenced by used because they were less likely to have both archeobotanical remains (Asch and exposed dentin and, inex licably, were betAsch, 1985d) and carbon isotope ratios of ter preserved than centrafincisors. With few

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PREHISTORIC DECIDUOUS MICROWEAR

sample. In a pilot study, it was observed that the initial facets developing on cus tips tended to be more horizontally oriente than subsequently developed facets. Moreover, obliquely oriented cusp tip facets were char6 6.5-25.5 Incisors1 10 9.5-25.5 acterized almost exclusively by scratches, Molars2 10 10.5-24 10 12-25.5 whereas their horizontally oriented counterTotal 20 16 parts showed both scratches and pits. This Alateralincisor, either maxillary orrnandibular, was observed for difference in feature types suggested biomeeach of 10 infants in the sample without erupted deciduous molars chanical if not functional differences in mi(less t h a n ca. 12 months of age) and for each of six infants aged between 13 and 25.5 months. crowear formation between horizontally and 2Afirstmandibularmolarwasobservedforeachof20infantsaged obliquely oriented cusp tip facets (Gordon, between 10.5 and 25.5 months. 1982,1984a).Thus observations were made on either the cusp tip showing first microwear or, when facets were present, on the exce tions (Kelley, 1986; Ryan, 1981; most horizontally oriented facet. Teaird, 1983,1988; Walker, 19761, incisors have not been the subject of microwear analMETHODS sis because the anterior dentition is more Preparation of specimens for the scanning ikely to be used for nonmasticator activielectron microscopy (SEM) ties than is the posterior dentition. owever, The sample observed was composed of this is not a problem in a study seekin to document the onset and age-related deve op- both teeth and replicas. S ecimens were ment of earliest microwear, whatever its cleaned and replicated ollowing Rose (19831, with minor variations detailed elsesource. Observations on each incisor were limited where (Bullington, 1988). A majority of the to the incisal ed e and facets developed upon teeth in the sample had been preserved with it. Care was ta en not to include observa- a coatin of either Alvar 1520 or polyvinyl tions from the labial and lingual edges, acetate. 730th preservatives were satisfactowhich may differ functionally from one an- rily removed by ultrasonic cleaning of teeth other and from the incisal edge (Teaford, in acetone for a total of four minutes (two periods of 2 min duration). 1988). Molds were made of 3M Express (Light Molars were observed both because they are the traditional focus of microwear re- Body, Regular-Set; Type I, Low Viscosity). search and because incisors of older infants After de-gassing for a minimum of 36 hr, were usually devoid of incisal enamel. Cusp these molds were secured in 0 tosil 2 tip facets were chosen for observation, be- (Unitek Corporation), as described y Rose cause they were the consistent location of (1983) and sprayed with canned air to reearliest wear and facet development. Phase I move any incidental debris. Araladite (shearing) and Phase I1 (crushing) facets GY506 (Ciba-Geigy),a modified liquid epoxy were excluded from the sample because they resin, was used for all casting. It was mixed differ from cusp tip facets in both function in 50 ml containers with Ciba-Geigy Hard(Kay, 1977; Kay and Hiiemae, 1974) and ener HY956 and then syrin ed into the 3M microwear (Gordon, 1982, 1984a; Grine, molds. This epoxy was we 1 suited to the resent sample because of its low viscosity; it 1986; Teaford, 1985; Teaford and Walker, 1984). In this sample, ti s of two different !lowed into small cusps and cracks quite cusps showed evidence o earliest wear and easily, with a minimum of the bubbling artifacet development: the hypoconid and meta- facts often associated with the replication conid. For reasons discussed below, when process (Gordon, 1984b). Replicas and teeth were mounted with facets were present, only horizontally oriented tip facets were observed. On well-worn occlusal surfaces as parallel to the stub surteeth with facets on all cusps, the protoconid face as possible, following Gordon (1980) and tended to be the on1 cusp with a horizontally were allowed to de-gas for at least 24 hr prior oriented tip facet. hus some protoconid ob- to sputter coating. E ch specimen was sputter-coated with 600 of old alladium in a servations were also included. Efforts were made t o minimize potential Polaron 5100 Series f1 “8001” Sputter problems caused by using a mixed cusp tip Coater. TABLE 1. Sample by tooth type, culturalperiod, and age Middle Woodland Age range N (Months)

T

s

Mississippian Age range N (Months)

d

f:

P

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F

J

1

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J. BULLINGTON

Use of the SEM The SEM, a Cambridge Stereoscan 250, was operated at 20 kV, in secondary electron mode. All occlusal surfaces were positioned at an intermediate working distance of 25 mm. When it was necessarg to tilt a specimen to improve the image, t e tilt correction mechanism on the SEM was used to ensure comparable-sized fields of observation. A standard magnification of x500 was used. Selection of the precise site to be photographed and scored took place when a specimen was in the microsco e and after a preliminary scanning of t e entire occlusal surface. Two nonoverlapping micrographs were taken at each site. Data collection Features were qualitative1 categorized as either pits or scratches an then counted. ualitative observations of enamel surface c aracteristics were made by matchin enamel ap earance to categories develope during preEminar screening of the sample without knowle ge of age (Table 2; Fig. 1A-E). All scoring was done from micrograph slides. Because all fields of observation were of equal size, counts and frequencies of features are equivalent here, and both terms are used to refer to the data, which consist of numbers of features per field of observation. Feature size was not usually measured, but

f

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B

TABLE 2. Surface characteristics of deciduous molars and incisors at X5001 Stage I. On molars, cusp tip surfaces are rounded or conical; on incisors, they are rounded or undulating, depending on location of mammelons; enamel structure is very distinctly visible (Fig. 1A) Stage 11. Surfaces are as in Stage I. Enamel structure is becoming obscured but is still visible (Fig. 1B);this stage characterizes both molars and incisors Stage 111. Surfaces are flat and relatively smooth, showing only shallow microwear features; enamel structure is not visible (Fig. 1C); this stage characterizes both molars and incisors Stage IV. Surfaces are still visibly flat but are becoming intermittently abraded by deep microwear features; abraded and relatively smooth areas usually alternate within a single field; enamel structure is not visible (Fig. 1D);this stage characterizesonly molars Stage V. Surfaces are abraded and irregular throughout; enamel structure is not visible (Fig. 1E); this stage characterizes only molars 'These descriptions are based on SEM observations of the occlusal surfaces of human deciduous molars and incisors a t a working distance of 25 mm and a magnification of X500.

when categorization as a pit or scratch was doubtful, length and width measurements were made and the feature was cate orized on the basis of a 4:l length to widt ratio (Teaford, 1988). All micrographs were anal zed without knowledge of the age of the in ividual. Each micrograph was scored for feature frequency by this observer on three separate occasions. For each micrograph, the following scores were obtained: total feature frequency, pit frequency, scratch frequency, and pit to scratch ratio. Total feature frequency scores were relatively stron ly positively correlated for the three sets of o servations (Table 3). Criteria used for scoring surface characteristics are presented in Table 2 and should be read in conjunction with Figure 1A-E. Each micrograph was scored twice for surface characteristics. The two surface characteristic scores per micrograph were highly correlated (Kendall's 7 = 0.879). Formation of subsamples Three different criteria are used to form age-group subsamples: 1)individual age, 2) erupted a e of a tooth, and 3) presence or absence o a wear facet. To investigate microwear differences between juveniles on the basis of individual age, the sample is first divided into two age groups: individuals 4 months. The unavoidable error inherent in both estimates of age and erupted age makes it desirable to have another criterion for subdividing the sample into age groups: presence or absence of a wear facet (incisal or cusp tip). This trait was scored during data collection without knowled e of age or eru ted age. analye dif erences between cultural groups, a1 Middle Woodland teeth (molars and incisors combined) are grouped for comparison with all Mississippian teeth. To exlore differences between tooth types, all ratera1 incisors (mandibular and maxillary)

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PREHISTORIC DECIDUOUS MICROWEAR

Fig. 1. Five stages of enamel surface characteristics; see Table 2 for full description of these stages. Teeth were assigned t o surface characteristics stages to determine whether differing surfaces were associated with differences in diet or with duration of exposure to wear. In this sample, surface characteristics were strongly associated with exposure to wear and tooth type. A Stage 1.Deciduous lateral mandibular incisor. The few

63

features present are scratches. B: Stage 11. Deciduous lateral maxillary incisor. Most features are scratches. C: Stage 111. Deciduous first mandibular molar. Both scratches and its are present. D: Stage IV. Deciduous first mandibukr molar. Both scratches and pits are present; its predominate. E: Stage V. Deciduous first mandibufar molar. Most features are pits.

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J. BULLINGTON

TABLE 3. Correlations between three separate total feature counts of 72 micrographs by a single observer Count 1 Count 1 Count 2 Count 3

0.81* 0.58*

Count 2

Count 3

-

-

0.77*

and intercepts of regression lines may be compared using this method. The former comparison provides insight into differences in rates of feature frequency change, the latter into differences in feature frequencies at earliest ages or stages of wear.

*P < 0.05.

RESULTS

are grouped for comparison with molars. In analyses of age-related trends characterizing the sample as a whole, molars and incisors from both cultural groups are combined. Statistical methods All statistical analyses were erformed with Systat (Wilkinson, 1987). orrelation coefficients serve to identify associationsbetween feature frequencies and age variables. Feature frequenciesfor subsamples are compared using Student’s t tests. Qualitative surface characteristics data are considered ordinal in nature and are compared between subsamples using the Kolmogorov-Smirnov two-sampletest. Model I re ession is used to analyze agerelated tren s in feature frequency within the sample as a whole and within subsamples. Each feature frequency variable is regressed separate1 on age and on erupted age. Because ana ysis of a pilot subsample revealed that feature frequency increased with age, one-tailed tests were deemed appropriate for re ession analyses. Comparison of rates of eature frequency change in various subdivisionsof the Sam le are made using multiple regression with ummy variables (Bohrnstedt and Knoke, 1985). This method permits the incorporation of categorical variables such as tooth t pe or cultural group into the regression moc! el. Both slopes

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Feature frequency The sample as a whole. Statistical significance is measured at the .05 level throughout. Results of regression analyses, presented in Table 4, show that all feature frequency variables except pit scratch ratio increase with age andor eru ted age. Dummy regression is use to test for differences in slope and intercept between different feature types regressed on age variables. Slope comparisons show that scratch frequency increases significantly more rapidly than pit frequency with erupted age (Fi .2). Intercept comparisons show that at ear iest ages and stages of wear, scratch frequencies are significantlyhigher than pit frequencies (Figs. 2,3). Age groups. Student’s t tests show that older individuals have higher total feature and pit frequencies than younger individuals (Table 5 ) . These comparisons are not confounded by tooth type, in that there is no significant association between tooth type and these age group subsamples (Yates’corrected x2 = 2.78; P = 0.10; d.f. = 1). Erupted age grou s (teeth erupted ~4 months and 14 mont s) differ significantly for total feature frequenc , pit frequency, and pit scratch ratio (Tab e 6). There is no significant association between the erupted age subsamples and tooth ty e (Yates’ corrected x2 = 0.45;P = 0.50; d!. = 1). Facet-based subdivisions corroborate results based on comparisons of 1) individ-

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TABLE 4 . Results of regression of four measures of feature frequency on two measures of age for a sample of 36 molars and incisors’

X

Y

Age Age Age Age Erage Erage Erage Erage

Count Scratch Pit P/S Count Scratch Pit P/S

Intercept (a)

Slope (b)

S.E. b

R2

P2

10.51 14.31 -3.89 -0.20 28.43 20.58 3.08 0.28

1.83 0.93 0.55 0.04 1.81 1.42 0.25 0.01

0.58 0.60 0.23 0.03 0.64 0.63 0.26 0.03

0.21 0.06 0.14 0.04 0.18 0.12 0.03 0.00

0.00 0.07 0.01 0.10 0.00 0.02 0.17 0.36

l I n this and all following tables, Age = individual age, Erage = erupted age, Count = total feature frequency, Scratch = scratch frequency, Pit = pit frequency, P/S = pit scratch ratio. 20ne-sided probability that slope (b)differs from zero.

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PREHISTORIC DECIDUOUS MICROWEAR 80

701 60

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8 0

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16

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20

Erupted A ge (in m o n t h s ) Pit + Scratch

Fig. 2. Scratch (up er line) and pit (lower line) counts regressed on erupted age. Slopes and intercepts differ signif!cantly.

uals4 positively corremonths. Teeth wit facets have significantly erupted age. In higher total feature frequencies and pit fre- incisors, total feature fre uency and scratch uencies than teeth without wear facets frequency are significant y positively corre&able 7). Analyses based on presence or lated with age, whereas only scratch freabsence of a facet are not confounded by quency is significantly correlated with tooth type, in that the presence or absence of erupted age. a facet is not significantly associated with Dummy regression is used to test for diftooth type in this sample (Yates’ corrected ferences in patterns of age-related chan es x2 = 2.81; P = 0.09; d.f. = 1). between molar and incisor subsamp es. Incisors and molars. Incisor (n = 16) and There are no slope differences between tooth molar (n = 20) subsamples differ signifi- types for any feature frequency variable recantly for mean individual a e, pit freessed on eru ted age. A majority of tests uency, and pit scratch ratio (Ta le 8). They Kr intercept ifferences between incisors %o not differ for mean erupted age, total and molars are statistically significant, sugfeature frequency, or scratch frequency. esting that pit and scratch frequencies are Comparisons of microwear development in iifferent in the two tooth types at the earliest molars and incisors focus on erupted age in stage of wear. Only regressions for total order to control for differences in individual feature frequency show no significant differage between tooth ty e subsamples. Analy- ences in intercept. ses of microwear deve opment within incisor Cultural groups. Middle Woodland and and molar subsamples consider both age and Mississippian juveniles are compared to deerupted age. Within the molar subsample, termine whether dietary differences are re-

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J. BULLINGTON 80

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20

Age (in months) + Scratch

Fig. 3. Scratch (upper line) and pit (lower line) counts regressed on age. Intercepts differ significantly; slopes do not.

TABLE 5. Student's t tests for differences in feature frequencies between younger (N = 18) and older (N = 18) age groups in a combined sample of molars and incisors'

Feature Count Scratch

Pit PIS

Feature frequency per field of observation2 4 months S.D. Mean S.D. Mean

0.01 0.10 0.01 0.04

Count Scratch Pit P/S

33.83 26.33 1.61 0.07

21.65 18.59 2.73 0.13

47.11 33.17 7.83 0.66

P

12.89 18.62 9.51 1.19

0.02 0.14 0.00 0.02

'I values reported here are one-sided. 'A11 fields of observation of equal size,

'I' values reported here are one-sided. 2A11 fields of observation of equal size.

flected in differences in onset and earliest development of juvenile microwear. Comparisons between cultural groups are not confounded by tooth type, as there is not a statistically significant association between cultural group affiliation and tooth type (Yates' corrected x2 = 0.89; P = 0.37; d.f. = 1).

Student's t tests show no statistically si nificant differences between Middle Woo land and Mississippian subsamples for age, erupted a e, or any of the feature fre uenc variables ?Table 9). Within the Middle 00 land subsample, regression analyses show no significant relationship between any feature frequency variable and either age vari-

8

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PREHISTORIC DECIDUOUS MICROWEAR

able; moreover, no feature fre uency variables are significantly correlate with either age or eru ted age. Regression anal ses within the ississippian subsample s ow Feature frequency per field that a number of feature frequency variables of observation2 increase with age and/or erupted a e Facet absent Facet present (Table 10). Within the Mississippian su Feature Mean S.D. Mean S.D. P sample, there are also significant positive correlations between age and total feature 0.00 19.45 3.89 2.56 11.09 Age 8.85 4.29 0.00 Erage 2.19 1.97 frequenc (r = 0.67) and between erupted Count 31.38 47.55 13.14 0.00 23.90 age a n 8 both total feature frequency 36.50 19.35 0.10 Scratch 27.19 22.09 (r = 0.65) and scratch frequency (r = 0.51). 6.6 8.89 0.01 0.88 2.47 Pit Dummy regression shows no significant P/S 0.02 0.08 0.45 0.96 0.05 differences in slope between the cultural lUnits of measurement for age variables (Age, Erage) are months subsamples for any feature frequency variin this and following tables. 2A11 fields of observation of equal size. able. Intercepts differ significantly only for total feature frequency regressed on age (Fig. 4). At very early ages, total feature frequencies are higher for Middle Woodland than Mississip ian teeth. All erupted teeth in the sample s ow microwear, regardless of the age or cultural affiliation of the individTABLE 8. Student’s t tests for differences in ages and ual. feature frequencies between molars (N = 20) and incisors (N = 16)’ Surface characteristics Feature frequency per field Surface characteristics scores are signifiof observation2 cantly positively correlated with age Incisors Molars (r = 0.44), erupted age (r = 0.411, total feaFeature Mean S.D. Mean S.D. P ture frequenc (r = 0.28), pit frequency (r = 0.69), an pit scratch ratio (r = 0.65). 17.58 4.28 5.81 0.04 Age 13.89 5.78 4.21 Erage 6.00 5.43 0.89 Kolmogorov-Smirnovtwo-sample tests show Count 40.33 23.01 40.39 17.44 0.99 significant differences for surface characterScratch 37.83 26.89 15.47 0.12 24.32 istics between older and younger age groups 7.67 9.10 Pit 0.44 0.62 0.00 (P < 0.001), erupted age groups (P < 0.001), 0.52 1.00 P/S 0.01 0.01 0.04 and teeth with and without facets values reported here are two-sided. (P < 0.001). Analysis of variance using the 2A11 fields of observation of equal size. five surface categories to compare means of feature fre uency variables show significant differences etween surface categories for all such variables. Kolmogorov-Smirnov two-sample tests show significant differences for surface charTABLE 9. Student’s t tests for differences in ages and acteristics between molar and incisor subfeature frequencies between Middle Woodland (N = 20) samples (P < 0.001). Molars exhibit all five and Mississippian (N = 16) juveniles in a combined surface characteristic categories, whereas sample of molars and incisors1 incisors exhibit only the first three. There Feature frequency per field are no significant differences for surface of observation2 characteristics between Middle Woodland Middle and Mississippian subsamples. Woodland Mississippian TABLE 7. Student’s t tests for differences in ages and feature frequencies between teeth with (N = 20) and without (N = 16) wear facets in a combined sample of molars and incisors1

!

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E

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~

1

Feature Age Erage Count Scratch Pit P/S

Mean 14.52 4.83 41.19 29.81 4.33 0.30

S.D. 4.91 4.27 20.05 29.35 8.32 0.87

Mean 16.77 6.47 35.18 26.88 4.65 0.39

IP values reported here are two-sided. zAll fields of observation of equal size.

S.D. 5.69 5.18 20.43 18.97 6.47 0.88

P 0.20 0.29 0.37 0.64 0.90 0.76

DISCUSSION

Feature frequency The sample as a whole. Analysis of the sample as a whole reveals that total feature frequency increases with both age and erupted age. Gordon (1982,1984a) reported the opposite trend in a sample of permanent chimpanzee teeth. She suggested that this

68

J. BULLINGTON

TABLE 10. Results of regression offourmeasures of feature frequency on two measures of age for a combined sample of molars and incisors of Mississippian juveniles (N = 16)

Intercept (a)

X

Y

Age Age Age Age Erage Erage Erage Erage

Count Scratch Pit PIS Count Scratch Pit P/S

-5.05 3.80 -3.24 -0.08 18.47 14.73 2.86 0.34

P'

Slope (b)

S.E. b

R2

2.39 1.38 0.47 0.03 2.58 1.88 0.28 0.01

0.69 0.78 0.27 0.04 0.77 0.81 0.32 0.04

0.45 0.17 0.17 0.03 0.43 0.26 0.05 0.00

0.00 0.04 0.04 0.24 0.00 0.02 0.20 0.42

IOne-sided probability that slope (b) differs from zero.

80

70

I

50

1

0

0

0

-1

a,

0 1 0

I

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4

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r , m

' 1 -

- 1

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12

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Age (in months)

0

Middle Woodland

I

15

I

I

20

+

I

I

24

I

28

Mississippian

Fig. 4. Total feature count regressed on age for Middle Woodland (upper line) and Mississippian (lower line) infants. Intercepts differ significantly; slopes do not.

age-related decrease in feature frequency might be attributable either to the erasure of features as a tooth surface is reworked or to differences in hardness between surface and subsurface enamel (Gordon, 1982:212). Gordon's results and those presented here appear complementary rather than contradictory: they reflect trends in total feature frequency characteristic of different age

groups. Stud of a sample with a broad age range shoul show an initial increase in feature fre uency followed by a decrease. Scratch requency increases more rapidly with erupted age than does it fre uency. Although it is possible that tiis digerence reflects an actual difference in the rates at which the two different feature types are produced, differences in feature size provide

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an alternative explanation. Because feature size was not enerally measured, it must be borne in min that the following explanation is based on qualitative observations and characterizations. Pits in this sample are generally much larger than scratches. When a surface is heavil pitted, it is usually covered by a relative y small number of large its rather than a large number of small pits. &hisis not the case with scratches, however. Heavily scratched surfaces usually contain a large number of small (thin)scratches. Thus, heavily scratched surfaces have higher feature frequencies than heavily pitted surfaces. The seeming difference in rates of accumulationmay simply reflect differences in feature size and the fact that the upper limit for scratch frequency is higher than that for pit frequency. It may also reflect, to some extent, the difficulties encountered in identifyin individual pits on heavily pitted surfaces ( eaford, 1988). Intercepts are significantly different for feature type regressed on both age and erupted age: in the earliest stages of wear, scratch frequencies are higher than pit frequencies. Differences in feature size should not confound this result; at the earliest stages of wear, feature frequenciesare so low that feature size is not a limiting factor. Age groups. Comparisons of feature frequencies between younger and older age groups (and between less: and more worn teeth) yield rather consistent results, regardless of the criteria used for defining the groups com ared. In all comparisons, older teeth have igher total feature frequencies than younger teeth. Pit frequencies and it scratch ratios are also higher for 01 er individualskeeth. Scratch frequency, however, does not differ between age This result may appear paradoxica when compared to regression results showing that scratch frequency increases with erupted age and increases more rapidly than pit frequency with erupted age. This seeming paradox may be an artifact of small sample size: regressions were run on a sample of 36 teeth, whereas age groups compared contained only 18 teeth each. The fact that the sample was arbitrarily divided into age and erupted age groups of equal sizes, without taking developmental criteria into account, may also be partially responsible for the failure of a e group comparisonsto reflect an age-relate trend characterizing the sample as whole. Thus, in this sample, pit frequency and

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proportion of pits both appear to have strong relationships to a e and exposure to wear, whereas scratch requency does not. This suggests that relatively hard items producing pits were consumed only by older ‘uveniles. It is also possible that the age-re ated trends in pitting in this sample could be the cumulative result of continued ex osure to hard items rather than a simple re ection of differing diets for younger and older individuals. Given the ra idity of microwear turnover (Teaford and yen, 19891,this explanation seems less likely than that proposing age-related differences within juvenile diet. Incisors and molars. Com arisons between molars and incisors in dpicate significant differences for pit frequency and pit scratch ratio, but not for total feature frequency or scratch frequenc . Comparisons of regression slopes for mo ars and incisors reveal no significant differences in the rates at which any feature frequency variable increases. However, there are significant interce t differences between molars and incisors or scratch frequency, it frequency, and pit scratch ratio regresse on both age and eru ted age. These differences suggest that ear iest wear in incisors is characterized by higher scratch frequencies than that in molars, whereas earliest wear in molars is characterized by higher it frequencies and pit scratch ratios than t at in incisors. These differences between molars and incisors made biomechanical sense in terms of microwear formation: the high bite forces necessary for crushing hard objects (and producing pits) characterize the posterior rather than anterior dentition. Observation of cusp tip facets should not have biased this comparison. The cusp tip, which is characterized by both pits and scratches, is considered to have microwear “intermediate” between that observed on crushing and shearing molar facets, which are characterized, respectively, by preponderances of pits and scratches (Gordon, 1982). Finally, it should be noted that because ex loratory use of the mouth by juveniles in t e age range studied here is not limited to the anterior dentition, it is also ossible that teethingrelated wear on bot molars and incisors may have obscured functional differences to some extent. Cultural groups. All erupted teeth in the sample show microwear, regardless of the age or cultural affiliation of the individual. Differences in diet do not appear to be reflected in the timing of the appearance of the

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earliest microwear, which is most probably produced at least in part by teething activities. On the basis of age at earliest appearance of microwear alone, it is not possible to distinguish between Middle Woodland and Mississippianjuveniles or their diets. Nonetheless, microwear analysjs does provide some insight into the weaning diets characterizing these two cultures, In the Middle Woodland sample, no feature frequency variable shows a significant relationship to any age variable. In the Mississip ian sample, total feature frequency, scratc frequency, and it frequency show significant increases wit age; total feature frequency and scratch frequency show significant increases with erupted a e. Moreover, comparisons of Middle Woo and and Mississip ian regressions show significantly di ferent intercepts for total feature fre uency regressed on age (Fig. 4).At very ear y ages, total feature frequencies are higher for Middle Woodland than Mississippian teeth. Experimental data on the microwear correlates of hard and soft diets provide an explanation for this difference in intercepts. Molars of animals on soft diets ma have fewer features that molars of animars on hard diets (Teaford, 1988). Applied here, this suggests that very young Mississippian children were probably consuming a Middle Woodland consistent with

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thermore, the absence of a relationship between any feature frequency variable and age variable within the Middle Woodland sample suggests that during this eriod supplemental diet was quite varia le andlor introduced to juveniles at varied ages. The decreased dietary variability characterizing Mississippian juveniles could reflect both the reliance on a dietary staple and the existence of food processingtechnology capable of producing a softened juvenile diet of relatively homogeneous texture. Surface characteristics The five surface characteristic stages described in Table 1 and illustrated in Figure 1A-E are stron ly correlated with age, erupted age and a1 feature frequency variables except scratch frequency. Moreover, surface characteristics differ significantly between older and younger age groups, however defined,

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Molars and incisors differ for surface characteristics. Molar cusp tips in this sample exhibit all five of the surface characteristic categories, whereas incisal ed e surfaces do not progress past Stage 111. he heav pitting that characterizes Stages IV an V is not observed on incisors. This is not surprising, given that heavy pitting is generally associated with crushinglgrinding and has rarely been reported on incisors. Moreover, age differences between the molar and incisor samples probably also contribute to this pattern, in that the molar subsample comes from significantly older individuals. Middle Woodland and Mississippian samles do not differ for surface characteristics. ;plhis is of some interest; Middle Woodland and Mississippian diets might have been expected to produce different qualitative microwave signatures such as those identified by Rose and associates (Blauer and Rose, 1982;Harmon and Rose, 1988; Marks et al., 1985;Moore-Jansen et al., 1980;Rose, 1984; Rose and Harmon, 1986; Rose and Marks, 1985; Rose et al., 1979, 1981, 1983) in the permanent dentitions of a variety of prehistoric skeletal series. Instead, qualitative surface characteristics are strongly related to age and duration of exposure to wear, not to cultural period or subsistence. Several alternative explanations can be offered for the fact that such characteristic group patterns are not identifiable in this sample. First, it is possible that despite clear archeological evidence of dietary differences between these groups, such differences characterized adult rather than juvenile diet. That is, whatever the available dietary components and food processin techniques, weanling foods were invariab y so softened that they would not roduce microwear patterns reflective o f t e relative hardness of the adult diet. Second, it is possible that there were in fact differences between 'uvenile diets which were masked b teet ingrelated wear. Third, it is possib e that the deciduous enamel of recently erupted teeth, which is thinner (Wheeler, 1965) and more porous (Fearnhead et al., 1982)than permanent enamel, wears in a way that obscures dietar differences. Fourth, it is possible that t e microwear observed does in fact reflect dietary differences that were simply not detected because metric data on feature size were not collected and analyzed. Fifth, it is possible that the variability of the Middle Woodland weanling diet and the homogeneity of the Mississippian weanling diet ren-

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dered it im ossible to detect differences be- surfaces do not display the last two stages, tween sucff small samples. Sixth, it is which are characterized by relatively heavy possible that age-related differences be- pitting. These differences make biomechanitween diets for younger and older children cal sense, in that the high bite forces neceswithin both cultural roups rendered it im- sary to crush hard objects and produce pits possible to distinguis differences between characterize molars rather than incisors. cultural groups. Finally, it is possible but Middle Woodland and Mississippian juveunlikely that weaning in both groups oc- niles could not be distinguished on the basis curred so late that the microwear observed of enamel surface characteristics. Age-rehere is entirely unrelated to diet. lated chan es in surface characteristics Data are not currently available to evaluate cross-cut cu tural boundaries. This suggests all these possibilities. The present analysis that within both groups there were different lends greatest support to those explanations diets for younger and older juveniles. Age pro osing age-related dietary differences and duration of exposure to wear impact wit in cultural groups and differences in the juvenile microwear and should be taken into physical consistency and variability of juve- account when using the deciduous dentition to explore archaeological diet. nile diet between cultural groups.

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CONCLUSIONS

ACKNOWLEDGMENTS

In analysis of a sample composed of two different cultural groups, frequencies of microwear features increase with age and exposure to wear in the deciduous teeth of juveniles less than 27 months of age. This increase in feature frequency characterizes the Sam le as a whole, age-group subsamples, mo ar and incisor subsamples, and the Mississippian subsample. Age-related decreases in feature frequency (Gordon, 1980, 1982)seemingly characterize older individuals and/or the ermanent dentition. Study of a sample wit a broader age range than either Gordon’s or that utilized here should establish that these age-related trends in microwear feature frequency are complementary. Age at first appearance of microwear does not vary by cultural group. All eru ted teeth show microwear features, regard ess of the age or cultural affiliation of the individual. Earliest wear is most robably produced by teething activities; dif erences in diet do not appear to affect age a t first appearance of microwear. This does not mean, of course, that a e at introduction of solid food may not have fiffered between these two groups but only that it could not be detected by identifying age at first appearance of microwear. Comparisons of age-related microwear trends between Middle Woodland and Mississippian juveniles suggests that the Mississippian juvenile diet was softer and less varied in physical consistency than the Middle Woodland juvenile diet. Microwear patterns fell into five qualitative stages that are strongly correlated with both age and erupted age. Molar cusp tips display all five wear stages; incisal edge

I thank Jane E. Buikstra and Della C. Cook for access to dental material under their care, and I am most grateful to members of my dissertation committee, Jane E. Buikstra, Mark F. Teaford, and Malcolm Dow for their advice. I also thank Alan Walker and Pat Shipman for their help during the early stages of this research and Ed Furia for his he1 during the later stages. I am grateful to teve Leigh for his support and advice throughout this research and to three anonymous reviewers for their constructive comments. This research was supported by NSF doctoral dissertation improvement grant BNS 8515376 to the author and Jane Buikstra. The SEM used for this research was purchased for the Indiana University Biology Department with NSF grant PCM 8212660.

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