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The isotopic compostition of human diets in prehistoric southeastern Texas.

ABSTRACT. -- Stable carbon isotope ([[delta].sup.13]C) analysis of human skeletal remains from the Ernest Witte archaeological site (41AU36) in southeastern Texas indicated that this Late Archaic population consumed food items derived largely from the [C.sub.3] plant portion of the food web. Despite the fact that this hunter-gatherer group lived in a coastal prairie ecosystem dominated by [C.sub.4] grass species, less than 20 percent of their diet was derived from this portion of the food web. When these results are coupled with other cultural and contextual information from the region, it appears that this population subsisted on a stable terrestrial resource base centered on [C.sub.3] resources, mainly nuts and deer. It is hypothesized that the [C.sub.4] dietary component is comprised of lower trophic level foods that required increased energy to harvest and process, and as such represent an intensification of production that is a component of increasing complexity in hunter-gatherer societies. Key words: stable carbon isotopes; human diets; late Archaic and Woodland periods; southeastern Texas.

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The analysis of stable carbon isotope ratios ([.sup.13]C/[.sup.12]C, or [[delta].sup.13]C) from bone collagen preserved in prehistoric sites has given archaeologists a direct chemical method for the study of human dietary patterns. Controlled laboratory studies of animals maintained on monotonous diets have demonstrated the correlation between the stable carbon isotope ratios of their tissues and their diet (DeNiro and Epstein, 1978; Tiezen et al., 1983). Stable carbon isotope ratios of bone collagen and other preserved tissues have been used to assess the relative proportion of [C.sub.3] and [C.sub.4] plants in terrestrial-based human (Vogel and van der Merwe, 1977; Bender et al., 1981; Boutton et al., 1984; Schwarcz et al., 1985) and animal diets (Vogel, 1978; Chisholm et al., 1986; Ambrose and DeNiro, 1986; Huebner and Boutton 1990). Marine components in human diets can also be identified with stable carbon isotopes (Tauber 1981; Chisholm et al., 1982) although, this can be problematic if [C.sub.4] or Crassulacean Acid Metabolism (CAM) plants are present in the dietary environment.

Three different photosynthetic pathway types have been recognized among terrestrial plants, which have biochemical anatomical, physiological, and ecological differences. Furthermore, the different photosynthetic pathway types have unique [[delta].sup.13]C ratios resulting from carbon isotope fractionation during C[O.sub.2] fixation. Plants with the [C.sub.4] photosynthetic pathway include primarily warm-season grasses of tropical and subtropical origin, and some dicotyledonous weeds that thrive in warm, arid or semiarid regions. These plants discriminate the least against atmospheric [.sup.13]C[O.sub.2] ([[delta].sup.13]C = -8 permil) giving them an average [[delta].sup.13]C of -12.5 permil. [C.sub.3] plants, which include trees, shrubs and most herbaceous dicots, discriminate more against [.sup.13]C[O.sub.2] and have an average [[delta].sup.13]C value of -26.5 permil (Smith and Epstein, 1971). Nearly all grass species in southeastern Texas are [C.sub.4], whereas woody species and forbs in this region are [C.sub.3] species. CAM plants are primarily desert succulents with the ability to use [C.sub.3] or [C.sub.4] photosynthetic pathways, and are not common in the humid environment of southeastern Texas.

During metabolic synthesis, carbon isotopes from dietary sources may be fractionated slightly as they are incorporated into biochemical fractions and tissues (DeNiro and Epstein, 1978; Lyon and Baster, 1978; Tieszen et al., 1983). Bone collagen in large herbivores and humans is enriched by approximately +5 permil relative to diet (Krueger and Sullivan, 1984). Thus, bone collagen of an animal on a pure [C.sub.4] plant diet would have a [[delta].sup.13]C = -7.5 permil, whereas that of an animal on a pure [C.sub.3] diet would have a [[delta].sup.13]C = -21.5 permil.

The purpose of this study was to test the hypothesis that Late Archaic populations living in mixed [C.sub.3]-[C.sub.4] plant communities in southeastern Texas subsisted on a stable terrestrial resource base centered on nuts and deer.

SAMPLE ENVIRONMENT

The sample group for this study was from the Ernest Witte site (41AU36) located in southeastern Austin County, Texas. This site is located on a bluff overlooking the floodplain of the Brazos River (Fig. 1). Four temporally discrete burial groups were identified in this large mortuary site, which spans the period ca. 4700 - 1000 BP (Hall, 1981). The 10 human samples used in this study were derived from the Late Archaic Period Burial Group 2 (ca. 2400 - 1500 BP). This group included at least 145 individuals, the majority of which were found in extended supine positions with their heads oriented northeastward. A single dog interment recovered from the stratigraphic zone directly above this human burial population is included in the sample.

Although paleoenvironments of this region are not well understood, early historic documents characterized the prairie uplands around the site as dominated by tall grasses with the [C.sub.4] pathway, broken by occasional motts of trees with the [C.sub.3] pathway (Hall, 1981). This essentially modern regional pattern of biota was established by approximately 2500 BP (Story, 1985). Dominant plants included the grasses little bluestem (Schizachyrium scoparium) and Indiangrass (Sorghastrum nutans) on clays, and various oaks (Quercus stellata and Q. marilandica) and hickory (Carya sp.) on sands. Riparian communities were dominated by [C.sub.3] plants and included cedar elm (Ulmus crassifolia), Texas sugarberry (Celtis laevigata), and pecan (Carya illinoiensis). Thus, human food webs in this region were based on a combination of [C.sub.3] and [C.sub.4] plant resources.

[FIGURE 1 OMITTED]

Terrestrial mammals found commonly in Late Archaic sites in this region include white-tailed deer (Odocoileus virginianus), eastern cottontail (Sylvilagus floridanus), and pocket gopher (Geomys sp.), although the latter may not have been of economic importance. Fish such as fresh water drum (Aplodinotus grunniens) and land turtles (Terepene sp.) also are present in these sites, as are freshwater molluscs including Lampsilis sp., Ligumia subrostrata, and Amblema plicata perplicata (Lord, 1981). Marine species such as the lightning whelk (Busycon sp.), the shell of which often are seen in the form of pendants and beads in the grave goods associated with Burial Group 2, also may have served as a food source.

METHODS

Bone samples were cleaned manually and ultrasonically in distilled water, then powdered in a Wiley mill to pass a 20-mesh screen. Collagen was extracted following the method of Boutton et al. (1984) using a 0.1 N HCI pretreatment for six hours to remove carbonates followed by a 0.1 N NaOH soak for 12 hours to remove soil humates. Collagen then was solubilized from the bone by incubation in distilled water at pH 3 at 90[degrees]C for 24 hours with occasional stirring. Carbon in the collagen then was converted to C[O.sub.2] by combustion in the presence of 2g [C.sub.u]O in an evacuated, sealed quartz tube at 900[degrees]C for two hours (Boutton et al., 1983). Isotope ratios were measured on the resulting C[O.sub.2] with a VG-903 (Middlewich, UK) dual inlet, triple collector isotope ratio mass spectrometer and the results are reported using the [delta] notation relative to the international PDB standard in permil (percent):

[[delta].sup.13]C ([per thousand]) = [[[([.sup.13]C/[.sup.12]C) sample]/[([.sup.13]C/[.sup.12]C) standard]] - 1] X 1000.

Analytical precision (machine error plus sample preparation error) for bone collagen [[delta].sup.13]C was [+ or -] 0.1 permil.

RESULTS

Results of the stable carbon isotope analyses are shown in Table 1. The sample consisting of seven males and three females have an average [[delta].sup.13]C of -19.2 [+ or -] 0.70 permil. No sex effect (cf. Lovell et al., 1986) was seen as the isotopic difference between the sexes was not significant (M [[delta].sup.13]C = -19.4 permil; F [[delta].sup.13]C = -18.8 permil). There was also no significant isotopic difference between those individuals intered with grave goods ([[delta].sup.13]C = -19.0 permil) and those without ([[delta].sup.13]C = -19.5 permil). The collagen from the single dog burial had a [[delta].sup.13]C value of -20.7 permil, which is 1.5 permil more depleted than the human average.

The human isotopic values indicate a dietary pattern with heavy reliance on [C.sub.3] plants, and animals that consumed [C.sub.3] plants. The percentage of [C.sub.3] plants in the diet can be estimated from the mass balance equation:

percent [C.sub.3] in diet = [[[delta].sup.13]C - 5 + 12.5]/[-26.5 - (-12.5)].

This equation uses averages of [C.sub.3] and [C.sub.4] plant [[delta].sup.13]C values, and cannot account for the actual isotopic values of foods consumed. Allowing for this, and the precision of isotopic determinations ([+ or -] 0.1 permil), the precision of this estimate of [C.sub.3] derived foods in the diet is [+ or -] 8 percent (Schwarcz et al., 1985). Thus the percentage of [C.sub.3] foods in the Ernest Witte human diet is 83.6 [+ or -] 8 percent.

DISCUSSION

Approximately 85 percent of human diet during the Late Archaic at the Ernest Witte site was derived from the [C.sub.3] portion of the resource base. To account for the remaining 15 percent of the diet, three possibilities exist: (1) humans may have consumed [C.sub.4] plant material directly in the form of grass seeds; (2) humans may have consumed animals, terrestrial or freshwater, which derived some portion of their diet from [C.sub.4] plants; or (3) humans may have consumed marine vertebrates and invertebrates, which are known to have [[delta].sup.13]C ratios intermediate to [C.sub.3] and [C.sub.4] plants.

It is possible that one or more of these subsistence options were practiced by the people who buried their dead at this site. However, the first two seem the most plausible given the archaeological evidence from this and nearby sites. Within 40 kilometers of the Ernest Witte site are five other cemeteries of equivalent age (Highley et al., 1988). The density of these sites in the Colorado and Brazos drainages 100 to 160 kilometers from the coast, and the absence of similar sites near the mouths of these rivers on the Gulf Coast, suggests that terrestrial food sources were more important than marine sources.

Unfortunately the only isotopic data for species of prehistoric economic importance in this region are for whitetailed deer and acorns. Deer bone collagen had an average [[delta].sup.13]C of -21.2[+ or -]1.79 permil for modern samples from central Texas (Land et al., 1980). Acorn fragments recovered from a pit beneath a large burned rock midden (41BN63) in Bandera County dated to 4220[+ or -]390 BP (TX7066) had a [[delta].sup.13]C of -26.8 permil (Thomas R. Hester, personal comunication). Thus it is difficult to do more than speculate concerning the actural terrestrial [.sup.13]C-enriched dietary compontents. However, the isotopic data from the Ernest Witte humans do support Hall's (1992) subsistence hypothesis. Hall has argued that the large cemeteries found in the lower Brazos and Colorado river valleys were a product of a subsistence economy based on a rich, reliable, non-mobile food stuffs: acorns and nuts, in particular, pecan, hickory and walnuts. These nut-bearing trees were, and still are, found commonly in riparian zones as were deer which, based on faunal remains (Lord, 1981), were the primary meat source of these people. A diet comprised largely of these [C.sub.3] foods is supported by the human isotope values.

Although the dietary pattern identified at the Ernest Witte site was based heavily on [C.sub.3] pathway food stuffs, the [[delta].sup.13]C ratios are more enriched than most other Late Archaic or Woodland diets elsewhere in North America. Four samples from Archaic and Early Woodland contexts (4500-2100 BP) in New York reported by Vogel and Van der Merwe (1977) had an average [[delta].sup.13]C of -19.7[+ or -]1.13 permil. From six sites in Illinois, Ohio, and West Virginia, 31 Archaic and Woodland samples had an average [[delta].sup.13]C of -21.4[+ or -]0.78 permil (Van der Merwe and Vogel, 1978). In a study to determine the importance of maize in Hopewell diets, Bender et al. (1981) analyzed five individuals from the Archaic Reigh site (ca. 2700 BP) in Wisconsin and 19 individuals from five Middle Woodland Hopewell sites (2100-1600 BP) in Michigan, Illinois, and Ohio. The mean from the Hopewell samples, -21.9[+ or -]1.01 permil agrees with the Archaic mean, -22.0[+ or -]0.65 permil and indicates that maize was not an important component in Hopewell diet. Schwarcz et al. (1985) analyzed three human samples from a single Archaic site, and 15 samples from five Middle Woodland sites in Ontario, Canada. Their results were consistent with those from the northeastern and midwestern United States; mean [[delta].sup.13]C for the Archaic group was -20.8[+ or -]1.40 permil, and -20.8[+ or -]1.22 permil for the Middle Woodland population. In a study to identify the introduction of maize into the Ozark Highlands and Mississippi River Valley of eastern Missouri and Arkansas, Lynott et al. (1986) analyzed 10 individuals from eight premaize sites. The mean [[delta].sup.13]C ratio of three Late Archaic (5200-3000 BP) samples was -21.1[+ or -]0.6 permil, four Woodland (2300-1000 BP) samples -21.0[+ or -]0.4 permil, and three Big Lake Phase Mississippian (1100 BP) samples -20.6[+ or -]0.81 permil.

The isotopic separation of the Ernest Witte sample from these other Archaic and Woodland samples may not indicate a different diet, but a similar diet drawn from a different ecological setting. The abundant [C.sub.4] grasses in the Gulf Coastal Plain were not common in the more moist, cooler environments of northeastern North America. Assuming either dietary option 1 or 2 or the combination of both, the [C.sub.4] component of the Ernest Witte diet may be related to the intensification of production in this hunter-gatherer society.

Intensification of production is a consequence of increasing complexity in a hunter-gatherer society along with changes in settlement patterns and decision making (Price and Brown, 1985). In part, this involves the addition of previously avoided lower trophic level species to the dietary pattern that are energetically more costly in terms of procurement and processing. Other consequences of complexity are evident in this region. The development of large cemeteries in the Lower Brazos and Colorado river valleys suggests smaller territories and a restricted subsistence range associated with a reduction in mobility. Violence as a consequence of territorial maintenance and defence is indicated by projectile wounds. Dart wounds have been reported from three sites; Ernest Witte, Group 2 (Hall, 1981), Piekert (Kindall, 1980), and Crestmont (Vernon, 1989). Exotic items included as grave goods with some individuals may indicate differentiation of social roles and status.

If the Ernest Witte data were interpreted as indicating 15 percent of the total diet was comprised of [C.sub.4] grass seed and small mammals that ate [C.sub.4] grass, and these species represent intensification of the subsistence quest, then it should be possible to use diet along with the above consequences to model hunter-gatherer complexity in southeastern Texas. An increased dependence on lower tropic level foods and a broader dietary base should correlate with evidence of increased complexity in other aspects of the archaeological record.

The diet of the dog is 95[+ or -]8 percent [C.sub.3] based. Whatever [C.sub.4] foods were available to, and consumed by human populations were largely kept from, or avoided by, dogs. The isotopic similarity of human and dog diets at the Ernest Witte site suggests a close dietary relationship between the two species. Similar relationships are seen at other sites in both the New World (Katzenberg, 1989) and Mesolithic-Neolithic northern Europe (Noe-Nygaard, 1988).

CONCLUSIONS

Stable carbon isotope analyses of human skeletal remains from the Ernest Witte site in Austin County, Texas, indicate that the bulk of dietary intake of humans at this site were derived from [C.sub.3] pathway based food stuffs. These results support the hypothesis that the subsistence base of these Late Archaic peoples were based on super-abundant terrestrial foods. The [C.sub.4] pathway component of the diet may have been comprised of grass seeds and small mammals. It is hypothesized that this portion represents intensification of production as a consequence of increasing social and technical complexity.
TABLE 1. [[delta].sup.13]C Values for bone collagen (in permil).

Species Sample no. Burial no. Sex Age

Homo sapiens 226 14 M YA (1)
Homo sapiens 227 16 M YA
Homo sapiens 228 34 M YA
Homo sapiens 229 41 M YA
Homo sapiens 230 52 F YA
Homo sapiens 231 70 F YA
Homo sapiens 232 92 M YA
Homo sapiens 233 114 M YA
Homo sapiens 234 136 M YA
Homo sapiens 235 192 F YA
Canis familiaris 251 Fea. 11 - -

Species GG (2) [[delta].sup.13]C

Homo sapiens + -18.4
Homo sapiens - -19.1
Homo sapiens - -19.0
Homo sapiens - -20.5
Homo sapiens + -18.3
Homo sapiens - -18.8
Homo sapiens + -19.9
Homo sapiens - -19.9
Homo sapiens + -18.9
Homo sapiens + -19.4
Canis familiaris - -20.7

(1) Young adult.
(2) Grave goods.


ACKNOWLEDGMENTS

This research was supported in part by The Texas State Higher Education Coordinating Board Advanced Research Program Grant "Continuing studies of ancient Texas indian economies: diet, environment and human adaptation" (awarded to Thomas R. Hester), Project no. 003658-502 (JAH); and The Texas Agricultural Experiment Station, Project H-6945 (TWB). We thank Andrew Midwood, Daniel Watts, and Xing Wang for technical assistance in the laboratory. We also wish to thank Tom Hester, Karl Butzer and Dave Robinson, along with reviewers Grant Hall and Mark Lynott for their commentary and advice. Thanks also to Dan Julian for his computer skills in drafting Figure 1.

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JEFFERY A. HUEBNER AND THOMAS W. BOUTTON

Texas Archeological Research Laboratory, The University of Texas at Austin, Austin, Texas 78712-1100, and Department of Rangeland Ecology and Management, Texas A & M University, College Station, Texas 77843-2126.
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Author:Huebner, Jeffery A.; Boutton, Thomas W.
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:Feb 1, 1992
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