Analysis of Kaqchikel Skeletons: Iximché, Guatemala

Previous Related Work at Iximché

In 1991 Edgar Vinicio García of the Instituto de Antropología e Historia introduced Whittington to the site and its excavation history. In 1992 Dave Reed of Penn State University and Whittington began work on the skeletons at a laboratory in Guatemala City. Whittington returned again in 1993 and then, with funding from the Foundation for the Advancement for Mesoamerican Studies, Inc., for a last time in 1995 to perform analysis of age, sex, trauma, and diseases on the skeletons.

At least 66 whole and partial crania are present in the human skeletal sample stored at Iximché. Except for cervical vertebrae it generally is not possible to match cranial with postcranial material due to mixing and loss of provenience information which occurred in storage between the time of excavation and analysis. Guillemin’s notes and publications indicate that at least 50 crania are from decapitations. Only 17 of the 66 crania could be visually matched with excavation photos of crania which Guillemin identified as decapitations. These are considered to be confirmed Decapitations. Nearly all of them have damage identified as arising from the process of decapitation on the cranial bones or on associated cervical vertebrae. The majority came from a group of 48 decapitated crania deposited together adjacent to Structure 104 in Plaza C, which Guillemin identified as a skull rack.

Fourteen of the 66 crania are Decapitations?, which fall into one of four categories. For 11, damage identified as arising from the process of decapitation appears on the crania or associated cervical vertebrae, but they could not be matched with crania in excavation photos. In one case, documentation found with the bones appears to be reliable and places it within the group of 48 decapitations, even though the cranium could not be matched to an excavation photo and no decapitation damage appears. In one case, the cranium was associated with postcranial bones, but decapitation damage also appears. Finally, in one case, a cranium with decapitation damage was matched to excavation photos which also show its association with a complete postcranial skeleton, which could not be located in storage.

Three of the 66 are Non-decapitations? For these individuals provenience information found with the crania indicated they were part of burials of intact bodies, but the postcranial bones had become separated in storage and could no longer be identified with certainty. Decapitation damage does not appear on these crania.

Four of the 66 are Non-decapitations, intact or nearly intact skeletons which exhibit no signs of decapitation.

The remaining 28 crania lack physical or documentary evidence of their archaeological context. Contextual information is also lacking for cranial bones which could not be assigned to any of the 66 groupings.

Since many crania were fragmentary after their years in storage, a methodology for determining sex was developed with the goal of reducing bias to a minimum. Simple presence or absence of 17 traits, eight characteristic of female crania and nine characteristic of male crania (Table 1), according to Bass (1971), were recorded for each individual. No attempt was made to record degree of expression of the traits. As many traits were evaluated as possible, given each individual’s state of fragmentation. If eight or more traits could be evaluated and at least 75% of them pointed to one sex the individual was evaluated as Male or Female. If eight or more traits could be evaluated and 67% to 74% of them pointed to one sex, the individual was evaluated as Male? or Female?. If between four and seven traits could be evaluated and all of them pointed to one sex, the individual again was evaluated as Male? or Female?. Using these criteria, 10 crania were identified as Female and 11 were Male, seven were Female?, and 10 were Male?. One additional bone which could not be connected to any of the larger cranial groupings was Female? and another was Male?.

Five crania were determined to have come from Subadults (younger than age 15) because of their small, thin bones and the state of their dental development and tooth eruption. Ubelaker’s standards (1989:64) for dentition in Amerindians were used for aging subadults. An additional six bones which could not be matched with any of the larger cranial groupings also came from subadults. Eleven crania and six additional bones which could not be connected to any larger groupings had third molars with roots which had not yet completely formed. The best estimate of the ages of these individuals is approximately 15 to 21, and they can be called Young Adults. The remaining individuals can only be classified as Adults (age 15 or older). The Adult and Young Adult categories overlap. It is likely that some Young Adults are classified as Adults because they lack dentitions, have third molars with incomplete root development hidden within mandibles or maxillas, or had root closure occur at a relatively young age. Despite this, the average age of Young Adults undoubtedly is lower than the average age of Adults. It is clear that the age distribution of this sample does not resemble that of a normal population.

Table 2 is a cross-tabulation showing the number of individual crania classified into different categories of age, sex, and type. The data are much too sparse to allow meaningful statistical analysis of patterns, but a few aspects of the table are worth noting. The characteristics of individuals identified as Decapitations provide some insights into highland warfare and human sacrifice on the eve of the Spanish Conquest. While the majority of victims were males, at least some were females. A large proportion of victims falls into the Young Adult category. It is logical that either captive warriors or non-combatants from settlements within enemy territory chosen for sacrifice would be in the prime of life. Sacatapequez rebels fighting Iximché captured and sacrificed women and children (Borg, n.d.), and a similar practice may explain the presence of female victims at Iximché. However, the females may have been combatants. The Anales de los Kaqchikeles (Recinos, 1988:90) indicates that women from Iximché went into battle as warriors at least once.

All but one of the decapitated individuals have physical evidence on the base of the skull, the vertebrae, or both of the decapitation process. Decapitation must have been a slow, messy process, since the tool of choice was a stone knife or ax with a jagged, almost serrated edge. Decapitation is one of the common forms of sacrifice depicted in Classic period (A.D. 250-900) Maya art (Schele, 1984) and pressure-flaked stone axes and leaf-shaped stone knives frequently appear in painted and sculpted sacrificial scenes throughout Mesoamerica (Boone, 1984). At Iximché, widespread damage typically occurs on the structures of the base of the skull, including the edge of the foramen magnum, the mastoid process, the inferior surface of the occipital, and the posterior angles of the mandible. Vertebrae deposited with the cranium frequently are heavily damaged or even cut completely through. Damage occurs in standardized patterns so that decapitations not positively identified from excavation photos can be tentatively identified. Trauma apparently associated with the process of decapitation occurs on the cranium or vertebrae of 29 of the 66 individuals in the overall sample. It also occurs on 12 mandibles and one temporal which cannot be matched to any of the 66 individuals (Table 3).

David Reed subjected 18 human ribs and a dog mandible from Iximché to stable isotope analysis at the Mass Spectrometry Laboratory at Penn State University. Analysis of stable isotopes of carbon and nitrogen in the non-mineral portion of bone, called collagen, can be used to infer diet (DeNiro and Epstein, 1978; 1981). The turn-over of stable isotopes in bones means that they reflect the diet during the last few years before death. Preliminary results for Iximché have been published previously (Whittington and Reed, 1994; 1998). A summary of these publications follows, along with final results, with minor corrections, as presented by Reed and Whittington (1995) and Whittington et al. (1996).

Measures of isotopic composition of a material are expressed in per mil (‰) as the deviation, or delta (d), of the ratio of heavy to light isotopes in the sample from the ratio in a reference sample. Isotopic ratios can be related to terrestrial plants or marine sources (DeNiro, 1987). Terrestrial plants can be divided into three types, based on type of photosynthesis, each with its own carbon isotopic signature (Coleman and Fry, 1991). C3 plants are leafy and include legumes, while C4 plants are tropical grasses such as maize. Stable isotope analysis of carbon and nitrogen in skeletal tissues may be used to differentiate between the consumption of C3 and C4 plants (with average carbon isotope ratios of -26‰ and -12‰ respectively), and between terrestrial and marine diets (the latter with enriched isotope ratios in both C and N) (Ambrose, 1993). Experimental studies using rats fed isotopically-controlled diets have shown that bone collagen, the non-mineral portion of bone, is produced primarily from protein components of the diet (at least when the overall diet contains sufficient protein). Isotopic signatures, together with paleobotanical, paleopathological, and social interpretations derived from the archaeological record, provide a direct method of determining diet.

In Guatemala, Reed sorted all ribs found together in each storage bag by morphology, preservation, size, side, and location within the rib cage. He preferentially chose fragments of the first rib for analysis, in an attempt to avoid sampling individuals twice. When a skeleton that appeared not to have been sampled had no first rib, he took fragments of another rib. He also took a fragment of the mandible of a dog to compare the diet of a domesticated animal.

After analysis at Penn State, he discarded the results for five of the rib samples, three because they may have been from previously sampled individuals and two because they were extreme outliers. The latter two samples might represent some subgroup, but the individuals share no obvious social, demographic, or pathological characteristics. For the remaining 13 human ribs, the mean value for nitrogen is 7.9‰ and the mean value for carbon is -7.8‰ (Table 4).

Wright and White (1996) summarized isotopic composition of human collagen at 14 Maya sites, including Iximché. The mean nitrogen value for Iximché is low in comparison to most other sites, except Itzán and Copán. The mean nitrogen isotope value indicates that the highlanders buried at Iximché ate an exclusively terrestrial diet, while residents of some other sites included a marine animal component in their diets. The mean carbon isotope value at Iximché is similar to values for people who eat a diet composed of a high proportion of maize. The specimens from Iximché have a more positive mean carbon isotope ratio than any other site presented by Wright and White. This probably reflects not only dietary differences between the sites, but also Iximché’s 2200 m altitude, higher than any other Maya site yet sampled. Researchers have observed that the carbon isotope composition of plants shifts toward less negative values with increasing altitude (Körner et al., 1988; Marino and McElroy, 1991; Polley et al., 1993).

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