Earliest Humans in the Americas New Evidence From Mexico2

Journal of Human Evolution 44 (2003) 379–387

News and Views

Earliest humans in i n the Americas: new evidence from Me´ xico Silvia Gonzalez 1*, Jo Jose se´ Co Conc ncep epci cio oń Ji Jime meńe nezz-Lo Lo´ pe pezz 2, Robert Hedges 3, David Huddart 1, James C. Ohman 1, Alan Turner 1, Jose´ Antonio Pompa y Padilla 2 1

2

School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK Direccioń de Antropologıá á Fisica, Instituto Nacional de Antropologıá á e Historia, Reforma y Gandhi s/n, D.F. C.P. 11560, Mexico 3 Research Laboratory for Archaeology and the History of Art, 6 Keble Road, Oxford OX1 3QJ, UK

Keywords: Pen˜ on III; Tlapacoya I; San Vicente Chicoloapan; Texcal; Tepexpan; Paleoamerican; AMS radiocarbon dating; New World; stable isotopes

Mexico plays an important role in the debate over early human presence in the Americas because of itss geo it geogra graph phica icall po posit sitio ion. n. Hu Human manss mu must st ha have ve passed through the Valley of Mexico, either from the north via Beringia (the Clovis people of the southwestern USA dated ca 11,500 BP) or possibly from South America (evidence from Monte Verde, Chile with a minimum occupation date of 12,500 BP (Dillehay, 1989)). Thee Ba Th Basi sin n of Me Mexi xico co is a la larg rge, e, nat atur ural ally ly closed high plain at an elevation of about 2250 m (Bradbury, 1989). During the Late Pleistocene the basin contained an extensive, shallow lake (Fig. 1) that provided attractive attractive resou resources rces for early human occupants occupa nts (Coe, 1994). Previous excavations in the Valley of Mexico produced human remain inss estim ima ated to be * Corresponding author. author. Tel.: +44-(0)151-231-2213; fax: +44-(0)151-207-3224 E-mail addresses: [email protected] (S. Gonzalez), [email protected] (J.C. Jimeńez-Lo ńez-Lo´ pez), [email protected] (R. Hedges), [email protected] (D. Huddart), [email protected] (J.C. Ohman), [email protected] (A. Turner), [email protected] (A. Pompa y Padilla).

11,000 years BP using stratigraphic criteria at the Tepexpan site (De Terra et al., 1949) and archaeological materials dated as old as 24,000 BP (charcoall in hear coa hearths ths)) at the Tlap Tlapacoy acoya a sit sitee (Lo (Loren renzo zo and Mirambell, Mirambell, 1986). Claims for suc such h an earl early y occu oc cupa pati tion on ha have ve me mett wi with th sk skep epti ticis cism, m, la large rgely ly becaus bec ausee of unc uncert ertaint ainties ies abo about ut the ass associ ociati ations ons betwee bet ween n the arch archaeol aeology ogy,, str strati atigrap graphy, hy, hum human an remain rem ainss and the dat dated ed mat materia eriall (Ha (Hayne ynes, s, 1969 1969). ). Lithics associated with mammoths were found at the Santa Isabel Iztapan I and II sites (Aveleyra Arroyo de Anda, 1956; Aveleyra Arroyo de Anda and Maldonado-Koerdell, 1953), and indicate ages of at le leas astt 11 11,0 ,000 00 ye year arss BP BP,, ba base sed d on ar arti tifa fact ct typologies. One previous attempt to date directly the Tepexpan human skeleton using 14C gave an age around 2000 BP, but this date was rejected due to contamination at the molecular level (Sta ff ord ord et al., 1991). We repor reportt new direct radioc radiocarbon arbon determinadeterminations on five Pre-Ceramic Mexican specimens (four successful). These new dates, which are among the earl ea rlies iestt in th thee Am Amer eric icas as,, in indi dicat catee th that at hu huma mans ns were present in Central Mexico at the end of the Pleistocene.

0047-2484/03/$ 0047-2484/03/ $ - see front matte matterr  2003 Published Published by Elsevier Science Ltd. doi:10.1016/S0047-2484(03)00004-6

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S. Gonzalez et al. / Journal of Human Evolution 44 (2003) 379–387

Fig. 1. Localities with Paleoamerican remains around the Basin of Mexico. Numbers are as listed in Table 1. Texcal Cave in Valsequillo, Puebla State (No. 3 in Table 1) is the only site not located in the Basin of Mexico.

Radiocarbon and Stable Isotope Methods

A total of eleven individuals from the PreCeramic Human Collection in the Museum of Anthropology in Mexico City were sampled to attempt direct AMS (Accelerator Mass Spectrometer) radiocarbon dates on human bone. In each case, samples of less than 2 g of dense bone were taken. Radiocarbon dates were obtained for four human specimens: Penõn III, Tlapacoya I, Texcal Cave and San Vicente Chicoloapan (see Table 1 and Fig. 2). All the dates presented in this paper are in radiocarbon years. A fifth date was considered to be unreliable (Tepexpan Man) because the chemical analysis (the C:N ratio) of material pre-treated for dating (i.e. purified collagen) indicated significant contamination, see Table 1 and discussion below. We were unable to obtain radiocarbon dates in six other human specimens due to the lack of collagen preservation, these specimens

were: Chimalhuacan, Metro Balderas, Santa Maria Astahuacan, Tecolote Cave, Pen ˜ on del Marquez and Penõn IV. On the other hand, the four dates reported on here (Pen˜ on III, Tlapacoya I, Texcal Cave and San Vicente Chicoloapan), were on bones pre-selected from a wider sample to contain a reasonable amount of surviving extractable collagen, levels of which (after purification) are given in Table 1. Typical modern levels are 200 mg/g, and the great majority of Pleistocene/Early Holocene bones from Mexico, both human and animal, that we have examined have extractable collagen at levels of 1 mg/g or less. The specimens reported on here are therefore unusually well preserved examples. We find in general that when collagen levels fall below 2–5 mg/g there is a significant probability that contaminating material of diff erent 14C age can persist through the extraction and purification procedures.

Table 1 Mexican human specimens with direct AMS radiocarbon dates on bone (uncalibrated), and bone chemistry. 13

Specimen

Lab. no.

Specimen no.

Element dated

Age BP



C

1. Pen˜ on III. 2. Tlapacoya I 3. Texcal Cave 4. San Vicente Chicoloapan 5. Tepexpan

OxA-10112 OxA-10225 OxA-10113 OxA-10111 P8919

07/1959/DAF/INAH 16/1968/DAF/INAH 15/1964/DAF/INAH 07/1955/DAF/INAH 03/1947/DAF/INAH

Humerus Cranium Mandible Cranium Rib

10,75575 10,20065 748055 441050 2290*

11.6 15.4 14.4 14.6 19.8

15



N

13.6 10.6 11.0 9.7 –

C:N

Collagen mg/g

Cranial index

3.5 3.5 3.5 2.6 15

50.3 10.9 12.3 16.5 0.4

70.05 67.67 80.66 72.67 79.44

* The determination for Tepexpan is shown without confidence limits. The results of the chemical analyses suggest that considerable molecular contamination with preservatives has occurred, so this date cannot be accepted as a true indication of age (see discussion in text).

S . G o nz a l e z e t a l . / J o ur n a l o f H u m a n E v o l u t i o n 4 4 ( 2 0 0 3 ) 3 7 9 – 3 8 7

3 8 1

382


382


Fig. 2. Radiocarbon dated Mexican Paleoamericans. a, Skull of Pen˜ on III Woman (07/1959/DAF/INAH) in frontal view. b, Calvaria of Tlapacoya I Man (16/1968/DAF/INAH) in frontal view. c, Skull of Texcal Man (15/1964/DAF/INAH) in frontal view. d, Calvaria of San Vicente Chicoloapan Man (07/1955/DAF/INAH) in frontal view. e, Skull of Tepexpan Man (03/1947/DAF/INAH) in frontal view.

Our procedure for collagen extraction and purification was standard (Bronk-Ramsey et al., 2000). It included a non-polar solvent extraction (50% W/V methanol/chloroform) to remove additives during museum conservation, followed by decalcification in hydrochloric acid, filtration, gelatinisation of the insoluble collagen in the residue, and subsequent ultrafiltration to retain the >30 kD soluble fraction. However, this does not guarantee that the product contains only pristine collagen; indeed collagen in bone degrades over time and loses chemical definition. More specific methods require more sampled material than is available. We used two methods to check on the

chemical integrity of the product in the four dates reported here: (a) the measurement of the ratio of carbon to nitrogen (C:N) and (b) infrared spectrometry. The quantity of contamination that is significant depends on its age, 3% of modern carbon would be su fficient to make a 10,000 BP date a thousand years too young, while 10% of a geologically ancient contaminant would make it a thousand years too old. A 10% addition of nonproteinaceous material should be detectable by either anomalous C:N values (normal values are between 2.9 to 3.6, see Table 1), or by the presence of additional peaks in the infrared spectrum. We


are confident that non-protein contamination is not generally present at such levels in the samples reported here. The exception appears to be Tepexpan Man, where the visual impression of extensive treatment with preservatives is confirmed by the C:N value of 15 (Table 1), and we therefore believe that the determination of 2290 BP cannot be accepted as a true indication of age. Most potential environmental contaminants are likely to have an intermediate age, and so have a lesser eff ect on the radiocarbon age. This is evident in the case of the Tlapacoya specimen (Table 1). Although this finally gave a date of 10,20065 (OxA-10225) it had previously been investigated using a less elaborate, standard laboratory procedure (no solvent extraction and no ultrafiltration). The date obtained (9730 65 OxA-7557) is significantly, but not grossly, younger than OxA10225. It therefore appears that even when less stringent methods are used the basic antiquity of the date is still obtained, implying that there may be some younger contamination in the sample but that it is relatively easily removed by the additional processing. This does not necessarily apply to all the bone measured, but does help to confirm the early date. Here, contamination post-excavation by unrecorded petroleum-based preservatives may be suspected; fortunately such additives are rather easily detected by infra-red spectrometry and their absence increases our confidence that the dates reported here are not a ff ected by significant levels of contamination. The analysis of the stable isotope composition of human and animal bones provides direct information on the lifetime diets of those organisms. From the collagen fraction extracted during the radiocarbon dating of the Mexican Paleoamericans, we have obtained data on their stable isotope composition ( 13C and 15N, see Table 1). To compare the data obtained from the humans, values obtained for some Mexican megafauna including: mammoths (Mammuthus columbi ), camel (Camelops hesternus) and groundsloth (Nothrotheriops shastensis) are included in Fig. 3, together with some data from Alaskan (M. primi genius) and Siberian Mammoths (M. primigenius). All the mammoth collagen that we have measured

383

from this period and earlier shows similar isotopically heavy values.

Results of the human specimens dated directly using bone

El Penõn III El Penõn de los Banõs is a hill surrounded by hot springs in the middle of former Texcoco Lake (Fig. 1). The area produced human remains as early as 1884 (Ba´rcena, 1886; Ba´rcena and Del Castillo, 1884), with much controversy about their age. The Penõn III specimen is a well-preserved human partial skeleton recovered in 1959 (Mooser and Gonzalez Rul, 1961; Romano, 1974). It was found in a sediment “with volcanic tu ff characteristics, humitic, subaquatic and sealed by a layer of travertine of 2 m in thickness” (Mooser and Gonzalez Rul, 1961). The site has no evidence of pottery. Penõn III includes the skull (Fig. 2a), and much of the postcrania, though lacking femora and tibiae. The cranium is dolicocephalic (longheaded), with a cranial index of 70.1 (Table 1). Both cranial and postcranial evidence indicate a female with an age-at-death of about 25 years, although the teeth are very worn, a characteristic common in the Pre-Ceramic humans from Mexico. The AMS radiocarbon date of 10,75575 BP (OxA-10112) for this specimen is currently the earliest from Mexico (see Table 1). Tlapacoya I Tlapacoya is a prehistoric site adjacent to a volcano in southeastern former Lake Chalco (Fig. 1), discovered in the 1960s during motorway construction (Lorenzo and Mirambell, 1986). Tlapacoya I Alpha trench produced a number of animal bones associated with pebbles and what were considered to be artefacts and hearths on a lakeshore. Conventional radiocarbon dates of 24,0004000 (A-794b) and 21,700500 (I-4449) were obtained (Haynes, 1967), from humic soil extracts and charcoal thought to come from hearths (Lorenzo and Mirambell, 1986).

384


Fig. 3. Preliminary stable isotope data for Mexican paleoamericans and megafauna bone collagen. Square symbols are used for Mexican Paleoamericans (numbers 1 to 4), triangles for megafauna (mainly mammoths). The species of the Mexican mammoths is M. columbi . Siberian Mammoths are M. primigenius (numbers 12 and 13); Alaskan Mammoths are M. primigenius (numbers 14 to 16). The graph shows the values of collagen  13C, which are believed to register mainly the carbon in the protein component of the humans paleodiet. The values indicate a significant proportion (30–70%) of either C4 or CAM plant photosynthetic sources of protein carbon for the humans. It is likely that the large  15N values would be passed up to the humans via grazing herbivores, like for example the Columbian mammoths. However the values are very diff erent for the Siberian and Alaskan Mammoths which belong to a di ff erent species and diff erent habitats. Mexican specimens description by number: Paleoamericans: (1) Pen˜ on Woman III, 10,755 years BP. (2) Tlapacoya Man, 10,200 years BP. (3) Texcal Cave Man, 7440 years BP. (4) San Vicente Chicoloapan Man, 4410 years BP. Megafauna: (5) La Villa Mammoth, 11,300 years BP. (6) Tocuila Mammoth, 11,100 years BP. (7) Los Reyes-La Paz Mammoth, 18,280 years BP. (8) Santa Lucıá Camel, 11,395 years BP. (9) Carretera Mammoth, 16,380 years BP. (10) Hacienda de Hornos Mammoth, 10,550 years BP. (11) San Josecito Cave Ground sloth, 19,740 years BP.

Tlapacoya I Beta trench produced a date of 22,0002600 (A-790 A) for a layer containing a quartz scraper (Lorenzo and Mirambell, 1986). In trench Tlapacoya XVIII, 25 m southwest of Tlapacoya I Beta, a human cranium was reported in a horizon with a 14C date of 9920250 (I-6897) (Garcıá-Ba´rcena, 1986), but no stratigraphic details were given. The cranium is heavily covered in preservative material and no attempt was made to date this specimen for this study.

In 1968 excavators learned of a second human cranium that was previously discovered by road crews about 50 m north of Tlapacoya I Beta, and re-buried under some stones (Mirambell, 1986). No stratigraphic detail was preserved (Lorenzo and Mirambell, 1986). The reburied and recovered Tlapacoya specimen lacks the facial skeleton and much of the basicranium (Fig. 2b). It is dolicocephalic with a cranial index of 67.7 (Table 1). The specimen represents a male with an age-at-death of


30–35 years. This cranium (16-1968/DAF/INAH) yielded a preliminary age of 973065 BP (OxA7557). Given the importance of the result, a second analysis using more stringent laboratory procedures to “clean” any possible contamination (see radiocarbon methods section) yielded an earlier date of 10,20065 BP (OxA-10225) (Table 1). Texcal Cave Texcal Cave (Valsequillo, Puebla) was discovered in 1964. The specimen, dated here to 748055 BP (OxA-10113) (see Table 1), was found in layer IV. It consists of an adult male partial skeleton with an age-at-death of 31–35 years (Romano, 1974). The rounded (brachicephalic) cranium has a cranial index of 80.7. The cranium has been reconstructed and is missing the basal portion and both zygomatic arches, while the mandible is fairly complete, although most teeth were lost post-mortem (Fig. 2c). San Vicente Chicoloapan The San Vicente Chicoloapan site (Fig. 1) yielded a fragmentary human calvaria (Fig. 2d) in 1955 (Romano, 1974). The specimen was associated with hearths and lithics but no pottery, despite the late date of 441050 BP (OxA-10111) (Table 1). The calvaria is that of an adult male with an age-at-death of 20–25 years, and a cranial index of 72.7, at the higher end of the dolicocephalic range. Tepexpan Man The Tepexpan site is close to the former shore of Texcoco Lake (Fig. 1). The partial skeleton was recovered in 1947 (De Terra et al., 1949). The skeleton was said to be below a caliche layer, in sediments correlated with the Becerra Formation dated around 11,000 BP (De Terra et al., 1949). A much later date of 1980 330 BP (AA-2667) was obtained by Staff ord (Staff o rd et al., 1991), but rejected due to low collagen levels (Table 1). Our attempt to date the specimen directly produced a similar result of 2290 BP, but the date was formally failed by the Oxford Radiocarbon Laboratory owing to extensive contamination

385

(Table 1). The real age of this controversial specimen is still unknown. Tepexpan is an adult male with an age-at-death of 25–30 years (Fig. 2e). The cranium is meso- to brachicephalic, with a cranial index of 79.4 (see Table 1). Results of stable isotope composition of the human and megafaunal bone

The stable isotope composition of the human collagen (see Table 1 and Fig. 3) is worth commenting on despite the small number of samples. The collagen 13C values, which are believed to register mainly that of the carbon in the protein component of the diet, all show a significant proportion (30–70%) of either C4 or CAM plant photosynthetic sources of protein carbon. Geographical considerations rule out marine resources. While some C4 plants such as maize or millet have been cultivated to yield useful protein resources for humans it is unlikely that wild grasses would have been a dominant protein source, especially considering that agriculture was “discovered” in Mexico much later, at around 6000 years BP (McNeish, 1970). It is more likely that such isotopically heavy carbon would be passed up the food chain via grazing herbivores, possibly including the Columbian mammoths. The mammoth 15N values vary from 9% to 13%—a range rather similar to that for the humans. Mammoths often, but not necessarily, have elevated 15N values when compared with other herbivores (Bocherens and Billiou, 1997), so that the human values are not inconsistent with the predation on other herbivores like the Columbian mammoths. However the values are very diff e rent for the Siberian and Alaskan mammoths which belong to a diff erent species and diff e rent habitats. So far the evidence is tantalizing but much more work is required to clarify the general trend for the paleodiet of the Mexican Paleoamericans. Discussion

In the American Continent as a whole there are few directly dated Paleoamericans. Examples of

386


North American specimens include the Arlington Springs femora from Santa Rosa Island (California) at 10,96080 BP (Johnson et al., 2000); Buhl (Idaho) at 10,67595 BP (Green et al., 1998); the Anzick cranial fragments (Montana) at 10,700 (Staff o rd et al., 1987) and later re-dated to 11,500 (Staff ord, 1999). Spirit Cave (Nevada) at 9415 BP; Wizards Beach (Nevada) at 9225 BP (Dansie, 1997; Green et al., 1998; Jantz and Owsley, 2001) and the controversial Kennewick specimen (Washington) at 841060 BP (Chatters, 2000). In South America a human with a potential age of 11,500 BP has been reported, but the oldest directly dated humans are not older than 9720 BP (Neves and Pucciarelli, 1991). Thus, the dates for the El Penõn III and Tlapacoya I specimens represent some of the earliest directly dated human remains in the New World. They confirm human presence in Central Mexico by the Late Pleistocene, although they do not confirm the earliest dates (ca 24,000 BP) previously published for the Tlapacoya site (Lorenzo and Mirambell, 1986). The Mexican specimens are important in the discussion of the peopling of the New World because they increase the sample of directly dated individuals, and also fill a geographical gap regarding human occupation of the Americas at the end of the Pleistocene. The new direct dates for Penõn III and Tlapacoya I imply the presence in Central Mexico of an early human population of long and narrow-headed people (dolicocephalic) of nonmongoloid affinity by 11,000 BP, adding to the question as to where, and how, this particular population arrived in the Basin of Mexico. The San Vicente cranium suggests that the dolicocephalic population existed as late as 441050 years BP. In contrast, Texcal (7480 55 years BP) is short and broad (brachicephalic). These findings, and the small sample of other directly dated Paleoamericans currently available in the New World seems to indicate great levels of cranial diversity for these early populations. A study reported by Jantz and Owsley (2001) found no morphometric affinity between Early Holocene American crania and Modern Native Americans, instead they found more similarities with European, Polynesians and East Asian

populations. On the other hand, the controversial Early Holocene, Kennewick Man has been interpreted as Polynesian or Ainu, with no mongoloid affinity (Chatters et al., 1999). Studies in South America (Neves and Pucciarelli, 1991; Neves, 2000) found that the first inhabitants have a strong affinity with modern Africans and Australians, with no similarities with the Modern Asian Mongoloids or American Indians. So, at present the evidence indicates great human diversity for the first Americans, with the possibility of several points of origin. However there are, so far, no humans directly dated in the Americas older than 11,500 years BP.

Acknowledgements

Dating of the specimens was funded by: (a) the National Museum of Anthropology, Mexico City with the support of Enrique Serrano-Carreto; (b) the Natural Environment Research Council (NERC) in the United Kingdom. Sampling was helped by Paul Pettitt. Photographs courtesy of the Direccioń de Antropologıá Fı´sica, INAH, Mexico City. Research visits to Me´xico by S. Gonzalez, D. Huddart, J.C. Ohman, and A. Turner were funded by Liverpool John Moores University.

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Earliest Humans in the Americas New Evidence From Mexico2

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