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the Alseseca Arroyo the fossilised leg bone of an elephant-like creature. Firmly embedded in the bone was a flint spearhead.’ Obviously, someone at some time had actively hunted that ani- mal. But who? And when? The questions intrigued Juan, and he was hooked. For the next 30 years he spent much of his spare time searching for more evi- dence of these early hunters. His search was well rewarded. During that time he located well over 100 partial skeletons of butchered mastodon and mammoth as well as many others of the smaller game animals. Missing were the parts rich in meat. Often the bones he found showed signs of human activity. There were intentional cut marks on some of the bones, made during butcher- ing operations. He found splinters of bone, sharpened, smoothed and made into tools; bones cracked to remove the marrow (a food delicacy for primitive hunters even today); a fragment of engraved mastodon pelvis, worked when the bone was fresh; and even a mammoth jaw with an embedded spearpoint. And what of the archaeological establishment in Mexico City during this time? They ignored Juan and his evidence, declaring that all of it—including the engraving and the spearpoint in the mammoth jaw—was the result of Nature, not Man. sites were El Horno, El Mirador, Tecacaxco and Hueyatlaco. Hueyatlaco was the one they concentrated on during the ensu- ing field seasons. It had lots of fossil bones and two distinct arti- fact types: rather simple-looking tools (unifacial tools), made by chipping the edges of natural stone flakes, found in a lower, older sedimentary layer; and more complexly worked pieces (bifacial tools), found in several upper, younger layers. Capping the arti- fact-bearing beds was a thick cover of younger sediment that con- tained several volcanic ash and pumice layers. Both tool types included projectile points (spearheads) and both were associated with butchered bones from very large mammals such as the mastodon and mammoth. This was exciting news! It meant that the tool-makers, whoever they were, were actively hunting and killing these large prey, not simply cutting up a dead carcass they happened upon. Next step was to date the Hueyatlaco site, but a problem quick- ly arose. No carbon (charcoal, wood, shell) had been preserved at any of the four sites including Hueyatlaco. Without carbon there can be no “C dates, and “C is the common radiometric method used to date archaeologic remains in the New World. There was fossil bone in plenty, and bone usually contains carbon, but the bones from these sites had all been permineralised, fossilised, turned to stone. Whatever carbon had been there was now gone. And the sites just had to be dated! Evidence from two other areas in Mexico where ancient stone tools had been found— Caulapan, about five kilometres northeast of Hueyatlaco, and Tlapacoya, south of Mexico City—suggested that Hueyatlaco, the youngest of the four sites found by Armenta and Irwin-Williams, could be as old as 22,000 years. This would make it more than twice as old as any date accepted in the 1960s as evidence of humans in the New World. Textbooks would have to be rewrit- ten. It would make our careers! THE VALSEQUILLO PROJECT Fortunately the research didn't end there. Other scientists besides the archaeological elite in Mexico City learned of Juan's work. They realised its importance and that an in-depth study of the area was imperative—a study that would include input from archaeology, geology, palaeontology and other more esoteric fields. Wheels were put in motion both in Mexico and in the United States; funds were found; and in 1962 the Valsequillo Project was born. Cynthia Irwin-Williams, a young anthropologist from Harvard, was tapped to work with Juan. That first summer exploring together, they located four sites on the north shore of the Valsequillo Reservoir where fi ised bones and stone tools occurred together in situ—that is, within the sediment layers and not just lying loose on the surface. From oldest to youngest, these together, they located four sites on the north shore of the TESTS ON THE TEPHRA LAYERS Valsequillo Reservoir where fossilised bones and stone tools It was the lack of carbon and the need to date Hueyatlaco that occurred together in situ—that is, within the sediment layers and brought me to the project in 1966. I was a young, enthusiastic not just lying loose on the surface. From oldest to youngest, these graduate student at the time—a volcanic ash specialist (tephrochronologist) looking for an interest- ing research project for my doctoral disser- aad tation. At the site itself were several overlying went younger ash and pumice layers (tephra lay- ers). The surrounding badlands contained hundreds of other volcanic deposits. On nearby La Malinche volcano, the project geologist Hal Malde had already dated a series of tephra layers by the '“C method, using charcoal from the carbonised logs they contained. Employing the microscope techniques I had learned at the university, I was certain I could help the other project scientists date their butchered bones and stone tools. I would match up the undated volcanic layers at the site with the dated layers on the vol- cano. Find even one match, and I had a pair of samples that came from the same erup- tion. Same eruption, same date. The site would then be dated indirectly. Simple—or so I thought! So my work began. Years went by. I Map of the area. The sites discussed lie along the north shore of the Valsequillo Reservoir, south of examined tens of samples, hundreds of sam- the City of Puebla. ples! No luck. No correlation. 56 + NEXUS 0 1 2 Km. [ eee Map of the area. The sites discussed lie along the north shore of the Valsequillo Reservoir, south of the City of Puebla. AUGUST - SEPTEMBER 1998