Overview of Central Mexican Prehistory: Morphostratigraphy, Chronostratigraphy, Biostratigraphy

Overview of Central Mexican Prehistory: Morphostratigraphy, Chronostratigraphy,BiostratigraphyAuthor(s): Mario PichardoSource: Anthropologischer Anzeiger, Jahrg. 61, H. 2 (Juni 2003), pp. 141-174Published by: E. Schweizerbart'sche VerlagsbuchhandlungStable URL: http://www.jstor.org/stable/29542453 .

Accessed: 28/09/2013 21:16

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

E. Schweizerbart'sche Verlagsbuchhandlung is collaborating with JSTOR to digitize, preserve and extendaccess to Anthropologischer Anzeiger.

http://www.jstor.org

This content downloaded from 134.53.24.2 on Sat, 28 Sep 2013 21:16:00 PMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=schweizerbart

http://www.jstor.org/stable/29542453?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


Anthrop. Anz. Jg. 61 2 141-174 Stuttgart, Juni 2003

Overview of Central Mexican Prehistory: Morphostratigraphy, Chronostratigraphy, Biostratigraphy

Mario Pichardo

Minneapolis, MN, USA

With 13 figures

Summary: New research indicates an ice-free corridor may have been open for 20,000 years in North America and people could have moved southward even at Last Glacial Maximum. Morphostratigraphie, chronostratigraphic, biostratigraphic and archeological evidence from Central Mexico at Valsequillo, Texcoco/Tequixquiac and Chapala supports this view.

Key words: Central Mexico prehistory, Valsequillo, Texcoco/Tequixquiac, Chapala.

Zusammenfassung: Neue Forschungen lassen für Nordamerika einen 20.000 Jahre dauern- den eisfreien Korridor annehmen, so daß Bevölkerungen südwärts wandern konnten, selbst während des letzten Eiszeitmaximums. Morphostratigraphisches, chronostratigraphisches, biostratigraphisches und archäologisches Beweismaterial von Valsequillo, Texcoco/Tequix- quiac und Chapala in Zentral-Mexiko rechtfertigen diese Annahme.

Schlüsselwörter: Vorgeschichte Zentralmexikos, Valsequillo, Texcoco/Tequixquiac, Cha- pala.

Introduction

The Amerind FAD (= first appearance date) is currently under considerable con- troversy. It has been approached by the study of genetics without arriving at any consensus regarding the antiquity of the first Americans (e.g. Meitzer 1995, p. 31).

Amerind paleontology Paleoindian finds also offer no insights about the FAD since all the reputedly early specimens represent merely a plesiomorphic Homo sapiens americanus Linnaeus. That is, long and lowheaded populations with elongate distal limbs, which are characterized by Neumann's Otamid morph (Neumann 1952). The 14C range appears at present to be ca. 12,800 yr B.P. for El Peñón III, under the UTP (Upper Toluca Pumice) in the Valley of Mexico (Pichardo 2000b); 12,000 - 10,000 yr B.P. for the Midland skull (Holliday & Meitzer 1996), and a maximum of 4,900 yr B.P. for the Del Mar skull (Taylor 2000). This morph continues into the eastern Archaic and Middle Woodland periods from the Texas Coast, Louisiana and the Midwest to New York and Maine (Neumann 1952).

0003-5548/03/0061-0141 $ 8.50 © 2003 E. Schweizerbart' sehe Verlagsbuchhandlung, D-70176 Stuttgart



142 Mario Pichardo

Osteologie adaptations to climate (Pichardo 1998) by this morph and later morphologically derived populations (e.g., Pericue of Baja California) also do not offer clues concerning origins since the long-headed and long-limbed morphology is found in late Pleistocene populations from Europe to Siberia. Computer taxonomy by character distance statistics using many characters (e.g. Steele & Powell 1992) has not been able to advance beyond the morphological analyses of the earlier studies (Neumann 1952, Newman 1953). They also conclude that earlier Archaic and Paleoindian populations appear less markedly Mongoloid in cranium and face.

The only population suggesting a more primitive morphology is the small thick- boned sample from Lagoa Santa, Brazil (a calotte and a frontal-orbital fragment, both now lost; Bryan 1978). I am obliged to categorically reject my suggestion (Pichardo 1998) that some limb bones of a giant ateline from Lagoa Santa might be referred to the same hypodigm. Bryan's specimen is unquestionably human.

However, there are further issues which need clarification. The semi-lunar shape of the thick supraorbital arches does not resemble that of the Mapa skull from China, as was suggested. Bryan (1978, p. 321) notes that the normal Lagoa Santa population is characterized by a broad interorbital distance and low naso-frontal suture also (cf. Soto-Heim 1994, Fig. 6). Moderately robust browbridges are present in the Otavalo skull from Ecuador (Lynch 1990), and thick-boned cranial remains are now reported from Chapala, Mexico (Solorzano 1995, Irish et al. 2000). Whether there exists any genetic link between any of these far-ranging thick-boned specimens which would indicate a hypothetically early population is speculative at this point.

A possible explanation for occurrence of this unexpectedly archaic morphology in Brazil may be a unidirectional genetic introgression through hybridization, by which the hybrids strongly resemble one genetic source more than another. It has been shown to occur in White-tailed/Mule deer crosses (Carr & Hughes 1993) and has been proposed as an explanation for the late Pleistocene Bison antiquus/occi- dentalis morphs of the Central Plains (Wilson 1996). Paradoxically, this explanation was clearly anticipated by Birdsell (1951) in his discussion of 'Caucasian', or Amurian, traits in the Cahuila, Cupeño, Luiseño and Serrano of southern California, the Pomo, Miwok of northern California and the southern Paiute of Nevada.

Artefact typology Recent computer simulation modeling of possible movement corridors into America (Anderson & Gillam 2000) are still made with reference to fluted point distributions. Many assumptions about subsistence strategies, population size and reproductive rates render these exercises as also speculative. The most recently advocated Clovis ancestor, the Alaskan Nenana Complex, has been questioned because it lacks the characteristic Clovis points, and a microblade component has been found in some sites (Meitzer 1995).

The impass is best explored by the suggestion that contrasts between Alaskan (or even Siberian) and Clovis industries reflect rapid adaptive shifts in technology and tool kits as migrants expanded southward into new environments. This assumption however is dependent on, and questioned by, empirical biostratigraphical evidence



Overview of Central Mexican Prehistory 143

discussed below. But even on typological grounds the origins of the Clovis point, and the inferred mammoth-hunting specialization, can be argued to have evolved from an earlier stemmed point tradition of which the Sandia (single-shoulder) point is a variant. Basal fluting of Sandia points occurs at the Lucy site, New Mexico (Wormington 1957).

Linguistics Linguistic evidence on the contrary has consistently indicated that divergence of Amerind languages must date to at least the time of the mid- Wisconsin Interstadial (Gruhn 1988, Nichols 1990), which ranges from 32,000 - 21,000 yr B.P. (Mickelson et al. 1983). In accord with Birdsell's morphologic observations (Birdsell 1951), the great multiplication of major subdivisions of given language families along the Pacific Coast (Gruhn 1992) indicates that this may have been a primary center of dispersal into the interior. Gruhn (1992) makes the point that although the number of individual languages may multiply for various causes, the great subdivisions of families take considerably longer to develop. Language family isolates in other areas like the Gulf Coast suggest a shatter pattern of relict groups which were pushed marginally by expansion of later population movements.

A more recent approach proposes that distribution of many language families can be understood in terms of barriers which no longer exist. The earliest date of the barrier's existence gives a minimum date for the linguistic event (Rogers et al. 1990). Barrier dating for the LGM (last glacial maximum) shows that boundaries of biogeographic zones form linguistically significant barriers. A new set of adaptations is required to move from one zone to another - the adaptive-shift postulated from the evidence of tool typologies.

The center of a language family's major subdivisions is assumed to be the center of dispersal. Whereas the area once covered by Wisconsin ice is devoid of language isolates, there are at least thirteen language isolates, most of them south of the area covered by ice (Fig. 1, lower). At the end of the Ice Age the Algonquian Group moved into Canada and the Nadene dispersed southward as far as the Southwest. The Wiyot and Yurok languages of northern California, however, are distant relatives of the Algonquian and are collected into the Algic Family. Maximum diversity within Algic is found in the California groups, with the inference that there was an eastward dispersal of Algic. Carlson (1983) proposes that Algic (Macro- Algon- quian) speakers were the linguistic group associated with the fluted point tradition of the Plains and which dispersed eastward into the park woodlands in late Wisconsin time. Likewise, the stemmed-point tradition of the Great Basin he correlates with the Macro-Penutian speakers. Gruhn (1988) indicates the Uto-Aztecan (or Aztec-Tano- an of Rogers et al. [1990]) home was along the lower Colorado River. It implies later widespread dispersal northward flanking the Rockies, the Southwest and into Mex- ico - all necessarily during the LGM 30,000 - 10,000 yr B.P.

Although it can be assumed that some of the Gulf Coast language isolates may have been involved in migrations far to the south, only the major groups outlined above are here discussed with reference to the Amerind FAD.



144 Mario Pichardo

100*

ÔICROSTONYX- OVIBOS^ C

«0* 100» »0* 100*

12#* too* »0*

Fig. 1. Correlation between Pleistocene Faunal Provinces (upper) and major divisions of Amerind language families (lower), which can be 'Barrier Dated'. For example: Algonquian and Nadene languages could not have spread north and south of ice-covered areas until after ca. 12,000 yr B.P. Algonquian distribution may correlate with an earlier eastward dispersal into the Symbos-Cervalces faunal province of the eastern woodlands at the time of the eastern dispersal of fluted points. See text for discussion. Adapted from Rogers et al. (1990).




Biostratigraphy The Barrier Dating paradigm (with the exception of coastal migrations) unexpectedly restricts biogeographic zonation to that of the Camelops faunal province of paleontologists (Fig. 1, upper); Rogers et al. (1990), Graham et al. (1996). The Camelops fauna was characterized by large grazing and browsing mammals including mammoth, horses, bison, scrub-ox, mastodon, deer, antilocaprids, large ground sloths, and the omnivore short-faced Arctodus. Individual species ranges shifted independently of one another producing faunal associations not found in Holocene climatic regimes (Graham et al. 1996). The diverse flora included montane conifers and oak park lands, shrub and grassland.

During the LGM the Rockies were an even greater barrier to movement because of the lowered snowline. Only the northern Paiute represented the Aztec-Tanoan languages. Conifer forest covered most of the northwestern edge of the province, home of the Penutian languages. Penutian speakers may have at least shared, with any other extinct or departed language isolates, the origin and spread of the stemmed point tradition in the Great Basin.

A great north-south series of pluvial lakes formed from Oregon through the Great Basin into southern California and into what is now the central Chihuahuan desert. The bifacial stemmed-point tradition, which included leaf-shaped points as well as flake tools, occupied a niche of generalized hunters and foragers in these lake habitats. This culture had diffused to the Southwest by the time of the Sandia-point manifestation and as the climate progressively deteriorated towards greater aridity the tradition had 'niche-shifted' into what had become a true Desert Culture (Irwin- Williams & Haynes 1970). Perhaps this was the period of major dispersal of the Aztec-Tanoan languages.

Fig. 2 illustrates the compromise which must necessarily be made between empirical data and the constricts of hypotheses. Prehistorians have known for over fifty years that populations from Central Europe, the Russian Plain and as far east as Lake Baikal in Siberia began to occupy an Open Plains Niche during the time of Aurignac oscillations (a mid- Wisconsin Interstadial isochron). The Kostenki sites along the middle Don River on the Russian Plain (Kostenki 5, level 1) show great typological similarity to the Clo vis tool-kit, including concave-base points with slight fluting. This parallel typological trait demonstrates the basic flaw in long range temporal/ spatial correlations (Müller-Beck, 1966, Haynes 1976).

The bifacially retouched 'Streletskaya' tools at Kostenki were made by groups that foraged for greater diversity in harvested resources which provided a more opportunistic feeding pattern than that of the roughly contemporaneous 'Spitsyn' Culture. The latter had a more classic Aurignacoid tool-kit with prismatic cores, blade tools and some worked bone. That the latter group ranged widely is shown by the exotic flint they quarried as far as 300 km southwest of Kostenki. Their resource strategy required limited exploitation of a few species, seasonal migrations and more organized planning (Soffer 1989). Even if Aurignacoid microblades were diffused into Alaskan Nenana sites above mentioned the fact remains that this basically bifacial tool-kit was twenty thousand years younger than similar tools on the Rus- sian Plain or Siberia (Vasil'ev 1993, Goebel et al. 1993).

The study of Amerind morphology indicated that too fine a resolution into details



146 Mario Picharão

may mask the simpler but more realistic empirical facts. This is why I advocate a paleontological approach to Amerind taxonomy (Pichardo 1998). It is not possible to determine whether a statistical study of 'all' traits is not sorting morphs on the basis of covert added weight given to similar dimensions taken on traits from populations of possibly diverse genetic origins. In a like manner, I follow the views of Müller-Beck (1966) and Haynes (1969, 1976) to illustrate that it was indeed possible for a bifacial tool-kit in a more generalized hunting-foraging culture to have entered America as early as the mid- Wisconsin Interstadial (Fig. 2, upper). At a later date, perhaps when the stemmed-point/leaf-point bifacial tradition was well established it dispersed as far as Central Mexico. The Aurignacoid blade culture came into contact with this earlier culture during the Two Creeks Interstadial (Fig. 2, lower). The Big Game hunting specialists of North America may have gotten the 'mind-seť for their Spitsyn-like nomadic specializations through cultural diffusion, but the fluting of projectile points may have been a fortuitous stylistic or functional (hafting) trait which paralleled that of Kostenki 20,000 years earlier.

Empirical data establishing species taxonomy (when possible) and radiometric dates are kept to a minimum in Fig. 2, and used merely as an expository device to encourage students to think along the lines of solid, dated, established evidence. First to be dissected is the cliché regarding a 'mid- Wisconsin' and a Two Creeks' interstadial marker horizons. There are presently at least eight interstadials recognized between Plum Point/Farmdale time and Two Creeks (Mickelson et al. 1983).

In the west, a similar pattern is emerging for the Tee-free Corridor' (Carrara 1995, Wilson 1996, Heine 1998). Although areas south of Grand Prairie were not ice-free until ca. 12,000 yr B.P. in the Alberta Corridor, slope deposits in the Columbia Mountains west of the Rockies, British Columbia, experienced perma- frost climate conditions indicating these regions were unglaciated for at least 20,000 years (Heine 1998). This accords with Mickelson et al. (1983) regarding climatic oscillations during the LGM, and 'people from Beringea could have crossed the areas between the Laurentide and Cordilleran ice sheets even during the LGM' (Heine 1998, p. 19).

There is moreover paleontological and 14C evidence which supports that of geology, which has been unrecognized because of the unyielding 'mid- Wisconsin/ Two Creeks' markers premise. In Fig. 2, upper, two Yukon sites are selected to demonstrate the complications: Gold Run Creek in the south and Old Crow Basin in the north. What at fist appears to be a confusing array of dates and species becomes clear once the foregoing discussion about climatic oscillations that oc-

- - ^ Fig. 2. The seeming complexity of wide-ranging 14C dates and cold vs. warm faunal sequen- ces is addressed by recent work, which demonstrates that there were at least eight interstadial oscillations between the Plum Point and Two Creeks interstadials. Equus lambei and E. hemionus in the cold Yukon fauna of Gold Run Creek also appear at Berclair Terrace, Texas, during the same mid- Wisconsin interval. See text for discussion. Postulated early entry of a more generalized bifacial and flake tool kit during the mid- Wisconsin (upper) and the mammoth-hunting specialist blade culture during Two Creeks time (lower) may have made contact at this later time and influenced the origin of Clovis tool kits. Adapted from Müller-Beck (1966). Key: 1. Ice extensions, 2. Mousteroid industries, 3. Pebble tool traditions, 4. Com- plexes of bifacial traditions and points. 5. Aurignacoid traditions.




4'^» J ^§8* áj^$°s š 1 1 : 1 : : : : :

TWO CREEKS?) ' A ' 5

■ s ' ť r A ' ittcrrù rrfZy?.



148 Mario Picharão

ciirred during the LGM is taken into account. Reading from the left, the southern Plains short-horned Bison antiquus (FAD ca. 30,000 yr B.P.) appears while the giant Steppe B. priscus is still present both north and south of the ice sheets. At Gold Run Creek a cold fauna predominates with Mammuthus primigenius , Rangifer , B. priscus , Alces and Bootherium together with two Asiatic horses: Equus lambei and E. hemionus . The only southern forms are Camelops , Castoroides with Mammut , Arc- todus and Taxidea. But these forms could well be relicts in the Beringian refuge that had arrived before Wisconsin time. Dates range from 39,900 - 22,000 yr B.P. for B. pricus and 32,250 yr B.P. for M. primigenius (Harington & Clulow 1973), and the fauna can be referred to the Saiga cold steppe province (Fig. 1, upper). This neat arrangement is upset however by a date of 29,300 yr B.P. for the southern Plains Mammuthus columbi at Old Crow to the north (Harington 1980).

At Old Crow Loc.-l 1 Bison priscus is dated at 12,460 to 11,910 yr B.P. (Wilson 1996). Other forms with a minimum date of 20,000 years like Camelops , Platy go - nus , Megalonyx and M. columbi reached Alaska (Kurten & Anderson 1980), but did not cross into Siberia whereas Siberian forms like Saiga and E. hemionus entered Beringia. From this it is possible to suggest that the Camelops fauna had dispersed as far north as Alaska during the mid- Wisconsin Interstadial and the newly arrived Amerinds (Amurians?) would have followed the fauna southward. Evidence of a most direct connection comes from Berclair, Texas, dated to mid- Wisconsin (Lun- delius 1972), which has the very same Camelops assemblage, and in addition the migrants Equus lambei and E. hemionus (Pichardo, in press).

Two mammoth kills at Iztapan, Valley of Mexico, contain both stemmed and leaf- shaped points and lie below the PWA ash marker (coarse pumice with andesite) dated to 14,450 yr B.P. (Pichardo 2000b). The Camelops fauna was still extant in Central Mexico at this date in Tocuila (a village just north of the town of Texcoco, Fig. 4) where remains of seven mammoths, Camelops , horses and bison were found (horses and bison still unidentified; Morett et al. (1998), Siebe et al. (1999)).

Fig. 2., lower, illustrates Müller-Beck's clear understanding of the possible 'back- wash' movement of the earlier stemmed/leaf point culture coming into contact with the arriving Aurignacoid blade culture during the Two Creeks Interstadial. As al- ready noted this is when the Great Basin generalized foragers could have been influenced by the single-species hunting of Aurignacoid groups. Presumably this cultural contact produced the 'blitz' dispersal of the Clovis hunters proposed by Martin (1973).

But the evidence from Iztapan/Tocuila demonstrates that species-selective hunting may have occurred independently and earlier when environmental conditions offered the opportunity. Further, laurel-leaf and stemmed points were also used opportunistically in the multiple environmental settings found in South America. In the western highlands leaf points are associated with mastodonts from Monte Verde, Chile, 12,500 yr B.P. (Meitzer et al. 1997) to the sites in Venezuela and Colombia, whereas in Brazil stemmed bifacial points appear at Pedra Pintada associated with a more generalized foraging culture from 1 1,145 yr B.P. (Roosevelt et al 1996).

At Old Crow, Loc.-l 1, Bison priscus was dated at 12,400 - 11,900 yr B.P. (Wilson 1996). But the Great Plains area was wooded with conifer forest between 20,000 - 18,000 yr B.P. and prevented southern grazers easy access to the north. The




Great Basin on the other hand was covered by open woodland from about 35° North latitude and extended southward as far as the Mexican Plateau. North of 35° up to the ice border at ca. 45° North were patches of conifer forest and steppe tundra (McDo- nald 1984).

Consequently, it seems likely that elements of the Camelops fauna moved northward from the Great Basin along the route suggested by Heine (1998) west of the Rockies. The short-horned Plains Bison antiquus, however, never reached the Yukon and was able to reach Central Alberta only by 1 1,370 yr B.P. (Wilson 1996) after the forest barrier was reduced during Two Creeks time. At Old Crow, in Fig. 2, lower, the Camelops faunal elements, including Mammuthus columbi, are listed only by inference since precise dates are not available.

This then is a plausible preface to the discussion of the Central Mexican sites below. As indicated above, the bio- and chronostratigraphic approach is followed because it offers empirical data upon which to anchor any interpretations, which can easily become speculative on more loosely handled archeological data.

Central Mexico

An inventory of Paleoindian sites will not be presented here. Only the three classic areas located in Fig. 3 will be considered, 1. Lake Texcoco Basin and Valley of Tequixquiac, 2. Valsequillo, 3. Lake Chapala, with reference to morphostratigraphy, chronostratigraphy and biostratigraphy. The illustrations will serve as a guide regarding locations, sections and dates.

Lake Texcoco Basin and Tequixquiac This is the classic area of Mexican prehistoric studies going back to the late 19th Century. The modern period of study began in the late 1940's and early 1950's.

"" *

i

^ L w j; - - 1

Fig. 3. The Central Plateau (dashed line) contained many lake filled basins in the Pleistocene (shaded areas), often surrounded by volcanoes (black dots: active, white dots: extinct). The three classic areas of Mexican prehistory shown are Valsequillo, Tequixquiac/Mexico (Lake Texcoco Basin) and Lake Chapala. Adapted from West (1964).



150 Mario Pichardo

Recognition of the value of tephra for chronostratigraphic control came from 1960's (Mooser & Rul 1961) and applied directly to the relative dating of prehistoric sites like El Peñón, and mammoth locations at Iztapan and Tepexpan. A first 14C date was published for the important PWA tephra marker at the Tlapacoya archeological site (Mooser 1967). By 1986» a dated tephra sequence was elaborated (Lambert 1986) and correlated with a series of lake beaches at Tlapacoya (Flores-Diaz 1986).

The 1961 mammoth-site plot for the Lake Texcoco Basin (Pichardo et al. 1961) was updated twenty-five years later (Lorenzo & Mirambell 1986, Silva-Barcenas 1987). But although these later summaries published a few 14C dates for some of the latest finds, no attempt was made at a tephra correlation for all of the Lake Texcoco mammoths. It was not until the 1990's that a new surge of tephra studies appeared, focused primarily on paleo-environmental studies of the Lake Chalco sub-basin (see Fig. 4 and Lozano-Garcia et al. 1993, Ortega-Guerrero & Newton 1998, Caballero & Ortega-Guerrero 1998).

The importance of an updated mammoth taxonomy for prehistoric correlation in the Central Mexican Plateau has been recognized. Collection of specimens under a stratigraphically controlled tephra sequence, as well as measuring and plotting of mammoth molars to identify species constitute an essential first step for any future studies (Pichardo 2001).

Morpho stratigraphy There is however another long neglected aspect of Central Mexican Prehistory critically in need of review. The impressive amount of morphostratigraphic information compiled by workers during the late 1940's and early 1950's must not be lost. These data have been neglected simply because there were no subsequent studies along these lines. Paleontologists have concluded that the two formational names 'Becerra' and 'Tacubaya' have been used so loosely that they have no formal status, and that interbasinal correlations have not been made (Miller & Carranza-Castañeda 1984, p. 221). At Tequixquiac, Hibbard posed the question of when in a Pleistocene cycle did downcutting and deposition of gravel and sands occur? Since their occurrence is cyclic, can each cycle be explained as having the same cause? (Hibbard 1955, p. 82).

With the advent of tephrachronology it is now possible to begin to answer these questions in the Texcoco/Tequixquiac basins which are both within the perimeter of tephra rain from such volcanic sources as Popocatepetl and even the Toluca volcano. Much information can be obtained from the earlier morphostratigraphic studies of Bryan (1946, 1948), Arellano (1946, 1951) and DeTerra et al. (1949). A preliminary correlation with these studies and the tephra sequence will be discussed below.

Fig. 4 (adapted from DeTerra et al. 1949) illustrates the general topography of the Lake Texcoco Basin and the Valley of Tequixquiac just to the north of the low divide (Fig. 4, B) formed by the Lomas de España which are set between the Sierra de Tepotzotlan to the southwest and the Sierra de Tezontlalpan to the northeast. Also shown is the Valsequillo Valley, to the southeast of the Sierra Nevada (Popo, Izta, Tlaloc volcanoes). The map contains much information but it was deemed necessary in order to locate at least those sites critical to stratigraphie, paleontologie and prehistoric analysis.




" $ ° Kilomcters°

fò (y fo' Kcs ¿/l£Č$!nhj ;m - s - * -

r S

w> fTetepaauiL ^ (y

/ Pò chuca «,***, * ^ S fTetepaauiL ^ / Pò chuca

} t P' ^ ggT J toa/ « Hhtfa } 206A ( J ' Canaî, underground ' V'V f fV,*^ /Or MEXICO CITY V /~' ' ' V Jjj, / |7 ' / 'IP~ Depression contour /j'p£7 V SaiCö /~' i V/V/i ̂ S S'T /O Heights in Pleistocene

?i r /j'p£7 Û& v <3»»«^ . ,

r ( L ^~y Ím

t'0sét*ty£^ )/ csÂntT^. r

i JL. JÍ

ShsSr BeccnÄ? 4 Täfe^ä^ BeccnÄ? . J f

(n U ( V.MAUNCHt; U IVv

y%^

WÀsm^-^^ pu,ebl|V X

^ Çy^j* yCt/m7<rm<asr ^f~~~^ °/83qJ ^

Fig. 4. Topography of Lake Texcoco Basin, with Tequixquiac north of divide-B, and Vals- equillo in Puebla to the southeast of the great Sierra Nevada. Black dots around the lake denote mammoth and other megafauna/artefaet locations, while white dots show other prehistoric sites discussed. X-sites contained Paleoindian remains. See text for discussion. Base map from DeTerra et al. (1949).

The Lake Texcoco Basin is subdivided into six sub-basins from north to south: Lakes Zumpango and Xaltocan, San Cristobal (covered by the word 'Risco'), Tex- coco, Xochimilco and Chalco. Lake Texcoco was the lowest, Zumpango/Xaltocan the highest (6 and 3 meters higher), whereas Lake Chalco stood about 3 meters above Lake Texcoco (Caballero & Ortega-Guerrero 1998, p. 71). The oldest outcrops of Plio-Pleistocene deposits comprise the Tarango Formation. They occur over



152 Mario Picharão

eroded earlier volcanics as extensive alluvial fans in the eastern and western sides of the basin (Mooser 1963, 1990). In the Pleistocene a true valley, open to the south, drained eroded Tarango deposits through two major streams; one flowed from the Zumpango heights along the eastern slopes of the Sierra de Guadalupe past Xochi- milco, while the other ran along the western flank of the Sierra Nevada past Chalco.

At that time, renewed volcanism in the northern end of the basin formed cones like Cerro Gordo, with others southward along an axis connecting with the Sierra de Guadalupe (Fig. 4, A). The géomorphologie history of this early Valley of Mexico is pertinent for an understanding of its relation to the multiplicity of lake basins that covered much of the Central Mexican Plateau during the Pleistocene. That they were often connected by streams has been demonstrated by the presence of related species of Atherinid fishes, genus Chirostoma (Silverfishes, Pescado Blanco), from Lake Chapala in the west to the Llanos de San Juan in Puebla (Barbour 1973) to the east (Fig. 3, Fig. 10, south of Oriental). A high plateau lake ecosystem existed with many parallels to that occupied by the generalized foragers of the stemmed/leaf points tradition in the Great Basin. Both plateaus lie within the Came lops province and shared the same megafauna, with only minor specific differences.

Today the Valley of the Atoyac River is open to the south through Valsequillo. During most of the Pleistocene the Valley of Mexico, also open to the south, permitted easy access to tropical megafauna like the gomphothere Cuvieronius and edentates like glyptodonts and giant sloths. But even today the gentle slopes of the basin fills, as well as the low passes between the southern plateau's edges, makes the southern approaches much less difficult than those on its eastern and western sides (West 1964, p. 55).

Recent work has determined that the final closure of the valley to the south occurred ca. 23,000 yr B.P. (Siebe et al. 1995, Ortega-Guerrero & Newton 1998), caused by a great eruption of the St. Helens type of Popocatepetl. The outpouring lava and debris joined with the east- west axis of the Chichinautzin Range composed of such cones as Ajusco and Cuautzin which had been forming earlier in the Pleis- tocene. The freshening of the Lake Chalco due to increased water input favored overflow into Lake Texcoco (Caballero & Ortega-Guerrero 1998).

Earlier tectonic activity along the Cerro Gordo-Sierra de Guadelupe axis piched- off the two northern sub-basins of Xaltocan and Zumpango and it may have been at this time that they were elevated to levels higher than that of Lake Texcoco. At some point during the Pleistocene communication of the northern sub-basins with the Valley of Tequixquiac must have occurred permitting the Chirostoma fishes to enter the Valley of Mexico drainage systems. The Acatlan stream at Tequixquiac is a minor tributary of the Rio Salado, itself a tributary of the Tula River which even- tually joins the Rio Moctezuma-Panuco trunk that empties into the Gulf of Mexico at Tampico. The northwest wall of the Tequixquiac Valley may have been breached (Arellano 1953); it is known that the Tula River captured the San Juan del Rio River which formerly flowed westward into the Lerma River systems (Tamayo & West 1964, p. 90). Thus, a tectonically active plateau facilitated stream capture and dispersal of Chirostoma fishes across the many lake basins from Chapala to Puebla.

Barbour recognizes that the temporal subsidence of Texcoco Basin makes it difficult to calculate detailed oscillations of the lake, but points out that in a circum- scribed area, strata of commensurate age will be at approximately the same level




(Barbour 1973, p. 540). DeTerra (1949, p. 28) found that while the Tequixquiac/ Texcoco Basin divide (Fig. 4, B) has suffered uplift at a greater rate than the movement assumed for the Totolzingo-Tepexpan lake beaches, the high level of earlier water-laid deposits in the latter area indicate a higher lake level than during the succeeding El Risco beach substage. At Tequixquiac he found that Lower Becerra deposits are clayey suggesting deposition in quiet water, possibly a lagoon of an

o (OOO ÎOOO ' I MCTtM

«A . I I

Mammuthus columbi . % PU*»*T€ OSI OAU.O '

PÑl e*"*«. Bison antiquus y <<>

Jb> • * ' £;<^mexicanus V Bison,chaneyi ^

h* ^ T°' T^rríx 'S*N HATfO. i '' ^ 'S*N HATfO. J V' 'S*N ' vn'

HATfO. J V' > W1 - - - n'<*

-

1

r

I =^J 'V' M ( r

I >ilS i'

M (

r'' pr

' if?) '4

•- - ,mzy* li1 - I NEW AND 0LD TUNNELS

IJ

Fig. 5. Map view and section (at artefact location-X) of Tequixquiac deposits. T, Tacabuya Formation outcrops; B, Becerra deposits. Numbers represent Hibbard's collecting stations and locations where some species were found. Section contains Lower Becerra (1, 2), Upper Becerra (3, 4, 5), Totolzingo dark sand (6) and dark earth with potsherds (7). Adapted from DeTerra (1949) and Hibbard (1955).



154 Mario Pichardo

Upper AcatlAn Barranca Lake Beaches Near Totolzlngo CHALCC Near Tequixquiac El Risco beaches beach Mammuthus -, - . --x rTotolzmgo eoil «níl I 4a g'l i i J - . . . i -,

- . ^ --x L rTotolzmgo eoil «níl . I Anññi jeffersoni 1 j J if" | |

i Callàie III ̂ ' L Zacatenco 2248 m II 12263 . m tbU1 5 b - ■ • R /inrf/7w?/rUpper Alluvial Silts ' beach/ i » / a R a /inrf/7w?/rUpper cnleyi Lower ^Young Sand

Alluvial Becerra and

Silts ' XCT^n,1"! r®02

i ̂ /

/ Old ?3

a Lower Sand and Grave] ¿t-Xv^T* r®02 ' j f!pr„r_ ^ ~ j I "VcaMche II i503 ' s-240"1 / j

~~ Old Becerra YoUng Becerra

Tacubaya

î"11 fB03. Hondo section

Fig. 6. Section of Acatlan Barranca, Tequixquiac (upper left), shows mammoth and bison species succession. The Upper Becerra is divided by an erosional surface into lower sands and gravel and upper alluvial silts. The high energy system effective in the lower sand and gravel appears to correlate with the high Risco-I beach at Totolzingo (upper right) and beach 5b at Tlapacoya. The PWA tephra dates to ca. 14,450 yr B.P. below Risco-III isochron sands. Later deposits are discussed in the text. Below, the Rio Hondo section also illustrates climatic events during the terminal Pleistocene. Roman numerals represent morphostratigraphic units. See text for discussion. Upper left and below adapted from DeTerra et al. (1949). Upper right is a composite section from DeTerra (1949), Mooser & Rul (1961) and Flores-Diaz (1986).

adjoining lake. Since there is no physiographic enclosure to the north of such a lake, Barbour suggests that the headward eroding Panuco River could have destroyed the lake and its sediments (Barbour 1973, p. 539).

By contrast, the Younger Becerra sediments of cross-bedded sands, gravel and cobbles reflect a phase of stream aggradation with temporary torrential currents washing the hillsides. It is in these cross-bedded sands and gravels that fossils and human artefacts are found. The top layers of the Upper Becerra represent the fines or overbank deposits of a later period. Below the Becerra, brown Tacubaya clay represents the remnants of a caliche-coated pedalfer soil sheet covering the slope of a previous valley which was subsequently buried by Lower Becerra lake deposits (Fig. 5, map view and section).

Correlation of the Totolzingo-Tepexpan highest (Risco-I) beach (2263-2265 m, DeTerra 1949, p. 23) with Tlapacoya beach 5b dated ca. 22,000 yr B.P. is important. It represents an oscillation raising the lake level that postdates the Tlapacoya beach 4a which formed during the overflow of water into Lake Texcoco caused by the cataclysmic eruption of Popo (Fig. 6, upper right, and Flores-Diaz 1986, Fig. 48). This also agrees with DeTerra's observations that the only evidence of a high energy fluvial system at Tequixquiac is found at the transit from the Old Becerra lake clays to the torrential cross-bedded sands and gravels of the Upper Becerra (Fig. 6, upper




.__AÛAkl i ZTAPAN _ Estadio p-, i . I4r Co9eS _nac Tequixquiac .__AÛAkl i ZTAPAN H _ Olřmplco rSHALCO CHALCO

p-, psi i . I4r Co9eS _nac

t rSHALCO CHALCO J {yrB.J?) ÀCATLAN BARRANCA il' 1 ( _ - ^Totolzingo S

( 1 _ - 2 mm

m uni^ Calidie III , ji T73T7T. UTP 3 Unifacial___ ™ Alluvial Silts

Eöxki -PWA - y v-** 12800 - H - li'.V/î artefacts __ ™ 0 ^ Lower Sand and Gravel Eöxki Wg£S>!

-PWA - I

- H - A

li'.V/î SÉâ r

__ *¡¡¡^F*»âlÍcKe H

yjfff as««« I

^HI Ig; t V Old Becerra

T/ «; B Vlla4 B"7'450

* VIII I ¡ŤŤŤS - - IX =====--21,600 J

ŽSŽŽ "22,720

' ¿trati- units tepnra layers

Fig. 7. Correlation of Lake Texeoco sections at Iztapan (north), Estadio Olimpico (west; dots are soil horizons), and Chalco (south) with Tequixquiac. Chalco tephra-X closely correlates with Popo's great St. Helens-type eruption ca. 23,000 yr B.P., and with the only evidence of high energy fluvial sands and gravels at Tequixquiac. UTP (Upper Toluca Pumice) and PWA (Coarse Pumice with Andesite) are important tephra markers, and the latter dates the Iztapan mammoth kills at older than 14,450 yr B.P. Adapted from Mooser & Rul (1961), Mooser (1967), Lozano-Garcia et al. (1993), Caballero & Ortega-Gerrero (1998) and DeTerra et al. (1949).

left, Fig. 7, right). I find no other morphostratigraphic evidence for a high energy system which could have been responsible, except from overflow of Lake Zumpan- go or from isostatic adjustment to redistribution of material, resulting from erosion, transport and deposition (c.f. Bridgland 2000, p. 1298). In either case, the result would be stream rejuvenation and a high energy system acting on the Tequixquiac Valley. Provisionally, on morphostratigraphic grounds, the gravels, fossils, and artefacts collected date to the mid- Wisconsin Interstadial correlated with the fBol soil found on the slopes of the Toluca, Popo, Izta and Malinche volcanoes (Heine 1978, 1984, Pichardo 1999).

Paleontology Provisional support for a mid- Wisconsin Interstadial date for the base of the Upper Becerra at Tequixquiac may come from study of megafauna species succession (Pichardo 1999, 2001). The presence of giant Bison priscus , Mammuthus columbi and unifacial tools in the basal gravels contrasts with short horned Bison antiquus and morphologically derived Mammuthus cf. jeffersoni in the upper silts. The ob-



156 Mario Pichardo

vious caveats are questions like the temporal span of B. priscus may have been extended in Central Mexico, and that mammoth taxonomy is only at a preliminary stage (Pichardo 2001).

Compared to Tequixquiac and Valsequillo, megafaunal remains other than mammoths are scarce along the shores and slopes of the Texcoco Basin. They are best sampled in the following locations described in clockwise direction in Fig. 4. Three fundamental sources are Alvarez (1965, 1986) and Silva-Barcenas (1969), and the summary by Lorenzo & Mirambell (1986). If taxonomie identification needs citing the source is listed (e.g. Sta. Fé: Hay 1925). In order to avoid repetition, sources are designed by letters in parentheses: (A) Alvarez, (AC) Arroyo-Cabrales (in Morett et al. 1998), (C) del Castillo, (D) DeTerra, (H) Hay, (HP) Herrera (Pichardo, in press), (LM) Lorenzo & Mirambell, (M) McGrew (in DeTerra 1949, 1959), (MC) Mc- Donald (1981), (S) Silva-Barcenas.

Camelops hesternus (LM) has been reported at Sta. Lucia-I, with Smilodon , and at Sta. Lucia-II. Bison sp. and Equus cf. semiplicatus (M) were found in the calichized fBol soil on slope deposits north of Totolzingo (Fig. 6, upper right, Caliche-II) which descend to a level of 2300 m. They cover Lower Becerra clay, laminated silt and rootlets suggesting lagoon deposits (DeTerra 1949, p. 26). The highest (Risco-I) beach indicates renewed discharge into Lake Texcoco since it rests on the Lower Becerra eroded slope. This interval represents an oscillation of the high energy system initiated by the Popo eruption and provides telecorrelation with the basal gravels of the Upper Becerra at Tequixquiac (Figs. 6 and 7).

After this period of high energy there was a progressive drop in lake level, with oscillations most notable in the deeper Chalco sub-basin (Flores-Diaz 1986, Fig. 48). In the northern part, at Totolzingo, the Risco-II beach fell to 2257 m or 10 m below Risco-I and is the lowest beach found in the Totolzingo-Tepexpan area. Risco-III occurs at El Risco on the western shore (Fig. 4). The Iztapan mammoths were found below Risco-III isochron containing the PWA tephra marker (Fig. 6, upper right; Fig. 7, left). PWA, coarse pumice with andesite, is sometimes found at two proximate levels (e. g. Tlapacoya) dated ca. 14,770 yr B.P. for T1 and 14,450 yr B.P. for T2 (Ortega-Guerrero & Newton 1998).

Camelops hesternus , Equus sp. and Bison sp. (AC) were found in the Tocuila Lahar. Bison priscus is recorded in a sand pit at Chicoalapan (MC) together with Camelops and mammoth about 1.6 km from the human skull (D). Camelops hesternus , Bison sp. and Glyptotherium (LM) are at Chimalhuacan, and the giant sloth Glossotherium (LM) occurs at Reyes La Paz-I in a level between the UTP marker (Upper Toluca Pumice) dated ca. 12.800 yr B.B. and the T1 or lower PWA marker at 14,770 yr B.P. At Tlapacoya (A) the levels of the following species have been dated: Megalonyx sp. 33,200 - 23,000 yr B.P., Equus mexicanus , same. E. semiplicatus only at 33,200 yr B.P. Camelops hesternus 33,000 - 27,000 and 14,770 yr B.P. Antilocaprid at 20,300 yr B.P. and Bison cf. latifrons 33,150 yr B.P.

At Xico (HP) a human mandible found by Herrera (1893) was associated with a very mineralized horse skull identified by Villada as 4 Equus excelsus ' (= E. mexicanus ; Pichardo, in press). At St. Fé on the western side of the basin Mammut americanum is recorded (H). Clays from Mexico city building foundations (S) have yielded Bison sp., Equus sp. and camel, and near La Villa (S and C) Glossotherium , Equus sp. and camel are recorded.




1. Mammoths

Virtually all the above sites contained Mammuthus also, and many other mammoths with or without associated artefacts have been recorded (Pichardo et al. 1961, Silva- Barcenas 1987). The chronologic range of most of the megafauna thus extends in the Texcoco Basin at least until the 14,450 yr B.P. of the Tocuila fossils. The San Bartolo Atepehuacan mammoth (9,661 yr B.P.), Venta del Carpio (near Totolzingo, Mooser & Rul 1961), Reyes La Paz-I and Sta. Lucia-II (1 1,170 yr B.P.) are all younger than the PWA markers.

Guenther (1973, p. 158) points out that in the Tepexpan sample the molars had evolved a greater number of plates (comparable to M. jeffersoni) and display linear grooves or cracks (hypoplasia) suggesting that a more stressful regime with marked seasonality and more limited nourishment had occurred during the terminal Pleis- tocene stages of the Lake Texcoco Basin. These derived morphologic features carry taxonomie weight (valence) and are found in the molars of M. falconeri (Villada 1903) from Tequixquiac, without stratigraphie data, which I tentatively assigned to the top of the Upper Becerra (Pichardo 2001, p. 48). Presumably these traits also occur in the mammoth found in the Upper Bacerra silts by Hibbard (1955, p. 50), which Madden (1981, p. 267) refers to M. jeffersoni (Fig. 6, upper left; Fig. 8). Much work is needed to begin to develop, and correct, the preliminary mammoth taxon-

Mammuthus jeffersoni columbi ? M* columbi felici s

0 10 CM

Fig. 8. The three mammoth species provisionally accepted as present in the Central Mexican Plateau during the late Pleistocene. Closely compacted molar plates assigned to M. jeffersoni may possibly represent parallel evolution as M. c.felicis in the Mexican Plateau. The unifacial flake point imbedded in the M. imperator mandible is tentatively assigned a mid- Wisconsin date. See text for discussion. Adapted from Guenther (1973).



158 Mario Pichardo

omy which I have proposed (Pichardo 2001) and hopefully will encourage students to undertake this task. Fig. 8 illustrates molars of the three species usually considered to be present in the late Pleistocene of the Mexican Plateau.

2. Horses The horses also have value as index-fossils, both ecologically and chronostratigra- phically, as demonstrated above through the correlation of Beringean Equus lambei and E. hemionus found in mid- Wisconsin deposits also at Berclair, Texas. A preliminary study (Pichardo 2000a) showed that only three species have been taxono-

VALSEQUILLO

conve

francisai

Fig. 9. The three late Pleistocene horse species of the Central Mexican Plateau which have been established taxonomically on the basis of relatively abundant fossils, primarily from Valsequillo and Tequixquiac. The large Equus mexicanus is so far only recorded from mid- Wisconsin sediments, while E. conversidens and E. francisci last at least to Hueyatlaco level E, where a semi-articulated horse was associated with a Lerma point. From Pichardo (2000a).




mically established during the LGM in Central Mexico, a large E. mexicanus , medium E. corner sidens , and smaller E.francisci (Fig. 9). A more recent taxonomie revision of North American Pleistocene horses (Azzaroli 1998) permits a more detailed sorting of the species present in Paleoindian sites throughout the Americas (Pichardo, in press). Sites in the Southwest are now known to include a large Equus ferus , and the smaller E. lambei and E. hemionus. Further, E. mexicanus is removed from synonymy with E . pacificus , restricting its geographic range to the Central Mexican Plateau.

As discussed below, Valsequillo sediments have so far not yielded E. mexicanus remains younger than Faunal Zone-2, a mid- Wisconsin isochron (e. g., 26,000 ± 530 yr B.P., KI-266 in Guenther 1973; Pichardo 2000b). At Tequixquiac E. mexicanus was also found at the base of the Upper Becerra (Fig. 5, between Locs. 2 and 3) by Hibbard (1955, p. 72), and at Barranca del Muerto, without stratigraphie data (Az- zaroli 1998). In the Texcoco Basin no horse remains have been identified to species except for Equus mexicanus at Tlapacoya (mid- Wisconsin age) and possible references to E. semiplicatus at Tlapacoya and Totolzingo. The only dated site with horse remains is Tocuila, but species are not yet identified. Of special interest is the association of E. mexicanus with the human mandible at Xico. Students are urged to obtain tephra dates for these sediments which may help to date a possibly mid- Wisconsin Paleoindian.

3. Bison The presence of short-horned Bison antiquus at mid- Wisconsin levels of Barranca Caulapan in Valsequillo restored credibility to the original association of tools and megafauna (Pichardo 1999, 2000b) since Uranium- series dates concur with 14C dates at this site. Illinoian-age U-series dates from the cultural locations along the edge of the reservoir indicate either redeposition of fossils or contamination from ground water (Pichardo 2000b). Since the FAD for B. antiquus is ca. 30,000 yr B.P., the bison sequence at Tequixquiac needs further study. It may be that the short- horned bison preferred the open river valleys of Tequixquiac and Valsequillo, whereas the large B. priscus found in Upper Becerra basal gravels at Tequixquiac (and at Chicoloapan in the Texcoco Basin) was a relict of the previous lagoonal phase suggested by the Lower Becerra clays.

So far only species of these three taxonomie groups have shown to have value as index-fossils. The remainder of the fauna has received even less attention and is poorly known taxonomically. For a more detailed taxonomie list see Pichardo (1997, 1999), in which E. mexicanus must be returned to replace

' E . pacificus '

Becerra Stratotype and correlations The problem of defining the upper and lower boundaries of the Becerra Formation can best be resolved by comparison of the two morphostratigraphic divisions proposed by Bryan (1946) and Arellano (1951) with the tephra sequence being developed at Lake Chalco. As outlined by Arellano (1951), the stratotype section is the alluvial fan facies found at Ciudad Deportes, about 3 km south of Tacubaya, within the triangle formed by the Mexico City streets Eje-5 Sur, Eje-6 Sur and Avenida Insurgentes. Becerra Creek had been captured by Rio Piedad at least by 1889 (Felix



160 Mario Pichardo

& Lenk 1889, Plate 1). During the late Pleistocene, however, it deposited over 16 m of alluvial fan deposits on the southwestern shore of Lake Texcoco (Arellano 1951, p. 56). Two kilometres upstream Becerra Creek narrows exposing about 2 m of Becerra sediments, their base inferred from the reddish Tacubaya outcrops in the slopes. Several kilometers upstream, Becerra alluvium overlies Tacubaya with coarse sands, gravels and finer loams 5-8 m thick, but subdivision of the Becerra was not attempted.

Within the alluvial section at the stratotype a prominent marker of 'fine black sand and well rounded andesite pumice pebbles' and fossils was named the Armenta Horizon (Arellano 1951). It is about 0.5 m thick at the western end of the section but develops into 2 m of peat, clay and sand 600 m to the east. Its 2242 m elevation suggests possible correlation with Risco-III beach (Fig. 6) and with the fBo2 soil dated 12,000 - 18,000 yr B.P. (Heine 1978, 1984). But wood from the pumitic sands, associated with mammoth and horse, dated older than 16,000 yr B.P. (C-204) whereas peat 500 m east gave a date of 11,003 ± 500 yr B.P. (Libby 1955, p. 129). If these dates stand, it seems likely that the pumice with andesite gravel represents reworked PWA tephra of either T1 (14,770 yr B.P.) or T2 (14,450 yr B.P.) age. Subdivision of the Becerra into two parts by the Armenta Horizon as proposed by Bryan (1946) and Arellano (1951) brings up some questions.

The Armenta Horizon, or PWA?, was not observed at upstream Becerra Creek (Arellano 1951, p. 57). The vertical section of the entire Becerra Formation is over 16 m at the stratotype, the alluvial fan. Arellano notes that if the base of the Becerra lacustrine facies is taken where the limonitic or iron-stained character of sediments referred to Tacubaya begin, the total thickness cannot exceed 3-5 m because of the wind-borne source of the fine sediments. Upstream Becerra Creek exposes only 2 m of Becerra overlying slope Tacubaya outcrops, and up to 5-8 m further upstream.

At Totolzingo the total Becerra (Older clays and Risco beach sands) section is 11-13 m (DeTerra 1949, p. 25). At Tequixquiac, as at Totolzingo, up to 5.6 m of Tacubaya clay coated with caliche appears to lie below Older Becerra fill in the manner of a fossil soil sheet on the slopes of a previous valley. Average thickness of the Younger Becerra is 8-10 m, but the Older Becerra is here much thicker than on the Totolzingo-Tepexpan hill slopes (DeTerra 1949, p. 87) and is calculated to be 21 m thick (from DeTerra 1949, Fig. 8). Thus the total Becerra at Tequixquiac is some 30 m thick, but outcrops expose various depths in sections, e. g., at the artefact site (X, in map and section of Fig. 5) it attains 8.75 m, and 7.4 m at Mazapan Barranca near Teotihuacan (Fig. 4).

In sum, of the up to 30 m of total Becerra only some 10 m of Upper Becerra are recorded. DeTerra observed depositional hiatuses, or erosional disconformities, between the Tacubaya/Becerra and between Lower and Upper Becerra deposits. Mor- phostratigraphy at Totolzingo and at Tequixquiac reveals possible uplift, but also a long erosional phase represented by the slope of calichized Tacubaya sediments at Tequixquiac which form the depositional trough over which Becerra clays were deposited.

The proposal of early workers that the Armenta Horizon divides Lower and Upper Becerra sediments can be discarded. Recent work indicates rather that the division had a tectonic origin and is represented by higher lake levels, and which coincides with mid- Wisconsin time. Contrary to earlier observations lacustrine clays




at Chalco extend to a depth of ca. 26 m (Fig. 7, Chalco Core-B; Caballero & Ortega- Guerrero 1998) and brown silts occur throughout the section. A dusky red silt is recorded in Core-T from the western lake shore south of the Sierra de Guadalupe (Ortega-Guerrero & Newton 1998). It lies abut 6 m above tephra XI dated 26,000 - 27,000 yr B.P. The Tlahuac, or Tephra-XII, older than 34,000 yr B.P. lies at 18 m depth in Chalco Core-B, but only at about 5 m at the Estadio Olimpico section which is about 10 km east of the Becerra stratotype on the western shore (Fig. 7). Apparently the longer sections of the Chalco Lake cores reflect its greater depth and subsidence.

Determination of the Becerra/Tacubaya contact on the basis of iron-stained sediments in the latter must be reconsidered in view of the above. Arellano (1951, 1953) proposed interbasinal telecorrelations ranging into the states of Hidalgo and Oaxaca, and has been followed by some paleontologists who refer similar red-beds containing the Cedazo fauna in the state of Aguascalientes to the Tacubaya (Mooser & Dalquest 1975). They estimated a possible temporal range from Aftonian to Sanga- mon Interglacial ages (or latest Irvingtonian to Late Rancholabrean Land Mammal Ages). More recent work supports this time but reports Aluralagus of Lower Irving- tonian, or Lower Pleistocene, ca. 1.5 my. Upper units are referred to Rancholabrean age, ca. 0.2 my to about 10,000 yr B.P. (Montellano 1989). Montellano's upper lithostratigraphic unit contains Bison priscus (McDonald 1981). The horses appear consistent with a Sangamon age since Equus semiplicatus ranges to late Illinoian at Hay Springs (Azzaroli 1998) and its metapodials occur at Cedazo. Equus niobrar- ensis is also present at both sites and the absence of any archaic horse like E. crenidens (from undetermined strata at Tequixquiac) favors a late Rancholabrean age for Montellano's Unit 3.

To conclude, it is evident that the diagnostic criterion of limonitic or pedalfer soils can be applied to the wetter and warmer conditions at different times and places. Consequently, until a tephra sequence for the Texcoco Basin and Tequixquiac Valley can be established, beginning with the stratotype section at Becerra Creek's alluvial fan, these questions cannot be resolved. The prospects for renewed field work are great for students entering this field. Figs. 6 and 7 summarize the agreement between known morphostratigraphic and tephrachronologic work.

Fig. 6, lower, indicates DeTerra's morphostratigraphic analysis of the Rio Hondo section (see map Fig. 4) and, above right, the position of Zacatenco beach and its correlate to Totolzingo soil. Stratigraphie units in the Rio Hondo section include post-Totolzingo Terrace-IV, or Rio Hondo Terrace, which contains archaic burials, followed by cutting of Terrace-II, or Los Remedios Terrace, containing Teotihuacan and Azted ceramics. These terraces were preceded by erosion phases III and V, whereas the long pronounced slope of erosion phase VII suggests its formation extended into the preceding phase VIII of desiccation (calichized fBo3 soil) and by the falling lake level of Risco-III beach (DeTerra 1949, pp. 57-59).

Valsequlllo Valley Previous work in the Valley of the Atoyac River of Valsequillo, Puebla, has been recently discussed in the Valsequillo Biostratigraphy Series (Picharo 1997, 1999, 2000a, 2000b, 2001). Fig. 10 illustrates important reference points which include the



162 Mario Pichardo

98° 30' 96°00' 97°50'

' MEx,C0 1 J Arto o K V f J 19° /^y/} '«W* J

^HjÁLOC Vj 1 fó° Fr'° Orientai /V _

.-«tuco S 1 I S >' îT'Jítí/ ' i .-«tuco t,,r ' r, AìhuatNÌ v

I S >' --.í/f îT'Jítí/

/lì i

Uýf6m r,

xX ^ i ^ S #PQ»0 <!• Corn» ji C %l ^ {

£- °° ÍGS/SSS*"- J^7 Xra plco5?!o°mRIZAB^ - {

°° Ccfàl, «¿^ ^ ^ ' 2,0° ( TecamAchalco*1 ^ « j '

w 0 25 *-50 KILOMETRES rs J %> ř2°° 1 ■ I » ■ i I - *' rs v J ̂ Tehuacan'v- ( eowrooi» imtcbvai: iqóo MCTwt« if < 'l > • ^

Fig. 10. The Valsequillo Reservoir east of the Sierra Nevada and south of La Malinche volcano. Three other fossil locations discussed in text are Tlanepantla, Tecamachalco and Tehuacan. Adapted from Steen-Mclntyre et al. (1981, after Tichy [1968]).

Llanos de Puebla dried out Pleistocene lake flats south of Oriental, the Valsequillo Reservoir, also a Pleistocene lake basin, and three Pleistocene megafauna sites at Tlanepantla (Malde 1978, p. 303), Tecamachalco which contains Cuvieronius and is the type-site for Mammuthus felicis Freudenberg (included in the M. jeffersoni hypodigm, Pichardo 2001), and Tehuacan, where Cuvieronius is also recorded, lies in the valley of a tributary of the Papaloapan River (Fig. 3) which leads to the southern Sierras and lowland tropics. Cuvieronius remains have been found some 100 km southwest of Tehuacan near Huajuapan, state of Oaxaca. The nearby Yolo- mecatl site (Doutt & Black 1962) has provided the most southern record of Equus mexicanus (photo courtesy of Dr. Mary Dawson, Carnegie Museum).

Fig. 1 1 shows the principal Valsequillo collecting sites of Juan Armenia, Ekke W. Guenther, and the Smithsonian team's 1966 field season, as well as the archeological sites. Two 14C dates, from Totimehuacan and Caulapan, for the Faunal Zone-2 place it in the mid- Wisconsin Interstadial and accord with Uranium- series date of 21,000 yr B.P. (M-B-6) also from the mid-Caulapan level. Erratic older U-series dates were taken at the El Horno and Hueyatlaco archeological sites. These are located at the water edge of he Reservoir and probably represent either redeposition of fossils or contamination from ground water (Pichardo 2000b).

A generalized stratigraphy of Valsequillo was provided by Bunde (1973) and of the Hueyatlaco site by Malde (in Steen-Mclntyre et al. 1981). Hueyatlaco was the




96* 15* 10* I I

I r

^

i

^

^^*^^»LM*xtcqno

«id Surf

I

^/L^/^°n

Boltoi ar

' h 26,000 ±530 jf V *) / (KI-266) X ' J Totimehuceon o oinnnîcnrt 500 X } VY J

Atepitzingo /e" o

^1:™ oinnnîcnrt * 500

(L Mm Atepitzingo

Â<r (M"B"6) zt y^Vv ARENILLAS '¿Sl CT o> 21,850 ± 850

*</*^7/ ^ CW'1^95)

-2»2vr ^ZL/^ /(r Tecamachalco - ̂ ° 2 4 H íSÀ

Fig. 11. Valsequillo fossil collecting sites, including archeological sites at El Horno, Hueyat- laco, Tecacaxco, Mirador and Caulapan. 14C dates from Totimehuacan and Caulapan assign Faunal Zone-2 to the mid-Wisconsin and accord with U-series date (M-B-6) also from Cau- lapan. Other erratic U-series and Fission-track dates from El Horno and Hueyatlaco likely resulted from redeposition of fossils or from ground water contamination. Letters indicate species with possible index-fossil value. B, Bison antiquus , C, Mammuthus columbi , CV, Cuvieronius , GB, Giant Bison priscus, H, Equus mexicanas, I, Mammuthus imperator, J, M. jeffers oni, M, Mammut americanum , MIN, Camelops minidokae , S, Smilodon gracilis. Adapted from Armenta (1978).

only site where an internal stratigraphy was developed by mapping a sequence of stream channel gravels (Fig. 12). But a more detailed stratigraphy is necessary in order to sort out the species succession at Valsequillo. Outcrops of possibly Illinoian age deposits are suggested in the Arenillas area by the presence of Cuvieronius , Smilodon gracilis with a LAD (last appearance date) of mid-Irvingtonian ca. 0.86 my, Mammuthus imperator with a presumed LAD of ca. 0.2 my (Madden 1981) and Camelops minidokae to the Sangamon Interglacial ca. 0.1 my. However, species survival in Central Mexico cannot be ruled out.

Cuvieronius is recorded in the mid- Wisconsin Ingleside, Texas, site (Lundelius 1972) associated with Bison antiquus , and is present at Crystal River, Florida, at 14,320 ± 170 yr B.P. (Pichardo 2001). Renewed paleontological collecting at Val-



164 Mario Picharão

BUNDE ÖU Ut HEINE 103 MALDE BUNDE ÖU Ut Cornwall HUEYATLACO rr-rr Biorm 8K ÍB03 Irwin- Williams AL „„ iahar imaunche)

TETELA HUEYATLACO Jr..7 nmasran -Ash . . V > i i eioTiiE

h0RNB¿AM0E 2 1 l'IT íp22L_ F. " J *r ~ /

" ~ - . . . . T - - / artefacts toiuquiuo-ash

^^^TOlUQUlllO-ASH ^

Fig. 12. Valsequillo sections at Tetela, Hueyatlaco, and Loc. 103 20m south. An erosional unconformity (U) separates lower Hueyatlaco sediments containing unfacial flake tools, from the upper sediments with only bifacial tools. Faunal Zone-2 outcrops at Loc. 103 at a level just above and below the unconformity and was dated to ca. 23K (= 23,000 yr B.P.) at other sites. Malde's (1978) recalibration of the archeological site's deposits is here given tentative correlation with those of Loc. 103. Bunde's heavy mineral sequence for Valsequillo deposits gives support to correlation of Cornwall's pedological study of Hueyatlaco in which the cultural levels lie within Bunde's biotite zone above the unconformity. Level-I at Hueyatlaco was not found by Cornwall's inspection because of the seasonal flooding of this site, but it lies below the unconformity and thus in Bunde's hypersthene zone. The lense-E inserted into Cornwall's section between clay levels D-F represents the channel gravels where the horses and Lerma point were found. See text for discussion. Data from Pichardo (2000b), Cornwall (1971), Irwin- Williams (1967, 1978), Malde (1978, in Steen-Mclntyre et al. [1981]), Bunde (1973), Heine (1978, 1989 for Malinche volcano soil dates).

sequillo (Cabral & Castillo 1997) and the report on the sample collected by the Smithsonian team in 1966 (Graham, in preparation) will provide a clearer understanding of many issues.

The most studied archeological site is Hueyatlaco (Loc. 102) on the Tetela Peninsula (Fig. 11). Fig. 12 is an attempt at correlation with Bunde's Loc. 103, twenty meters south (cf. Pichardo 2000b). Here a third parameter of comparison is the inclusion of a pedological survey (Cornwall 1971), not undertaken by Malde or Bunde who attended to the alluvial/volcanic sources of Valsequillo deposits. At site X, on the Tetela Road Cornwall identified a Xalnene hard pumice, which corresponds to Bunde's Toluquillo Ash. But at Hueyatlaco (site Y), the clay of levels C and F continued to below water level during Cornwall's visit. The lens here inserted represents stream channel gravel E (Irwin- Williams 1967, 1978) where a semi-articulated horse was found associated with a leaf-shaped Lerma point. Ratio- nale for the correlation derives from the mid- Wisconsin date for Faunal Zone-2 found at, and below, the unconformity in Loc. 103, which is also present at Hueyatlaco. Thus channel E gravels intercalate between Cornwall's dark clay (levels D-F of Irwin- Williams). The hard reddish soil below Cornwall's biotite level over-



Overview of Centrai Mexican Prehistory 165

lies D-F clays and best correlates with Malinche fBo2 soil and the biotite Zone-I fauna of Guenther and Bunde.

Artefact evolutionary sequence

Study of Valsequillo artefacts by Vance Haynes led to the conclusion that the association of an evolutionary sequence of artefacts with extinct fauna throughout a lengthy stratigraphie sequence makes a convincing argument for a greater than 25,000 year age for at least the earlier levels (Haynes 1969; my emphasis). Bifacial stemmed (level-C) and laurel leaf (level-E) points were preceded by unifacial edge- trimmed flake tools (level-I) below the unconformity (Irwin- Williams 1967, Plate 1; 1978, Fig. 3).

Unlike the bifacial Lerma point associated with the horses in level-E, the lower level-I produced an edge- trimmed point on a flake (Irwin- Williams 1967, Plate 6) which later was enhanced by fuming with ammonium chloride to eliminate differences in color (Steen-Mclntyre et al. 1981, Fig. 3). The flat unifacial flake surface is relieved only by the pressure flaking along the edges, and is remarkably similar to a more complete specimen made on flint found imbedded in the mandibular symphy- sis of a mammoth at Arenillas (Armenta 1978, Figs. 9 and 13). The mammoth survived the assault since the point was found in place with renewed bone growth around it. Of interest is that the molar-plate index placed it in Guenther's Mam- muthus imperator category (Guenther 1973, Plate III, 12), and he observed that only at Arenillas was any age segregation found, most being young animals (Guenther 1973, p. 125).

This provocative set of circumstances brings us to focus the urgent need to date Valsequillo sediments. The questions are: 1. Did the M. imperator morphology persist in Central Mexico in relict populations? 2. Was there a later stress-driven evolution of more advanced morphology, or character displacement, which paralleled that of M. jeffersoni of the eastern United States? 3. How much time separates the unifacial tools below the stratigraphie hiatus from the later bifacial tools which recall those of the Great Basin and the Southwestern Plains?

The artefact associations at Tlapacoya have been questioned by proximity to rodent burrows into the brown silt/soil level which directly overlies the alleged hearths. Even these circular areas are problematic since they may be the result of animal rooting (Waters 1985, p. 132). In spite of this criterion, a fact not considered is that all of those specimens accepted as artefacts in the lower levels are unifacial flake tools and, at least provisionally, dated to the mid- Wisconsin Interstadial (Mir- ambell 1986, Garcia-Barcena 1986).

In the overlying calichized soil stratum an obsidian bifacial Lerma point was also found in an old gopher burrow, which was however sealed by overlying stratum (Mirambell 1986, p. 215). Obsidian hydration dates indicate a range from ca. 12,000 - 18,000 yr B.P. (Garcia-Barcena 1986, Fig. 84). This stratum contains a coarse pumice ash which may correspond to the PWA (T2) or to the lower T1 pumice (Garcia-Barcena 1986, Table 6).

Unifacial flake tools are also recorded in several of the mammoth sites around Lake Texcoco (Lorenzo & Mirambell 1986): 1. Sta. Lucia-I, dated 26,000 - 23,900 yr B.P.; 2. Chimalhuacan, undated; 3. Reyes La Paz-I, dated between the UTP and



166 Mario Picharão

the Tl tephra markers; 4. The Texcoco mammoth with obsidian hydration date of 12,600 ± 1,260 yr B.P.; 5. Sta. Lueia-II also obsidian dated at 1 1,170 ± 1,650 yr B.P.

The Iztapan-I mammoth, dated below the PWA marker, contains a bifacial stemmed point but the other five tools are unifacial flakes with edge retouch. Izta- pan-II, below the PWA, produced only bifacial leaf shaped points and a bifacial knife. Thus, evidence from the Texcoco Basin appears to support Haynes' hypothesis of the occurrence of an evolutionary cultural sequence at Valsequillo with unifacial flake tools in lower Hueyatlaco, El Horno, Tecacaxco, Mirador and Caulapan, whereas bifacial tools occur at Hueyatlaco above the unconformity. Uni- facial tools were also collected in the basal gravels of the Upper Becerra at Tequixquiac (Pichardo 1999), and the mid- Wisconsin date for the enclosing deposits in these two valleys accords with the dates for unifacial tools in the lower Tlapacoya level and Sta. Lucia-I in the Lake Texcoco Basin. A possible transitional stage in Haynes' sequence may actually be recorded in the sites listed above dating from between 14,770 - 11,000 yr B.P.

Seven mammoths were buried over frozen soil on the slopes of extinct Tlaloc volcano (Fig. 4) by the great Plinian-type eruption of Popo which the thick PWA (T1 and T2) ash widespread across the Texcoco Basin. Climatic amelioration 3,000 years later permitted lahar formation to bring these deposits downslope to Tocuila (Siebe et al. 1999). As noted by Siebe and Guenther, grazers like mammoths must have ingested great quantities of ash causing dental abrasion and hypoplasia, sub- jecting them to stress from food deprivation. The effects on the megafauna could have triggered an adaptive shift among generalized foragers in this lake habitat who became more selective in searching for food resources. The obviously more pro- ductive hunting of herd-forming large animals like mammoths could have preceded the Clovis manifestation. The Iztapan-I mammoth molar plate index appears to sort with the more specialized M. jeffersoni morphology (Pichardo 2001), and sub- stantiates this interpretation.

Elaborating Haynes' hypothesis can only be schematic at present. Caveats will argue for the late occurrence of flake and blade tools in even post-Pleistocene horizons. The browser Mammut americanum was hunted with a unifacial tool kit at the stratigraphically lower El Horno site, and at lower level-I of Hueyatlaco. But it was also hunted by bifacial tool users at upper level-E where the semi-articulated horse was associated with a Lerma point. This horse has not been identified to species (although possible from its metapodials), but only Equus conversidens and E. francisci were found at level-E in 1966 (Pichardo 2000a, p. 259), whereas the large E. mexicanus occurs in Hueyatlaco level-I below, at Caulapan (lower left premolar, in Nobis 1973, Plate II, 25) and at other sites with Faunal Zone-2 sediments like Arenillas, Zacachimalpa and Hueyatlaco-111 (see Fig. 11 and Bunde 1973 and Nobis 1973).

Problems with the U-series and Fission-track dates in sites along the reservoir caused these important sites to be neglected by American prehistorians. New methods now available, such as ESR dating, offer a solution to these questions and must be pursued (Morían 1988, Pichardo 2000b).




Lake Chapala Basin

Chapala Basin, state of Jalisco, is the westernmost of the Central Mexican Plateau prehistoric areas here discussed. It formed the filling of an east- west trending graben whose northern hanging wall is formed by the Ajijic normal fault (Figs. 3 and 13). The three-toed horse Nannippus indicates late Pliocene sediments are present, but the section ranges to terminal Pleistocene. An incisor of the swamp deer Blastocerus dates to 18,000 yr B.P. (Irish et al. 2000) and fragments of a thick-boned human skull and several projectile point types, including Clovis, have been collected at different locations in still undescribed stratigraphie contexts (Solorzano 1989, 1995, Irish et al. 1998).

Paleontology A typical southern Camelops fauna is present including Camelops , Lamini, Bison pris cus, Tetrameryx , Holmesina , Nothrotheriops , Eremotherium , Equus conversidens and E. mexicanus. Woodland or riverine forms include three species of deer, Neochoerus , Arctodus pristinus (otherwise known only in the eastern U.S.), Pro- cyon , Lutra , Conepatus, Dasypus and the tapir. The three mammoth species identi-

AJIJIC FAULT Â / terraces

I ti soo™ /-^my SANG

30K i 4-¿rny

¡2K 12K f 4 <ynr om ¡2K 12K f 4 <ynr

TWO CREEKS / ' /0^ <ynr

*ISc t ¿ T 3 1 00 m '

li.2-10.7K. / ÒC# CLOVIS

A -^K .E / J Chapala Fm

Nannippus cf. phlegon

Jř ^ Cuvieronius Equus sp.

Platy go nus sp. Crocodilia

Fig. 13. Provisional-preliminary section of north shore Lake Chapala sediments. Lake terrace formation was affected by the Rocky Mountains pluvial regime and not the more complicated Gulf/Atlantic system governing the eastern areas. The underlying Chapala Formation may have produced the three-toed horse Nannippus indicating a Pliocene age for part of Chapala sediments. Most of the fossils however were redeposited into the lake sediments and these are presently under renewed study. Data from Downs (1958), Clements (1963), McDonald (1981) and Solorzano (1989).



168 Mario Pichardo

fied at Valsequillo and the Texcoco Basin are here recorded (Madden 1981). Wolf, coyote and Smilodon fatalis were the major predators. Mammut americanum , present in the Cedazo fauna just to the north (state of Aguascalientes) is absent and instead the tropical Cuvieronius is found (Solorzano 1989, McDonald 1981, Downs 1958).

Fig. 13 shows a generalized stratigraphie section based on Clements (1963) who reported that the lake terraces had not yielded fossils at that time, but may have supplied them to the lake floor deposits exposed during low water stages. Heine (1994, pp. 120-122) points out that late Quaternary Mexican glacial history shows a regional pattern that is not suitable for uncritical correlations with Rocky Mountain pattern which dominated the Southwest. The circum-North Atlantic region's climate was linked to discharge of glacial meltwater and runoff from Lake Agassiz, which alternated either into the North Atlantic or into the Gulf of Mexico through the Mississippi River, between 14,000 - 8,000 yr B.R As a consequence the Younger Dryas glacial advance (12,000 - 10,000 yr B.R) is absent on the flanks of eastern volcanoes like Toluca, Izta, and Malinche because glacial meltwater discharged only into the North Atlantic during this time.

In contrast, the Pleistocene climate of western Mexico appears to resemble that of the southwestern U.S. In the xeric heartland of the Chihuahuan desert, large pluvial lakes and piñon-juniper woodland developed during the late Pleistocene and reflect the influence of the Rocky Mountain climatic system ranging from the Great Basin to Lake Chapala (Bradbury 1982). Consequently, Clements' assignment of the highest Chapala terrace (T-l) to the Illinoian pluvial ca. 0.2 my seems reasonable; some- thing that would not be possible for eastern basins like Texcoco or Valsequillo which responded to the Gulf/ Atlantic system.

Dissection and alluvial fans presumably developed during the succeeding Sanga- mon Interglacial. These deposits were in turn cut by the T-2 terrace during the Wisconsin-I advances ca. 70,000 yr B.P., and mid- Wisconsin Interstadials deposits (30,000 - 21,000 yr B.P.) overlie them. T-3 terrace would represent the LGM, Wisconsin-II advance, which in turn was overlaid by the Two Creek Interstadials sediments, ca. 12,000 yr B.P.

This very preliminary schematic is only an orientation to offer students a broad general morphostratigraphy. Equally, preliminary studies by Solorzano, Irish and their associates are now being directed to a broader spatial and temporal program of research.

Conclusion

An overview of Central Mexican prehistory is long overdue. The half century of neglect for what may be considered the cross-roads of Paleoindian population movements must be replaced by renewed field work to enhance and resolve the implications of recent work discussed above. Of special importance must be the develop- ment of a controlled tephrachronology for the Lake Texcoco Basin mammoth locations, which should be done in concert with the measurement and plotting of all molar specimens in order to assign preliminary species groups. Mammoth taxonomy in Central Mexico can be resolved by locating the three morphs within the tephra




sequence. It may be that there really was a 'character displacement' which produced late populations which paralleled the apomorphic dental traits of Mammuthus jeffersoni of eastern U.S. locations. In such a case the Mexican forms may be only a subspecies of M. columbi (M. c. felicis , Fig. 8). A controlled tephra sequence will also permit a formal definition of the Becerra Formation at the stratotype section and allow its correlation with the classic Tequixquiac sequence.

Dating of the topographically lower Valsequillo sites must be implemented by use of ESR, Electron-Spin Resonance, to finally clarify the confusion of erratic dates from U-series and Fission-track methods. ESR dating should also be applied to settle the uncertainty regarding the possible burial of the human fossil from Tepexpan, and perhaps on the newly found remains from Lake Chapala.

There is work for many years to come which cannot be accomplished by any single individual or institution. Students from Mexico, the U.S., Canada, Germany, France, and any others interested, are encouraged to enter this field.

References

Alvarez, T. (1965): Catalogo paleomastozoologico Mexicano. - INAH, Mexico, Dept. Pre- historia 17, 1-70.

- (1986): Fauna Pleistocenica. - In: Lorenzo, J. & Mirambell, L. (eds.): Tlapacoya: 35,000 años de historia del Lago de Chalco. - Serie prehist. INAH 115, 173-203.

Anderson, D. & Gillam, C. (2000): Paleoindian colonization of the Americas: Implications from an examination of physiography, demography, and artifact distribution. - Amer. Antiq. 65, 43-66.

Arellano, A. (1946): Datos geologicos sobre la antigüedad del hombre en la Cuenca de Mexico. - Mem. 2nd Congr. Mex. Cienc. Soc 5, 213-219.

- (1951): The Becerra Formation (latest Pleistocene) of Central Mexico. - Int. Geol. Congr., Rept. of 18th Session, 1948, XI, 55-62.

- (1953): Estratigrafia de la Cuenca de Mexico. - Mem. Congr. Cienc. Mex. 3, 172-186. Armenta, J. (1978): Vestigios de labor humana en huescos de animales extintos de Valsequillo,

Puebla, Mexico. - Consejo Edit, del Gob. del Estado de Puebla, Mexico, 1-128. Azzaroli, A. (1998): The genus Equus in North America - the Pleistocene species. - Palaeon-

tographica Italica 85, 1-60. Barbour, C. (1973): A biogeographical history of Chirostoma (Pisces: Atherinidae): a species

flock from the Mexican Plateau. - Copeia 3, 533-556. Birdsell, J. (1951): The problem of the early peopling of the Americas as viewed from Asia. -

In: Laughlin, W. (ed.): Papers on the physical anthropology of the American Indian. - Viking Fund, New York, pp. 1-68.

Bradbury, J. (1982): Holocene chronostratigraphy of Mexico and Central America. - In: Mangerud, J., Birks, H. & Jager, K. (eds.): Chronostratigraphic subdivision of the Holo- cene. - Striae 16, 46-48.

Bridgland, D. (2000): River terrace systems in north-west Europe: an archive of environmental change, uplift and early human occupation. - Quarter. Sci. Rev. 19, 1293-1303.

Bryan, A. (1978): An overview of Paleo- American prehistory from a circum-Pacific perspective. - In: Bryan, A. (ed.): Early Man in America from a circum-pacific perspective. - Archeol. Res. Intl., Edmonton, pp. 306-327.

Bryan, K. (1946): Comentario e intento de correlación con la cronologia glacial. - Mem. 2nd Cong.. Mex. Cienc. Soc. 5, 220-225.

- (1948): Los suelos complejos y fósiles de la Cuenca de Mexico en relación a los cam- bios climáticos. - Bol. Soc. Geol. Mex. 13, 1-20.



170 Mario Pichardo

Bunde, H. (1973): Geologische Untersuchungen im Gebiet des Valsequillo südlich von Puebla, Mexiko. - In: Das Mexiko-Projekt der Deutschen Forschungsgemeinschaft VI. - Franz Steiner Verlag, Wiesbaden, pp. 21-93.

Caballero, M. & Ortega-Guerrero, B. (1998): Lake levels since about 40,000 years ago at Lake Chalco, near Mexico City. - Quatern. Res. 50, 69-79.

Cabral-Perdomo, M. & Castillo-Ceron, J. (1997): Pleistocene mammals from the Valsequillo Basin, Central Mexico. - J. Vertebr. Paleontol. Abstract 17, 35A.

Carlson, R. (1983): The Far West. - In: Shutler, R. (ed.): Early Man in the New World. - Sage Pubis. California, pp. 73-96.

Carr, S. & Hughes, G. (1993): Direction of introgressive hybridization between species of North American deer ( Odocoileus ) as inferred from mitochondrial cytochrome-b se- quences. - J. Mammal. 74, 33 1-342.

Carrara, P. (1995): A 12,000 year radiocarbon date of déglaciation from the Continental Divide of northwestern Montana - Can. J. Earth Sci. 32, 1303-1307.

Clements, T. (1963): Pleistocene history of Lake Chapala, Jalisco, Mexico. - University of South California, Los Angeles.

Cornwall, I. (1971): Geology and Early Man in Central Mexico. - Proc. Geol. Assoc. (London 1970). -82, 379-391.

del Castillo, A. (1869): Classificacion y datos sobre los mamíferos encontrados en el Valle de Mexico. (Translation into German by J. Burkart). - Z. Dt. Geol. Ges. 21, 479-482.

DeTerra, H. (1959): A successor of Tepexpan man in the Valley of Mexico. - Science 129, 563-564.

DeTerra, H., Romero, J. & Stewart, T. (1949): Tepexcan Man. -Viking Fund No. 11, New York.

Doutt, J. & Black, C. (1962): A new Pleistocene locality in the state of Oaxaco, Mexico. - J. Mammal. 43, 414-415.

Downs, T. (1958): Fossil vertebrates from Lago de Chapala, Jalisco. - 20th Intl. Geol. Congr. Mexico (1956), 7, 75-77.

Felix, J. & Lenk, A. (1889): Beiträge zur Geologie und Paläontologie der Republik Mexiko. Teil. I. - Leipzig.

Flores-Diaz, A. (1986): Fluctuaciones del Lago de Chalco, desde hace 35 mil años al presente. - In: Lorenzo, J. & Mirambell, L. (eds.): Tlapacoya: 35,000 años de historia del Lago de Chalco. - Serie prehist. INAH 115, 109-156.

Garcia-Barcena, J. (1986): Algunos aspectos cronologicos. - In: Lorenzo, J. & Mirambell, L.(eds.): Tlapacoya: 35,000 años de historia del Lago de Chalco. - Serie prehist. INAH 115, 219-224.

Goebel, T., Derevianko, A. & Petrin, V. (1993): Dating the Middle-to-Upper Paleolithic transition at Kara-Bom. - Current Anthropology 14, 452-458.

Graham, R. et al. (1996): Spatial response of mammals to late Quaternary environmental fluctuations. - Science 272, 1601-1606.

Gruhn, R. (1988): Linguistic evidence in support of the coastal route of earliest entry into the New World. - Man 23, 77-100.

- (1992): Some caveats regarding linguistic diversity and the peopling of the Americas. - Man 27, 406-407.

Guenther, E.W. (1973): Elefantenzähne aus dem Valsequillo südlich von Puebla (Mexiko). - In: Das Mexiko-Projekt der Deutschen Forschungsgemeinschaft VI. - Franz Steiner Ver- lag, Wiesbaden, pp. 109-177.

Harington, C. (1980): Radiocarbon dates on some Quaternary mammals from northern North America. - Arctic 33, 815-832.

Harington, C. & Clulow, F. (1973): Pleistocene mammals from Gold Run Creek, Yukon Territory. - Can. J. Earth Sci. 10, 697-759.

Hay, O. (1925): Extinct proboscideans of Mexico. - Pan-American Geologist 44, 21-37. Haynes, V. (1969): Comments of 'Bryan: Early Man in America'. - Current Anthropology 10,

353-354.




Haynes, V. (1976): Mammoth hunters of the USA and USSR. - In: 'Beringian Cenozoic' (no eds.). - Far Eastern Acad. Sci., Vladivostok, pp. 557-570.

Heine, K. (1978): Neue Beobachtungen zur Chronostratigraphie der mittelwisconsinzeit- lichen Vergletscherungen und Böden mexikanischer Vulkane. - Eiszeitalter u. Gegenwart 28, 139-147.

- (1984): The classical late Weichselian climatic fluctuations in Mexico. - In: Morner, N. & Karlen, W. (eds.): Climatic changes on a yearly to millennial basis. - Reidel, Dor- drecht, pp. 95-115. - (1994): The late-glacial moraine sequence in Mexico: is there evidence for the Younger Dryas? - Palaeogeography, Palaeoclimatalogy, Palaeoecology 112, 113-123.

- (1998): Geomorphologische Beobachtungen zur Besiedelungsgeschichte der Neuen Welt: Das Problem des 'eisfreien Korridors'. - Regensburger Beiträge zur Prähist. Archäologie 5, 1-22.

Herrera, A. (1893): El hombre prehistórico de Mexico. - Mem. Rev. Cient. Antonio Alzate 7, 17-56.

Hibbard, C. (1955): Pleistocene vertebrates from the Upper Becerra (Becerra Superior) For- mation, Valley of Tequixquiac, Mexico, with notes on other Pleistocene forms.- Contrib. Mus. Paleont. Univ. Michigan 12, 47-96.

Holliday, V. & Meitzer, D. (1996): Geoarchaeology of the Midland (Paleoindian) site, Texas. - Amer. Antiq. 61, 755-771.

Irish, J., Lobdell, J., Davis, S. & Solorzano, F. (1998): Potential early prehistoric human remains from Jalisco, Mexico: A revised assessment. - Amer. Assoc. Phys. Anthrop. Abstracts 26, 126.

Irish, J., Davis, S., Lobdell, J. & Solorzano, F. (2000): Prehistoric human skeletal remains from Jalisco, Mexico. - Curr. Res. Pleist. 17, 95-97.

Irwin- Williams, C. (1967): Association of Early Man with horse, camel and mastodon at Hueyatlaco, Valsequillo. - In: Martin, P. & Wright, H. (eds): Pleistocene extinctions: the search for a cause. - Yale University Press, New York, pp. 337-347. - (1978): Summary of archaeological evidence from the Valsequillo region, Puebla, Mex- ico. - In: Browman, D. (ed.): Cultural continuity in Mesoamerica. - Aldine, Chicago, pp. 7-22.

Irwin- Williams, C. & Haynes, V. (1970): Climatic change and early population dynamics in the southwestern United States. - Quatern. Res. 1, 59-71.

Kurten, B. & Anderson, E. (1980): Pleistocene mammals of North America. - Columbia University Press, New York.

Lambert, W. (1986): Descripción preliminar de los estratos de tefra en Tlapacoya I. - In: Lorenzo, J. & Mirambell, L. (eds.): Tlapacoya: 35,000 años de historia en el Lago de Chalco. - Serie prehist. INAH 115, 77-100.

Libby, W. (1955): Radio Carbon dating. 2nd edition. - University of Chicago Press, Chicago. Lorenzo, J. & Mirambell, L. (1986): Mamutes excavados en la Cuenca de Mexico (1952-

1980). - Dept. Prehist., INAH, Cuaderno Trabajo 32, 1-151. Lozano-Garcia, M., Ortega-Guerrero, B., Caballero-Miranda, M. & Urrutia-Fucugauchi, J.

(1993): Late Pleistocene and Holocene Paleo-environments of Chalco Lake, Central Mex- ico. - Quatern. Res. 40, 332-343.

Lundelius, E. (1972): Fossil vertebrates from the late Pleistocene Ingleside fauna, San Patricio Co., Texas. - Bureau Econ. Geol. Rept. Investig. 77, 1-74.

Lynch, T. (1990): Glacial- Age Man in South America? A critical Review. - Amer Antiq H' 55 12-36. H' '

Madden, C. (1981): Mammoths of North America. - Unpublished PhD Thesis, University of Colorado, Boulder.

Malde, H. (1978): La Malinche series, Mexico. - Radiocarbon 20, 299-303. Martin, P. (1973): The discovery of America. - Science 179, 969-974. McDonald, J. (1981): North America bison: their classification and evolution. - University of

California Press, Berkeley.



172 Mario Pichardo

McDonald, J. (1984): The reordered North American selection regime and late Quaternary megafauna extinctions. - In: Martin, P. & Klein, R. (eds.): Quaternary extinctions: a prehistoric revolution. - University of Arizona Press, Tucson, pp. 404-439.

Meitzer, D. (1995): Clocking the first Americans. - Ann. Rev. Anthrop. 24, 21-45. Meitzer, D., Grayson, D., Ardila, G., Barker, A., Dincauze, D., Haynes, V., Mena, P., Nuñez,

L. & Stanford, D. (1997): On the Pleistocene antiquity of Monte Verde, southern Chile. - Amer. Antiq. 62, 659-663.

Mickelson, D., Clayton, L., Fullerton, D. & Borns, H. (1983): The late Wisconsin glacial record of the Laurentide ice sheet in the United States. - In: Wright, H. (ed.): Late Quaternary environments of the United States; Porter, S. (ed.): The Late Pleistocene 1. - University of Minnesota Press, Minneapolis, pp. 3-37.

Miller, W. & Carranza-Castañeda, O. (1984): Late Cenozoic mammals from Central Mexico. - J. Verteb. Paleont. 4, 216-236.

Mirambell, L. (1986): Las excavaciones. - In: Lorenzo, J. & Mirambell, L. (eds.): Tlapacoya: 35,000 años de historia del Lago de Chalco. - Serie prehist. INAH 115, 13-56.

Montellano, M. (1989): Late Cenozoic mammal faunas from Aguascalientes, Mexico. - J. Verteb. Paleontol. Abstracts 9, 3 3 A.

Mooser, F. (1963): La Cuenca lacustre del Valle de Mexico. - In: Mesas Redondas sobre problemas del Valle de Mexico (no eds.). - Recursos Nat. Renov. A.C., Mexico, pp. 1-48. - (1967): Tefracronologia de la Cuenca de Mexico para los últimos treinta mil años. - INAH Boletín 30, 12-15.

- (1990): Estratigrafia y estructura del Valle de Mexico. - In: Ovando, F. & Gonzalez, F. (eds.): El subsuelo de la Cuenca de Mexico en relación con la ingeniería. - Soc. Méx. de Mecanica de Suelos, pp. 29-36.

Mooser, F. & Rul, F. (1961): Erupciones volcánicas y el hombre primitivo en la Cuenca de Mexico. - In: Homenaje a Palbo Martinez del Rio (no eds.). - INAH, Mexico, pp. 137-141 .

Mooser, O. & Dalquest, W. (1975): Pleistocene mammals from Aguascalientes, Central Mexico. - J. Mammal. 56, 781-820.

Morett, L., Arroyo-Cabrales, J. & Polaco, O. (1998): Tocuila, a remarkable mammoth site in the Basin of Mexico. - Curr. Res. Pleist. 15, 118-120.

Morían, R. (1988): Pre-Clovic people: early discoveries of America? - Ethnol. Monogr. 12, 31-43.

Müller-Beck, H. (1966): Paleohunters in America: Origins and diffusion. - Science 152, 1191-1210.

Neumann, G. (1952): Archaeology and Race in the American Indians. - In: Griffin, J. (ed.): Archaeology of the eastern United States. - University of Chicago Press, Chicago, pp. 13- 34.

Newman, M. (1953): The application of ecological rules to the racial anthropology of the aboriginal New World. - Amer. Anthropol. 55, 311-327.

Nichols, J. (1990): Linguistic diversity and the first settlement of the New World. - Language 66, 475-521.

Nobis, G. (1973): Die Equidenreste aus dem Pleistozän des Valsequillo (Mexiko). - In: Das Mexiko-Projekt der Deutschen Forschungsgemeinschaft VI. - Franz Steiner Verlag, Wies- baden, pp. 95-108.

Ortega-Guerrero, B. & Newton, A. (1998): Geochemical characteristics of late Pleistocene and Holocene tephra layers from the Basin of Mexico, Central Mexico. - Quatern. Res. 50 90-106.

Pichardo, M. (1997): Valsequillo Biostratigraphy: New evidence for a Pre-Clovis date. - Anthrop. Anz. 55, 233-246. - (1998): Amerind Taxonomy and testable hypotheses. - Anthrop. Anz. 56, 97-116. - (1999): Valsequilo Biostratigraphy II. Bison, Tools, Correlate with Tequixquiac. - Anthrop. Anz. 57, 13-24. - (2000a): Valsequillo Biostratigraphy III: Equid ecospecies in Paleoindian sites - Anthrop. Anz. 58, 275-298.




Pichardo, M. (2000b): Redating Iztapan and Valsequillo Mexico. - Radiocarbon 42, 305-310. - (2001): Valsequillo Biostratigraphy IV: Proboscidean ecospecies in Paleoindian sites. -

Anthrop. Anz. 59, 41-60. - (2004): Review of horse species in Paleoindian sites of the Americas. - Anthrop. Anz.,

in press. Pichardo, M., Bonilla, J. & Hoppe, W. (1961): El mammut posiblemente mas antiguo de la

Cuenca de Mexico. - In: Homenaje a Pablo Martinez del Rio (no eds). - INAH, Mexico, pp. 113-124.

Rogers, R., Martin, L. & Nicklas, D. (1990): Ice-age geography and the distribution of native North American languages. - J. Biogeogr. 17, 131-143.

Roosevelt, T. et al. (1996): Paleoindian cave dwellers in the Amazon: the peopling of the Americas. - Science 272, 373-384.

Siebe, C., Abrams, M. & Macias, J. (1995): Derrumbes gigantes, depósitos de avalancha de escombros y edad del actual cono del volcan Popocatepetl. - CENAPRED-UNAM, Mex- ico, pp. 195-230.

Siebe, C., Schaaf, P. & Urrutia-Fueugauchi, J. (1999): Mammoth bones embedded in a late Pleistocene lahar from Popocatepetl volcano, near Tocuila, Central Mexico. - GSA Bull. Ill, 1550-1562.

Silva-Barcenas, A. (1969): Localidades de vertebrados fósiles en la Republica Mexicana. - UNAM, Inst. Geol. 28, 1-34.

- (1987): El material de Proboscidea alojado en el Museo del Instituto de Geologia: una evaluación. - Rev. Soc. Méx. Paleontol. 1, 300-312.

Soffer, O. (1989): The Middle to Upper Palaeolithic transition on the Russian Plain. - In: Mellars, P. & Stringer, C. (eds.): The Human Revolution. - Edinburgh University Press, Edinburgh, pp. 714-741.

Solorzano, F. (1989): Pleistocene artifacts from Jalisco, Mexico: A comparison with some pre-Hispanic artifacts. - In: Bonnichsen, R. & Sorg, M. (eds.): Bone modification. - Ctr. Study First Americans, University of Maine, Orono, pp. 499-514. - (1995): Hallazgo de un fossil humano con características notoriamente primitivas que plantea interragaciones difíciles de contestar. - Rev. Soc. Méx. Paleontol. 8, 87-105.

Soto-Heim, P. (1994): Les hommes de Lagoa Santa (Brésil). Caracteres anthropologiques et position parmi d'autres populations Paleoindiennes d'Amerique. - L'Anthropologie 98, 81-109.

Steele, D. & Powell, J. (1992): Peopling of the Americas; paleobiological evidence. - Hum. Biol. 64, 303-336.

Steen-Mclntyre, V., Fryxell, R. & Malde, H. (1981): Geologic evidence for age of deposits at Hueyatlaco archaeological site, Valsequillo, Mexico. - Quatern. Res. 16, 1-17.

Tamayo, J. & West, R. (1964): The hydrography of Middle America. - In: Handbook of Middle American Indians I. - University of Texas Press, Austin, pp. 84-121.

Taylor, R. (2000): The contribution of radiocarbon dating to New World archaeology. - Radiocarbon 42, 1-21.

Vasil'ev, S. (1993): The Upper Palaeolithic of Northern Asia. - Current Anthropology 14, 82- 92.

Villada, M. (1903): Apuntes de la fauna fósil del Valle de Mexico. - Anal. Mus. Nac. Mexico 7, 441-451.

Waters, M. (1985): Early Man in the New World: an evaluation of the radiocarbon dated pre- Clovis sites in the Americas. - In: Mead, J. & Meitzer, D. (eds.): Environments and extinctions: Man in late glacial North America. - University of Maine, Orono, pp. 1 25- 143.

West, R. (1964): Surface configuration and associated geology of Middle America. - In: Handbook of Middle American Indians I. - University of Texas Press, Austin, pp. 33-83.

Wilson, M. (1996): Late Quaternary vertebrates and the opening of the Ice-free Corridor, with special reference to the genus Bison. - Quatern. Intl. 32, 97-105.



174 Mario Picharão

Wormington, M. (1957): Ancient Man in North America. ~ Denver Mus. Nat. Hist., Popular ser. No. 4.

Received May 27, 2002

Address for correspondence: Dr. Mario Pichardo, 27 14th St., W., Minneapolis, MN, 55403, USA



Documents

Overview of Central Mexican Prehistory: Morphostratigraphy, Chronostratigraphy, Biostratigraphy