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The human settlement of the Americas has been a topic of intense debate for centuries, and there is still no consensus on the tempo and mode of early human dispersion across the continent. When trying to explain the biological diversity of early groups across North, Central and South America, studies have defended a wide range of dispersion models that tend to oversimplify the diversity observed across the continent. In this study, we aim to contribute to this debate by exploring the cranial morphological affinities of four late Pleistocene/early Holocene specimens recovered from the caves of Quintana Roo, Mexico. The four specimens are among the earliest human remains known in the continent and permit the contextualization of biological diversity present during the initial millennia of human presence in the Americas. The specimens were compared to worldwide reference series through geometric morphometric analyses of 3D anatomical landmarks. Morphological data were analyzed through exploratory visual multivariate analyses and multivariate classification based on Mahalanobis distances. The results show very different patterns of morphological association for each Quintana Roo specimen, suggesting that the early populations of the region already shared a high degree of morphological diversity. This contrasts with previous studies of South American remains and opens the possibility that the initial populations of North America already had a high level of morphological diversity, which was reduced as populations dispersed into the southern continent. As such, the study of these rare remains illustrates that we are probably still underestimating the biological diversity of early Americans.

Preceramic human skeletal remains preserved in submerged caves near Tulum in the Mexican state of Quintana Roo, Mexico, reveal conflicting results regarding 14C dating. Here we use U-series techniques for dating a stalagmite overgrowing the pelvis of a human skeleton discovered in the submerged Chan Hol cave. The oldest closed system U/Th age comes from around 21 mm above the pelvis defining the terminus ante quem for the pelvis to 11311±370 y BP. However, the skeleton might be considerable older, probably as old as 13 ky BP as indicated by the speleothem stable isotope data. The Chan Hol individual confirms a late Pleistocene settling of Mesoamerica and represents one of the oldest human osteological remains in America.

Key evidence of human occupation in Africa during the Middle Palaeolithic (Middle Stone Age [MSA]) is available from the south and east of the continent, where semi-arid climate prevails. Rare evidence of MSA human occupation in the humid tropical region was recently reported from Equatorial Guinea. To identify if paleolithic human occupation occurred in the tropical forest, the stratigraphy of the recently discovered archaeological site “Mabewele I” was analyzed using a paleopedological approach. The properties evaluated along a vertical profile are: granulometry, magnetic susceptibility (K), free iron extractable with sodium dithionite (Fed), total organic carbon (TOC), chemical composition by X-ray fluorescence (XRF), X-ray diffraction mineralogy (XRD), ternary plot of the three main oxides (SiO2-Al2O3-Fe2O3), phytoliths and micromorphology. The predominant fraction is sand, with a significant clay content (> 30 %). The K and the Fed presented low values, as well as the TOC. XRF showed few variations along the sequence and XRD showed that the clays are mainly kaolinites, with a very low component of vermiculites. The phytoliths correspond to tropical vegetation with few changes in the vegetal composition between the deep and superficial zones. A charcoal from the lower part of the profile was dated between 12.57-12.24 ka cal BP, while the main artifact horizon was located at the bottom. The analytical results appear contradictory: on the one hand, there is evidence of intense chemical weathering under a humid tropical climate, but the clay cutans in the pores are very scarce and incipient and the iron nodules are mostly anorthic. This indicates that the sequence is composed of pedosediments associated with a high environmental dynamism, with short periods of erosion-sedimentation-pedogenesis. The results allow us to propose that humans inhabited the tropical forest during the MSA and that erosion-sedimentation processes could be related to anthropization processes.

Key evidence of human occupation in Africa during the Middle Palaeolithic (Middle Stone Age [MSA]) is available from the south and east of the continent, where semi-arid climate prevails. Rare evidence of MSA human occupation in the humid tropical region was recently reported from Equatorial Guinea. To identify if paleolithic human occupation occurred in the tropical forest, the stratigraphy of the recently discovered archaeological site “Mabewele I” was analyzed using a paleopedological approach. The properties evaluated along a vertical profile are: granulometry, magnetic susceptibility (K), free iron extractable with sodium dithionite (Fed), total organic carbon (TOC), chemical composition by X-ray fluorescence (XRF), X-ray diffraction mineralogy (XRD), ternary plot of the three main oxides (SiO₂-Al₂O₃-Fe₂O₃), phytoliths and micromorphology. The predominant fraction is sand, with a significant clay content (> 30 %). The K and the Fed presented low values, as well as the TOC. XRF showed few variations along the sequence and XRD showed that the clays are mainly kaolinites, with a very low component of vermiculites. The phytoliths correspond to tropical vegetation with few changes in the vegetal composition between the deep and superficial zones. A charcoal from the lower part of the profile was dated between 12.57-12.24 ka cal BP, while the main artifact horizon was located at the bottom. The analytical results appear contradictory: on the one hand, there is evidence of intense chemical weathering under a humid tropical climate, but the clay cutans in the pores are very scarce and incipient and the iron nodules are mostly anorthic. This indicates that the sequence is composed of pedosediments associated with a high environmental dynamism, with short periods of erosion-sedimentation-pedogenesis. The results allow us to propose that humans inhabited the tropical forest during the MSA and that erosion-sedimentation processes could be related to anthropization processes. Las principales evidencias de ocupación humana en África durante la Edad de la Piedra Media (Middle Stone Age —MSA-) se han hallado en el sur y el este del continente, en las regiones de climas secos. Sin embargo, investigaciones recientes en la región tropical de Guinea Ecuatorial han hallado artefactos arqueológicos de dicho periodo. Para identificar si la ocupación humana paleolítica ocurrió en la selva tropical, se analizó la estratigrafía del sitio arqueológico “Mabewele I”, recientemente descubierto, bajo un enfoque paleopedológico. Las propiedades evaluadas fueron: granulometría, susceptibilidad magnética, hierro libre extractable con ditionito de sodio (Fed), carbono orgánico total (TOC), composición química por Fluorescencia de rayos X (FRX), mine­ralogía por difracción de rayos X (DRX), fitolitos y micromorfología. La fracción predominante es la arena, con un contenido de arcillas importante. La K y el Fed presentaron valores bajos, al igual que el TOC. La FRX mostró pocas variaciones a lo largo de la secuencia y la DRX indicó que las arcillas son principalmente caolinitas, con un componente muy bajo de vermiculitas. Los fitolitos corresponden a vegetación tropical, con pocos cambios en la composición vegetal entre las zonas profunda y superficial. Un carbón de la parte baja del perfil fue datado entre 12.57-12.24 ka Cal AP, mientras que los artefactos fueron localizados al fondo. Los resultados analíticos son contradictorios: por un lado, hay evidencias de intemperismo químico intenso bajo un clima tropical húmedo, pero los cutanes de arcilla en los poros son muy escasos e incipientes y los nódulos de hierro son mayormente anórticos. Ello indica que la secuencia se compone de pedosedimentos asociados a un alto dinamismo ambiental, con cortos periodos de erosión-sedimentación-pedogénesis. Los resultados permiten proponer que los humanos habitaron la selva tropical durante el MSA y que los procesos de erosión-sedimentación podrían estar relacionados con procesos de antropización.

Alonso, Antonio, Pablo Martín, Cristina Albarrán, Pilar García, Dragan Primorac, Oscar García, Lourdes Fernánd ez de Simón, Julia García-Hirschfeld, Man uel San cho y José Fernánd ez-Piqueras 2003 Specific Quantification of Human Genomes from Low Copy Number dna Samples in Forensic and Ancient dna Studies, Croatian Medical Journal 44 (3): 273-280. Armitage, Mark 2001 [en línea] Scanning Electron Microscope study of mummified collagen fibers in fossil tyrannosaurus rex bone, Creation Research Society Quarterly Journal 38 (2): 61-66, [consulta: 29 de noviembre del 2009]. H olland , Mitchell, Deborah Fisher, Mitchell Lloyd, William Rodríquez, Jam es Can ik, Carl Merril y Victor Weedn 1993 Mitochondrial dna sequence analysis of human skeletal remains: identification of remains from the Vietnam war, Journal of Forensic Sciences 38 (3): 542-553. S m ith, Colin, And rew Cham berlain, Michael Riley, Chris Stringer y Ma-tthew Collins 2003 [en línea] The thermal history of human fossils and the likelihood of successful DNA amplification, Journal of Human Evolution, 45: 203-217, [consulta: 18 de abril de 2010].