Marina Laura Sardi

Craniometric evidence for Palaeoamerican survival in Baja California

A current issue on the settlement of the Americas refers to the lack of morphological affinities between early Holocene human remains (Palaeoamericans) and modern Amerindian groups, as well as the degree of contribution of the former to the gene pool of the latter. A different origin for Palaeoamericans and Amerindians is invoked to explain such a phenomenon. Under this hypothesis, the origin of Palaeoamericans must be traced back to a common ancestor for Palaeoamericans and Australians, which departed from somewhere in southern Asia and arrived in the Australian continent and the Americas around 40,000 and 12,000 years before present, respectively. Most modern Amerindians are believed to be part of a second, morphologically differentiated migration. Here we present evidence of a modern Amerindian group from the Baja California Peninsula in Mexico, showing clearer affinities with Palaeoamerican remains than with modern Amerindians. Climatic changes during the Middle Holocene probably generated the conditions for isolation from the continent, restricting the gene flow of the original group with northern populations, which resulted in the temporal continuity of the Palaeoamerican morphological pattern to the present.

Discrepancy between cranial and DNA data of early Americans: implications for American peopling.

Currently, one of the major debates about the American peopling focuses on the number of populations that originated the biological diversity found in the continent during the Holocene. The studies of craniometric variation in American human remains dating from that period have shown morphological differences between the earliest settlers of the continent and some of the later Amerindian populations. This led some investigators to suggest that these groups—known as Paleomericans and Amerindians respectively—may have arisen from two biologically different populations. On the other hand, most DNA studies performed over extant and ancient populations suggest a single migration of a population from Northeast Asia. Comparing craniometric and mtDNA data of diachronic samples from East Central Argentina dated from 8,000 to 400 years BP, we show here that even when the oldest individuals display traits attributable to Paleoamerican crania, they present the same mtDNA haplogroups as later populations with Amerindian morphology. A possible explanation for these results could be that the craniofacial differentiation was a local phenomenon resulting from random (i.e. genetic drift) and non-random factors (e.g. selection and plasticity). Local processes of morphological differentiation in America are a probable scenario if we take into consideration the rapid peopling and the great ecological diversity of this continent; nevertheless we will discuss alternative explanations as well.

Early peopling and evolutionary diversification in America

Abstract Several cranial-functional studies were made to compare the major (neurocranium and face) and minor (anteroneural, midneural, posteroneural, otic, optic, respiratory, masticatory, and alveolar) cranial components in different human populations. In the present study, samples from Paleoamericans and ancient and modern Amerindians from Valley of Mexico, Lagoa Santa, Tierra del Fuego Island, and Minas Gerais (Botocudos) were compared. The aim was to test the hypotheses that (1) “There are non-significant differences in the functional cranial components of different Paleoamerican crania, since they proceeded from a single dispersive effect” and that (2) “The biological variability of Paleoamerican and Amerindian functional cranial components was produced by random diversification evoked—after migration—by stochastic evolution”. Its acceptance will hold the criterion of temporal discontinuity between “megapopulations”, with a high incidence of migration and genetic drift. Its rejection will mean that Paleoamericans were not a morphologically homogeneous substratum, and that further populations could have—at least in part—originated from one or several central nuclei highly diversified by non-stochastic processes, like selection and adaptation. Multivariate (discriminant analysis and hierarchical clusters) were employed to get a general sample distribution. Univariate between-group standardized sD 2 distances were calculated to measure absolute and relative within-component differences. Statistical analyses were performed by the SYSTAT 9 program. Results lead us to reject both null hypotheses, suggesting that: (1) some cranial-functional differences were evident between both Paleoamerican samples, and (2) that several adaptative trends from Paleoamericans to modern Amerindians, and between Amerindians, might have occurred. It was concluded that adaptation could explain a fraction of the non-detectable cranial variation by the non-functional craniometric methods not explained by the “migration-drift” model for the American diversification.

Spatial patterns and evolutionary processes in southern South America: A study of dental morphometric variation

The purpose of this article is to examine the patterns of evolutionary relationships between human populations from the later Late Holocene (1,500-100 years BP) of southern South America on the basis of dental morphometric data. We tested the hypotheses that the variation observed in this region would be explained by the existence of populations with different phylogenetic origin or differential action of gene flow and genetic drift. In this study, we analyzed permanent teeth from 17 samples of male and female adult individuals from throughout southern South America. We measured mesiodistal and buccolingual diameters at the base of the crown, along the cement-enamel junction. The results of multiple regression analysis and a mantel correlogram indicate the existence of spatial structure in dental shape variation, as the D(2) Mahalanobis distance between samples increases with increasing geographical distance between them. In addition, the correlation test results show a trend toward reduction of the internal variation of samples with increasing latitude. The detected pattern of dental variation agrees with the one expected as an outcome of founder serial effects related to an expansion of range during the initial occupation of southern South America.

Allometries Throughout the Late Prenatal and Early Postnatal Human Craniofacial Ontogeny

Craniofacial shape changes throughout the late prenatal and early postnatal ontogeny (32–47 weeks of gestational age) were explored. The purpose was to evaluate whether the skull follows an allometric growth pattern, as was observed in other ontogenetic periods, and to assess shape variation patterns for the cranial vault, cranial base, and face. Thirty three‐dimensional landmarks were registered in 54 skulls. Wire‐frames were built with landmarks to observe shape variation in the following cranial components: anteroneural, midneural, posteroneural, optic, respiratory, masticatory, and alveolar. The landmark configurations were subjected to generalized Procrustes analyses, and the shape coordinates obtained were subjected to Principal Components Analyses. Multivariate regression of the shape variables (the principal components) on the size vector (the centroid size) was performed to assess allometries. Transformation grids were constructed to identify how cranial components interact across ontogeny. Results indicated that highly significant shape changes depend on size changes. Important shape variation in the vault, small variation in the cranial base, and no variation in the face were observed. Brain growth is proposed to be the major influence on craniofacial shape change, which produces a relative elongation and compression of midneural and posteroneural components. The cranial base elongates by intrinsic factors and affects position of the face. Ontogenetically, the cranial base seems to be independent with respect to brain growth, in contrast to what has been suggested in comparisons at higher taxonomic levels. Anat Rec, 290:1112–1120, 2007.

Different Cranial Ontogeny in Europeans and Southern Africans

Modern human populations differ in developmental processes and in several phenotypic traits. However, the link between ontogenetic variation and human diversification has not been frequently addressed. Here, we analysed craniofacial ontogenies by means of geometric-morphometrics of Europeans and Southern Africans, according to dental and chronological ages. Results suggest that different adult cranial morphologies between Southern Africans and Europeans arise by a combination of processes that involve traits modified during the prenatal life and others that diverge during early postnatal ontogeny. Main craniofacial changes indicate that Europeans differ from Southern Africans by increasing facial developmental rates and extending the attainment of adult size and shape. Since other studies have suggested that native subsaharan populations attain adulthood earlier than Europeans, it is probable that facial ontogeny is linked with other developmental mechanisms that control the timing of maturation in other variables. Southern Africans appear as retaining young features in adulthood. Facial ontogeny in Europeans produces taller and narrower noses, which seems as an adaptation to colder environments. The lack of these morphological traits in Neanderthals, who lived in cold environments, seems a paradox, but it is probably the consequence of a warm-adapted faces together with precocious maturation. When modern Homo sapiens migrated into Asia and Europe, colder environments might establish pressures that constrained facial growth and development in order to depart from the warm-adapted morphology. Our results provide some answers about how cranial growth and development occur in two human populations and when developmental shifts take place providing a better adaptation to environmental constraints.

Diversity among African Pygmies

Although dissimilarities in cranial and post-cranial morphology among African pygmies groups have been recognized, comparative studies on skull morphology usually pull all pygmies together assuming that morphological characters are similar among them and different with respect to other populations. The main aim of this study is to compare cranial morphology between African pygmies and non-pygmies populations from Equatorial Africa derived from both the Eastern and the Western regions in order to test if the greatest morphological difference is obtained in the comparison between pygmies and non-pygmies. Thirty three-dimensional (3D) landmarks registered with Microscribe in four cranial samples (Western and Eastern pygmies and non-pygmies) were obtained. Multivariate analysis (generalized Procrustes analysis, Mahalanobis distances, multivariate regression) and complementary dimensions of size were evaluated with ANOVA and post hoc LSD. Results suggest that important cranial shape differentiation does occur between pygmies and non-pygmies but also between Eastern and Western populations and that size changes and allometries do not affect similarly Eastern and Western pygmies. Therefore, our findings raise serious doubt about the fact to consider African pygmies as a homogenous group in studies on skull morphology. Differences in cranial morphology among pygmies would suggest differentiation after divergence. Although not directly related to skull differentiation, the diversity among pygmies would probably suggest that the process responsible for reduced stature occurred after the split of the ancestors of modern Eastern and Western pygmies.

Developmental covariation of human vault and base throughout postnatal ontogeny

In the present study, we analyzed postnatal ontogenetic integration among morphological traits of the human neurocranium. Particularly, the covariation between the vault and the base during postnatal life was assessed. Since the association between these regions may depend on the generalized change produced by allometry, we tested its effect on their covariation. On a sample of adults and subadults ranging from 0 to 31 years, 3D coordinates of neurocranial landmarks and semilandmarks were digitized and geometric morphometric technics were applied. Main aspects of shape variation were examined using Principal Components analysis. Covariation between the vault and the base was examined by Partial Least Squares analysis. According to our results, the vault and the base covary strongly during postnatal ontogeny and their relation depends largely on allometry. Two size variables were studied: centroid size, which was obtained from the recorded morphometric points, and endocranial volume, taken as an estimation of brain size. Although growing brain was found to be a developmental process that contributes to covariation among neurocranial traits, there would be other factors that exert their influence during ontogeny. These results lead to reconsider cranial morphological evolution taking into account the developmental constraints given by ontogenetic patterns of integration and reinforcing the idea that in human evolution a suite of relevant characters may be fuelled by few developmental processes.

An ontogenetic approach to facial variation in three Native American populations.

Various explanations have been formulated regarding high levels of craniofacial variation among Native American populations but the contribution of developmental processes to the establishment of these patterns of variation remains unknown. In this study, we compare facial morphology in ontogenetic series of three Native South American populations, one hunter-gatherer group and two farmer groups, in order to test the null hypothesis that indicates that the pattern of facial differentiation between populations does not change during ontogeny. If diet-related factors contribute to outline facial morphology, it is likely to find greater differences between hunter-gatherer and both farmer groups than between two groups of farmers and this differentiation is expected to increase with age, especially in those structures that are influenced by the mechanical load of mastication. According to our results, hunter-gatherers clearly differ from the two groups of farmers. Non-heritable factors linked to diet, such as nutritional content of food, may increase differentiation across ontogeny in some cases. However, as hunter-gatherers were clearly separated from farmer populations during entire postnatal ontogeny, an important proportion of size variation may not necessarily reflect eco-sensitive changes. Consequently, the hypothesis cannot be completely rejected.

Envejecimiento, pérdida dentaria y cambios craneofaciales/Aging, tooth loss and craneofacial changes

RESUMEN Este trabajo se centra en el analisis de cambios osteoartrosicos observados en esqueletos del cementerio de Rincon Chico 21 (Santa Maria, Catamarca), con el objeto de intentar la reconstruccion de los habitos corporales mas probables y explorar su vinculacion con eventuales divisiones del trabajo en la poblacion que genero este cementerio precolombino. Las manifestaciones osteoartrosicas en los principales sistemas articulares de 56 individuos adultos de ambos sexos fueron registradas, analizadas y comparadas. Los resultados sugieren que en esta comunidad con una economia de subsistencia principalmente basada en la practica de agricultura de regadio y pastoreo de camelidos (Desarrollos Regionales), habria existido una division de tareas y/o actividades potencialmente relacionadas con el sexo de los individuos. Asimismo, los analisis estadisticos aplicados entre los grupos etarios considerados estarian indicando que la edad constituiria un factor determinante en la expresion final de la enfermedad degenerativa articular tanto en las articulaciones de los miembros inferiores como en las del esqueleto axial. ABSTRACT This research is centered on the skeletal analysis of osteoarthritic changes observed in individuals from Rincon Chico 21, a prehistoric burial site at Santa Maria, Catamarca, Argentina. The aim was to try the reconstruction of the most probable corporal behaviours, as well as the possible relationships with labour divisions among individuals from the population that generated the prehistoric cemetery. Osteoarthritic manifestations on the main articular systems of 56 systematically excavated adult skeletons of both sexes were registered, analyzed and compared. Results suggested that in this prehistoric community, with subsistence economy based on agriculture and pastoralism (Regional Developments Period), there may have existed a sexual division of the daily activities. In addition, the results of the statistical analysis applied among the age groups indicate that the age would be an important factor for determining the final expression of the degenerative joint disease, both in the joints of the lower extremities and in the axial skeleton.RESUMEN El estudio de las poblaciones humanas antiguas es complejo y requiere de un enfoque interdisciplinario. La arqueologia argentina esta promoviendo el desarrollo de nuevas lineas de evidencias que incluyen espacios muy activos de interaccion con la biologia. Numerosos estudios biologicos se efectuan sobre los depositos sedimentarios asociados al contexto arqueologico. Los sedimentos asociados a los restos humanos constituyen un recurso de informacion poco explorado y en general, escasamente contemplado en el diseno previo de la excavacion. El presente trabajo aborda el examen de sedimentos de foramenes sacrales de esqueletos humanos pertenecientes al Museo Regional Monsenor Fagnano, Tierra del Fuego, una clase de material arqueologico poco estudiado. La recuperacion de rotiferos, artropodos y parasitos justifica el esfuerzo de muestreo sobre materiales sin asignacion temporal y con escasa referencia espacial. Se puede concluir que el estudio de microfosiles presentes en este tipo de deposito permite maximizar la informacion obtenida del registro bioarqueologico debido a que albergan valiosa informacion paleoambiental, bioantropologica y tafonomica. Asi, el estudio exhaustivo y no destructivo de las muestras arqueologicas resulta un punto crucial en la estrategia de investigacion. ABSTRACT The study of ancient human populations is complex and requires an interdisciplinary approach. The Argentinean archaeology is promoting the development of new research fields, including areas of active interaction with biology. Numerous biological studies are conducted on the sedimentary deposits in association to the archaeological context. The sediments associated to human remains constitute an unexplored source of information. Nevertheless, this material is frequently overlook during excavations and/or insufficient number of samples are taken. The present study analyzes the sediments found in sacral foramina of human skeletons belonging to the Monsenor Fagnano Regional Museum, Tierra del Fuego this is a kind of archaeological material rarely studied. The recovery of rotifers, arthropods and parasites justified the sampling effort on this unusual sediments characterized by a low temporary and spatial reference. It can be concluded that the study of microfossils found in this type of deposit maximized the information obtained from the bioarchaeological registry because it harbors valuable palaeoenvironmental, bioanthropological and taphonomic data. Therefore, the exhaustive and non-destructive study of the archaeological samples is a crucial point in the research strategy