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Background: There has been a rapid increase in the brain size relative to body size during mammalian evolutionary history. In particular, the enlarged and globular brain is the most distinctive anatomical feature of modern humans that set us apart from other extinct and extant primate species. Genetic basis of large brain size in modern humans has largely remained enigmatic. Genes associated with the pathological reduction of brain size (primary microcephaly-MCPH) have the characteristics and functions to be considered ideal candidates to unravel the genetic basis of evolutionary enlargement of human brain size. For instance, the brain size of microcephaly patients is similar to the brain size of Pan troglodyte and the very early hominids like the Sahelanthropus tchadensis and Australopithecus afarensis. Results: The present study investigates the molecular evolutionary history of subset of autosomal recessive primary microcephaly (MCPH) genes; CEP135, ZNF335, PHC1, SASS6, CDK6, MFSD2A, CIT, and KIF14 across 48 mammalian species. Codon based substitutions site analysis indicated that ZNF335, SASS6, CIT, and KIF14 have experienced positive selection in eutherian evolutionary history. Estimation of divergent selection pressure revealed that almost all of the MCPH genes analyzed in the present study have maintained their functions throughout the history of placental mammals. Contrary to our expectations, human-specific adoptive evolution was not detected for any of the MCPH genes analyzed in the present study. Conclusion: Based on these data it can be inferred that protein-coding sequence of MCPH genes might not be the sole determinant of increase in relative brain size during primate evolutionary history. [ABSTRACT FROM AUTHOR]

Abstract: The fossiliferous area of Toros-Menalla (TM) (Djurab Desert, northern Chad) has yielded one of the richest African mammal faunas of the late Miocene. It is also the place where the earliest known hominin, Sahelanthropus tchadensis, was found. Although more than 300 localities are recorded in that area, previous paleoecological studies focused only on the largest and richest one. The integration of the material from other TM localities, and thus of a significant number of mammal taxa, is crucial to improve the corresponding paleoenvironmental reconstructions. Before such inferences can be drawn, it is necessary to test for the ecological integrity of these mammal assemblages: how many paleocommunities do they represent? The faunal structures of several assemblages selected for their apparent resilience to sampling biases are compared here. The criteria used in the inter-assemblage comparison are ecological diversity, taxonomic structure (taxonomic rank of abundance) and taxonomic composition. Based on multivariate analyses, two groups of TM assemblages can be distinguished. One of them contains the hominin-bearing assemblages. It is taxonomically richer and shows a wider ecological spectrum than its counterpart. The degree of taphonomic alteration undergone by the TM assemblages, as well as the distribution of amphibious mammals among them, suggest different depositional settings for these two groups of assemblages, the richest of which was probably associated with lower hydraulic energy. Overall, it seems that the TM assemblages recorded the same mammal paleocommunity preserved in two contrasted depositional settings. Moreover, the spatial overlap of these assemblages provides further evidence for the mosaic character of the landscape associated with S. tchadensis. [Copyright &y& Elsevier]

ABSTRACT The evolution of the teeth in hominins is characterized by, among other characters, major changes in root morphology. However, little is known of the evolution from a plesiomorphic, ape-like root morphology to the crown hominin morphology. Here we present a study of the root morphology of the Miocene Chadian hominin Sahelanthropus tchadensis and its comparison to other hominins. The morphology of the whole lower dentition (I1-M3) was investigated and described. The comparison with the species Ardipithecus kaddaba and Ardipithecus ramidus indicates a global homogeneity of root morphology in early hominins. This morphology, characterized notably by a reduction of the size and number of the roots of premolars, is a composite between an ape-like morphology and the later hominin morphology. Trends for root evolution in hominins are proposed, including the transition from a basal hominoid to extant Homo sapiens. This study also illustrates the low association between the evolution of tooth root morphology and the evolution of crowns in hominins. Am J Phys Anthropol 153:116-123, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The article discusses issues in the origin of human bipedalism and its importance in the evolution of mankind as of January 2012. Also cited are the various discoveries of fossil hominoid, including the Orrorin tugenensis in Kenya, the Ardipithecus kadabba in Ethiopia, and the Sahelanthropus tchadensis in Chad. Also cited is a study by anatomist Edward Tyson on the anatomies of chimpanzee and humans.

Toumai (Sahelanthropus tchadensis) is, to date, the oldest known hominine. Approximately 7 million years ago, it lived close to the northern shoreline of the paleo Lake Chad, which extended at that time 500 km north of its present location. Here, we describe a new xerine squirrel, Sabara oralacus, gen. et sp. nov., discovered near the site where Toumai was unearthed. Study of associated fauna is essential to evaluate correctly the precise paleoenvironmental affinities of the first African hominines. The new squirrel displays a mosaic of dental and skull characters characterizing either the tribe Xerini or Protoxerini, which makes its taxonomic assignment at the tribe level difficult. From craniodental characters, we hypothesize that S. oralacus was a ground-dweller, digging burrows, probably with an ecological preference for forest to savannah environments associated with hard fruit-bearing trees. [ABSTRACT FROM AUTHOR]

Land water storage plays a fundamental role in the West African water cycle and has an important impact on climate and on the natural resources of this region. However, measurements of land water storage are scarce at regional and global scales and especially in poorly instrumented endorheic regions, such as most of the Sahel, where little useful information can be derived from river flow measurements and basin water budgets. The Gravity Recovery and Climate Experiment (GRACE) satellite mission provides an accurate measurement of the terrestrial gravity field variations from which land water storage variations can be derived. However, their retrieval is not straightforward, and different methods are employed, which results in different water storage GRACE products. On the other hand, water storage can be estimated by land surface modeling forced with observed or satellite-based boundary conditions, but such estimates can be highly model dependent. In this study, land water storage by six GRACE products and soil moisture estimations by nine land surface models (run within the framework of the African Monsoon Multidisciplinary Analysis Land Surface Intercomparison Project (ALMIP)) are evaluated over West Africa, with a particular focus on the Sahelian area. The water storage spatial distribution, including zonal transects, its seasonal cycle, and its and interannual variability, are analyzed for the years 2003-2007. Despite the nonnegligible differences among the various GRACE products and among the different models, a generally good agreement between satellite and model estimates is found over the West Africa study region. In particular, GRACE data are shown to reproduce well the water storage interannual variability over the Sahel for the 5 year study period. The comparison between satellite estimates and ALMIP results leads to the identification of processes needing improvement in the land surface models. In particular, our results point out the importance of correctly simulating slow water reservoirs as well as evapotranspiration during the dry season for accurate soil moisture modeling over West Africa. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the impact of the successive discovery of two early hominids from Mio-Pliocene of Chad (Australopithecus bahrelghazali, nicknamed Abel dated to 3.5Ma and Sahelanthropus tchadensis, nicknamed Toumaï dated to 7Ma) on our understanding of how far back go the roots of mankind and what kind of environment they lived in. These discoveries introduce new geographic and phylogenetic paradigms to explain the African evolution of our prehuman ancestors. [ABSTRACT FROM AUTHOR]

Abstract: This study aimed to reconstruct the environmental conditions that prevailed in the Chadian palaeo-lake basin ca. 7Ma ago based on the feeding preferences of late Miocene Bovidae from Toros-Menalla (Chad). This is a key issue for understanding the circumstances (regional landscapes) under which the earliest known hominid Sahelanthropus tchadensis evolved. A dental mesowear analysis was applied to 117 specimens of bovids representing the four tribes present in the anthracotheriid unit localities: Hippotragini, Reduncini, Antilopini and Bovini. All these bovids fed on grasses, at least partially. Previous analyses and the present results indicate the presence of a mosaic-like environment containing various habitats from grasslands to woodlands in the surroundings of the Chadian lake basin. Indeed, our data support the availability of grass or grass-like plants and therefore open patches in the vicinity of the Chadian palaeo-lake shores. [Copyright &y& Elsevier]

Abstract: The earliest known hominid Sahelanthropus tchadensis Brunet et al., 2002, nicknamed Toumaï, from the Late Miocene (7Ma) of Chad, displays a unique combination of primitive and derived characters which clearly shows that it is probably temporally close to the common ancestor of chimpanzees and humans. The Late Miocene Hominids: Sahelanthropus (Chad), Orrorin (Kenya), Ardipithecus (Ethiopia) are probably the ancestral group of Australopithecins from which the genus Homo appears between 2 and 3Ma and then for the first time widespread in Eurasia. So, Toumaï seven millions years old confirms in a spectacular way the prediction Charles Darwin made in 1871. [Copyright &y& Elsevier]

A partial left femur (TM 266-01-063) was recovered in July 2001 at Toros-Menalla, Chad, at the same fossiliferous location as the late Miocene holotype of Sahelanthropus tchadensis (the cranium TM 266-01-060-1). It was recognized as a probable primate femur in 2004 when one of the authors was undertaking a taphonomic survey of the fossil assemblages from Toros-Menalla. We are confident the TM 266 femoral shaft belongs to a hominid. It could sample a hominid hitherto unrepresented at Toros-Menalla, but a more parsimonious working hypothesis is that it belongs to S. tchadensis. The differences between TM 266 and the late Miocene Orrorin tugenensis partial femur BAR 1002′00, from Kenya, are consistent with maintaining at least a species-level distinction between S. tchadensis and O. tugenensis. The results of our preliminary functional analysis suggest the TM 266 femoral shaft belongs to an individual that was not habitually bipedal, something that should be taken into account when considering the relationships of S. tchadensis. The circumstances of its discovery should encourage researchers to check to see whether there is more postcranial evidence of S. tchadensis among the fossils recovered from Toros-Menalla. [ABSTRACT FROM AUTHOR]