Le massif facial supérieur d’Homo heidelbergensis Schoetensack, 1908 : l’apport de la morphométrie géométrique

Facial morphologies of Middle Pleistocene Europe: Morphological mosaicism and the evolution of Homo neanderthalensis

The phylogeny of the Middle Pleistocene hominins is a matter of intense scientific debate. Important phylogenetic and taxonomic uncertainties remain, not least due to conflicting results of phylogenetic analyses when methodologies or morphological focus differ. Geography has been proposed to play a key role in Middle Pleistocene hominin diversity, with a European group potentially ancestral to Neanderthals (Homo neanderthalensis) and an African group possibly ancestral to Homo sapiens, but the evidence is equivocal. In this study, we explore the connection between geography and facial morphology in Middle Pleistocene hominins with a particular emphasis on the potential Neanderthal affinities of the European group. Furthermore, to assess the impact of methodology on the results, we use a multimethod approach in which morphological affinities in both facial shape and discrete facial traits are assessed on a dataset consisting of 38 fossil and 20 recent hominin skulls divided into five groups (European and non-European Middle Pleistocene hominins, H. sapiens, H. neanderthalensis, and Homo erectus/Homo ergaster). Two main conclusions emerge from these analyses. First, methodological approach has a marked impact on the recorded pattern of morphological affinity, which may explain result discrepancies among previous studies. Second, this disparity may be caused by morphological mosaicism and polymorphism in the facial region of Middle Pleistocene hominins. The results provide some support for a closer connection between European Middle Pleistocene hominins and Neanderthals in terms of discrete facial traits, but not in overall facial shape, raising questions about the process of evolution of the Neanderthal facial phenotype. As a consequence of these results, we argue that greater attention needs to be paid to clarifying the broader evolutionary processes guiding hominin evolution during this period.

Quantifying hominin morphological diversity at the end of the middle Pleistocene: Implications for the origin of Homo sapiens

OBJECTIVES

The Middle Pleistocene (MP) saw the emergence of new species of hominins: Homo sapiens in Africa, H. neanderthalensis, and possibly Denisovans in Eurasia, whose most recent common ancestor is thought to have lived in Africa around 600 ka ago. However, hominin remains from this period present a wide range of morphological variation making it difficult to securely determine their taxonomic attribution and their phylogenetic position within the Homo genus. This study proposes to reconsider the phenetic relationships between MP hominin fossils in order to clarify evolutionary trends and contacts between the populations they represent.

MATERIALS AND METHODS

We used a Geometric Morphometrics approach to quantify the morphological variation of the calvarium of controversial MP specimens from Africa and Eurasia by using a comparative sample that can be divided into 5 groups: H. ergaster, H. erectus, H. neanderthalensis, and H. sapiens, as well as individuals from current modern human populations. We performed a Generalized Procrustes Analysis, a Principal Component Analysis, and Multinomial Principal Component Logistic Regressions to determine the phenetic affinities of the controversial Middle Pleistocene specimens with the other groups.

RESULTS

MP African and Eurasian specimens represent several populations, some of which show strong affinities with H. neanderthalensis in Europe or H. sapiens in Africa, others presenting multiple affinities.

DISCUSSION

These MP populations might have contributed to the emergence of these two species in different proportions. This study proposes a new framework for the human evolutionary history during the MP.

Virtual ancestor reconstruction: Revealing the ancestor of modern humans and Neandertals

The timing and geographic origin of the common ancestor of modern humans and Neandertals remain controversial. A poor Pleistocene hominin fossil record and the evolutionary complexities introduced by dispersals and regionalisation of lineages have fuelled taxonomic uncertainty, while new ancient genomic data have raised completely new questions. Here, we use maximum likelihood and 3D geometric morphometric methods to predict possible morphologies of the last common ancestor of modern humans and Neandertals from a simplified, fully resolved phylogeny. We describe the fully rendered 3D shapes of the predicted ancestors of humans and Neandertals, and assess their similarity to individual fossils or populations of fossils of Pleistocene age. Our results support models of an Afro-European ancestral population in the Middle Pleistocene (Homo heidelbergensis sensu lato) and further predict an African origin for this ancestral population.