Wednesday, June 7, 2017

New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens

Jean-Jacques Hublin, Abdelouahed Ben-Ncer, Shara E. Bailey, Sarah E. Freidline, Simon Neubauer, Matthew M. Skinner, Inga Bergmann1, Adeline Le Cabec, Stefano Benazzi, Katerina Harvati & Philipp Gunz
Abstract

Fossil evidence points to an African origin of Homo sapiens from a group called either H. heidelbergensis or H. rhodesiensis. However, the exact place and time of emergence of H. sapiens remain obscure because the fossil record is scarce and the chronological age of many key specimens remains uncertain. In particular, it is unclear whether the present day ‘modern’ morphology rapidly emerged approximately 200 thousand years ago (ka) among earlier representatives of H. sapiens[1] or evolved gradually over the last 400 thousand years[2]. Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315 ± 34 thousand years (as determined by thermoluminescence dating)[3], this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established. Furthermore, it shows that the evolutionary processes behind the emergence of H. sapiens involved the whole African continent.

Figure 1 | Facial reconstruction of Irhoud 10. a, b, Frontal (a) and basal
(b) views. This superimposition of Irhoud 10 (beige) and Irhoud 1 (light
blue) represents one possible alignment of the facial bones of Irhoud 10.
Nine alternative reconstructions were included in the statistical shape
analysis of the face (see Methods and Fig. 3). The maxilla, zygomatic bone
and supra-orbital area of Irhoud 10 are more robust than for Irhoud 1.
Scale bar, 20 mm.
 
 
Extended Data Figure 2 | Dental morphology. a, Shape–space PCA
plot of Late Early and Middle Pleistocene archaic Homo, Neanderthals and
RMH M1 crown outlines. The deformed mean crown outlines in
the four directions of the PCs are drawn at the extremity of each axis.
Sample compositions and abbreviations can be found in the Methods.
 


Extended Data Figure 2 | Dental morphology
b. EDJ morphology of the M2 and P4. Top left, the PCA analysis of the
EDJ shape of the M2 places Irhoud 11 intermediate between H. erectus
and RMH (along with other north Africa fossil humans) and distinct from
Neanderthals. Surface models illustrate EDJ shape changes along PC1
(bottom left) and PC2 (top right); the former separating H. erectus from
RMH, Neanderthals and north African EMH and the latter separating
Neanderthals from RMH and north African EMH. Bottom right, a PCA
analysis of the EDJ shape of the P4 groups Irhoud 11 with modern and
fossil humans.
 
Extended Data Figure 3 | Shape analysis of I2 roots. A between-group
PCA shows a complete separation between Neanderthals and a worldwide
sample of recent modern humans based on subtle shape differences.
Irhoud 11 (pink star) plots at the fringes of RMH, close to the EMH from
Contrebandiers 1 (Tem). Colour-coded Procrustes group mean shapes
are plotted in the same orientation as the I2 root surface of Irhoud 11.
Although Irhoud 11 is more similar, overall, to Neanderthals in terms
of root size, its root shape is clearly modern. The H. erectus specimen
KNM-WT 15000 and hypothetical EMH Tabun C2 have incisor root
shapes similar to Neanderthals, suggesting that roots that are labially
more convex than in RMH represent a conserved primitive condition with
limited taxonomical value. Sample compositions and abbreviations can be
found in the Methods.
 
 
Extended Data Figure 4 | Shape analysis of the external vault. a, PC
scores of PC1 and PC2 of external braincase shape in H. erectus, archaic
Middle Pleistocene Homo, geographically diverse RMH and Neanderthals.
Results are consistent with the analysis of endocranial shape (Fig. 3a).
However, several EMH and Upper Palaeolithic specimens fall outside the
RMH variation. This is probably owing to the projecting supraorbital tori
in these specimens.


Extended Data Figure 4 | Shape analysis of the external vault.
b, Shape changes associated with PC1 (two standard
deviations in either direction) shown as thin-plate spline deformation
grids in lateral and oblique view. PC1 captures a contrast between
elongated braincases with projecting supraorbital tori (low scores, in
black) and a more globular braincase with gracile supraorbital tori (high
scores, in red). Sample compositions and abbreviations can be found in the
Methods.
 

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