The relevance of late MSA mandibles on the emergence of modern morphology in Northern Africa

Abstract

North Africa is a key area for understanding hominin population movements and the expansion of our species. It is home to the earliest currently known Homo sapiens (Jebel Irhoud) and several late Middle Stone Age (MSA) fossils, notably Kébibat, Contrebandiers 1, Dar-es-Soltane II H5 and El Harhoura. Mostly referred to as "Aterian" they fill a gap in the North African fossil record between Jebel Irhoud and Iberomaurusians. We explore morphological continuity in this region by quantifying mandibular shape using 3D (semi)landmark geometric morphometric methods in a comparative framework of late Early and Middle Pleistocene hominins (n = 15), Neanderthals (n = 27) and H. sapiens (n = 145). We discovered a set of mixed features among late MSA fossils that is in line with an accretion of modern traits through time and an ongoing masticatory gracilization process. In Northern Africa, Aterians display similarities to Iberomaurusians and recent humans in the area as well as to the Tighenif and Thomas Quarry hominins, suggesting a greater time depth for regional continuity than previously assumed. The evidence we lay out for a long-term succession of hominins and humans emphasizes North Africa's role as source area of the earliest H. sapiens.

Figure 1

Kébibat and Aterian mandibular specimens.

Figure 2

Map with North African sites mentioned in the text. 1 Sidi Abderrahman, 2 Thomas Quarries, 3 Grotte des Contrebandiers, 4 El Harhoura II, 5 Dar-es-Soltane, 6 Kébibat, 7 Salé, 8 Jebel Irhoud, 9 Taforalt, 10 Tighenif, 11 Afalou Bou Rhummel. Topographic map taken from https://www.naturalearthdata.com/ and edited in PDF-XChange Editor v. 8 (PDF-XChange Co. Ltd, Bolney).

Figure 3

Principal component (PC) analyses of the pooled samples of the mandible (n = 166) and corpus (n = 192) data sets in shape space. Warps of PC extremes are displayed in grey (PC1), in bone color (PC2) and red (PC3) for ± 3 SD. They illustrate shape changes that drive mandibular variation along each PC.

Figure 4

Mean shapes of African late Early/Middle Pleistocene hominins, early Homo sapiens, and later H. sapiens (Iberomaurusians/Natufians/ancient sub-Saharans/Upper Paleolithic/Holocene) warped onto a 3D surface model of an individual from the respective group (a) and as wireframes (b).

Figure 5

Box plots depicting centroid size for each group in each data set. Horizontal lines represent the median of each group. Boxes show the interquartile range (IQR, 25th to 75th percentile). Whiskers extend to 1.5 times IQR, but minimum to the lower/upper 25% of the data.

Figure 6

Superimpositions in Procrustes space of the reconstructed Tighenif 2 (dark gray), Kébibat (orange), the reconstructed Dar-es-Soltane II 5 (green), and Taforalt XX (blue).

Figure 7

Superimpositions in Procrustes space of the original Irhoud 11 (pink), Thomas I Gh10717 (white), Dar-es-Soltane II 5 (green), El Harhoura (violet), Taforalt XVIII (turquoise), and a reconstructed version of Irhoud 11 (pink transparent).