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, 99 (3), 1134-9

The Evolution and Development of Cranial Form in Homosapiens

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The Evolution and Development of Cranial Form in Homosapiens

Daniel E Lieberman et al. Proc Natl Acad Sci U S A.

Abstract

Despite much data, there is no unanimity over how to define Homo sapiens in the fossil record. Here, we examine cranial variation among Pleistocene and recent human fossils by using a model of cranial growth to identify unique derived features (autapomorphies) that reliably distinguish fossils attributed to "anatomically modern" H. sapiens (AMHS) from those attributed to various taxa of "archaic" Homo spp. (AH) and to test hypotheses about the changes in cranial development that underlie the origin of modern human cranial form. In terms of pattern, AMHS crania are uniquely characterized by two general structural autapomorphies: facial retraction and neurocranial globularity. Morphometric analysis of the ontogeny of these autapomorphies indicates that the developmental changes that led to modern human cranial form derive from a combination of shifts in cranial base angle, cranial fossae length and width, and facial length. These morphological changes, some of which may have occurred because of relative size increases in the temporal and possibly the frontal lobes, occur early in ontogeny, and their effects on facial retraction and neurocranial globularity discriminate AMHS from AH crania. The existence of these autapomorphies supports the hypothesis that AMHS is a distinct species from taxa of "archaic" Homo (e.g., Homo neanderthalensis).

Figures

Figure 1
Figure 1
Untransformed factor scores of external linear measurements (see Materials and Methods) that quantify most of the proposed diagnostic cranial characters of AMHS in Table 1. Variables are: 1, frontal angle (FRA); 2, parietal angle (PAA); 3, occipital angle (OCA); 4, vault width relative to height (VWH); 5, canine fossa depth (CFD); 6, vault height relative to length (VHL); and 7, browridge size/shape. Sample includes recent and fossil AMHS crania (see Materials and Methods). Variables outside the shaded box have factor loadings greater than 0.50. Factor 1 (which accounts for 26% of variance) separates variables that quantify neurocranial globularity; factors 2 and 3 (which together account for 35% of the variance) separate variables related to facial retraction. Factors from combined AMHS and AH samples (not shown here) show a similar pattern, but account for more sample variance.
Figure 2
Figure 2
Geometric morphometric comparisons of AH and AMHS cranial form. (A and B) TPS analysis based on least-squared superimposition (see Materials and Methods) of modern human (target) and Broken Hill (warp, in green; A), and Guattari (warp, in green; B). Landmarks used in TPS: sella, sphenoidale, PM point, foramen cecum, anterior nasal spine, nasion, glabella, bregma, lambda, opisthocranion, the most inferoposterior midline point on frontal squama above glabella (frontex), the midline point of greatest elevation between nasion and bregma (metopion), and the midline point of greatest elevation between bregma and lambda (see Materials and Methods for definitions). Arrows indicate basicranial flexion in warp. (C and D) EDMA of four modern humans versus Broken Hill and Bodo (C) and Guattari and Gibraltar 1 (D). Red lines indicate scaled linear distances ≥10% longer in AMHS than warp crania; blue lines indicate scaled linear distances ≥10% shorter in AMHS than warp crania; dashed lines indicate linear distances calculated by using only Broken Hill (C) or Guattari (D) from a smaller subset of landmarks. Note that the PM point, the most anterior point on the greater wings of the sphenoid, lies off the midsagittal plane.
Figure 3
Figure 3
Ontogenetic TPS and EDMA analyses of cranial growth in Pan and Homo (see Materials and Methods for details). Outlines are selected specimens (targets in black, warps in green). (A) P. troglodytes stage II (target), stage I (warp). (B) P. troglodytes stage III (target), stage II (warp). (C) H. sapiens stage II (target), stage I (warp). (D) H. sapiens stage III (target), stage II (warp). (E) Stage III H. sapiens (target), stage III P. troglodytes (warp). The TPS analysis is based on only basicranial and facial landmarks: basion, prosthion, anterior nasal spine, nasion, glabella, opisthocranion, sella, pituitary point, sphenoidale, posterior maxillary plane point, foramen cecum, orbitale, and posterior nasal spine. Superimposed on TPS are EDMA results: red lines indicate scaled linear distances that are significantly longer in target than warp crania; blue lines indicate scaled linear distances that are significantly shorter in target than warp crania.

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