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age); (2) centroid size (S, the extent of the landmark conguration); and (3) taxon (Neanderthal compared to modern human).
In all three analyses, only the rst two statistically independent relative warps (w1 and w2) covary signicantly with age, S and taxon, which together account for about 60% of the total shape variability (see Methods and Supplementary Information for details of relative warp analysis). There are clear patterns of covariation: w1 describes shape variation related to size and age (Figs 1 and 2), whereas w2 describes taxon-specic shape variation (Fig. 1). Each w1w2
coordinate in Fig. 1 corresponds to a specic morphological conguration in physical space, and each vector (arrows along statistically independent relative warps in Fig. 1) indicates a distinct spatial pattern of morphological change. The most important result of the analyses (evident from Fig. 1) is that taxon-specic differences in craniomandibular shape are present by dental stage 2 and remain subsequently unchanged during ontogeny. This indicates that the characteristic morphologies that distinguish both Neanderthals and modern humans develop before dental stage 2, during early post-natal or possibly during prenatal ontogeny. From dental stage 2 onwards, Neanderthals and modern humans follow parallel onto-genetic trajectories along the direction of w1 (Fig. 1), demonstrating a shared spatial pattern of morphological change (Fig. 3). The different lengths of the trajectories in Fig. 1, however, indicate that there are heterochronic differences between the taxa in their post-natal ontogeny. Plots of the relationship between dental age, craniomandibular shape w1 and size S (Fig. 2) show that although
the two taxa follow similar ontogenetic allometries (Fig. 2a), Neanderthals compared to modern humans show rate hyper-morphosis (faster rates of growth and development leading to greater adult values of size and shape) during ontogeny (Fig. 2b,c). In all analyses, the fossil modern human subsample falls within the range of ontogenetic variability displayed by the extant modern human sample. In addition, the Neanderthals analysed here, which sample a long period of time1, exhibit similar within-taxon onto-genetic variability, suggesting long-term stability of the modern human and Neanderthal patterns of ontogeny.
To further explore taxon-specic regional differences in cranial and mandibular growth, Figs 3 and 4 express statistically independent factors w1 and w2 as modications of the Neanderthal/ modern human consensus morphology (computed...