Postnatal craniofacial ontogeny in neandertals and modern humans.

OBJECTIVES Neandertals and humans are closely related but differ noticeably in adult morphology. Previous work has been equivocal as to the contribution of postnatal growth and development to these differences. Due to disparate preservation, most analyses focus on specific anatomies, reconstructed fossils, or limited sample sizes. The objective of this research is to highlight the importance of postnatal growth in expressing Neandertal-human distinctions in the craniofacial skeleton, using a large and unreconstructed Neandertal sample. MATERIALS/METHODS A resampling approach is utilized to compare relative size change in 20 craniofacial dimensions between Neandertals (n = 42) and humans (n = 262). The large number of immature Neandertal samples within and between dental stages provides the necessary variation to test for growth differences. Nested resampling using human-human comparisons assesses the likelihood of observing human-Neandertal growth differences under the null hypothesis of similar ontogenetic variation. RESULTS Humans and Neandertals undergo comparable levels of overall size change. However, we identify growth differences for a number of traits, helping explain some of the unique features of this fossil taxon. Nested resampling shows it is unlikely that a Neandertal-like maturation would be observed in a random ontogenetic sample of humans. DISCUSSION Growth during adolescence appears to be fundamental in the expression of some Neandertal anatomies. Neandertal upper facial and nasal breadths appear to have expanded rapidly after puberty to account for differences between preadolescents and adults, and Neandertals and humans. Mandibular growth differences may relate to anterior tooth use to process foods and paramastication during Neandertal maturation.