Growth directions of the maxilla in the Sima de los Huesos (SH) and Neanderthals compared to modern humans. This impacts facial growth in at least two ways. (i) Extensive bone deposits over the maxilla in the fossils are consistent with a strong forward growth component (purple arrows); whereas resorption in the modern human face attenuates forward displacement (blue arrow). (ii) Deposition combined with larger developing nasal cavities in the fossils displaces the dentition forward generating the retromolar space characteristic of Neanderthals and also in some SH fossils. Credit: Rodrigo S Lacruz

A new open access paper in Nature Communications, “Ontogeny of the Maxilla in Neanderthals and their Ancestors,” describes for the first time the developmental processes that differentiate Neanderthal facial skeletons from those of modern humans. As may known humans and Neandertals have different faces but recent advances in ancient genetics have brought to light the depth of admixture and raised discussion that maybe we should not consider the two distinct branches of the human family tree. The paper states that based upon facial growth patterns, Neandertals and humans are indeed sufficiently distinct from one another.

The team studied several well-preserved Neandertal child skulls such as the one discovered in 1926 in the British territory of Gibraltar and another from the La Quina site in southwestern France, also excavated in the early 1900s. They also compared Neandertal facial-growth patterns and remodeling with that of four Middle Pleistocene hominin faces of teenagers from the fossil collection of the Sima de los Huesos in north-central Spain. The Sima fossils are considered likely Neandertal ancestors based on both anatomical features and genomic DNA analysis.

The study found that in Neandertals, the facial bone-growth remodeling or the process by which bone is deposited and reabsorbed, forming and shaping the adult skeleton contributed to the development of a prognathic maxilla because of extensive deposits by osteoblasts without a compensatory resorption. This is a process they shared with ancient hominins. This process is in stark contrast to that in human children, whose faces grow with a counter-balance action mediated by resorption taking place especially in the lower part of the face, leading to a flatter jaw relative to Neandertals.