The Neandertal nature of the Atapuerca Sima de los Huesos mandibles

Early Neanderthal mandibular remains from Baume Moula-Guercy (Soyons, Ardèche)

We provide an ontogenetically-based comparative description of mandibular remains from Last Interglacial deposits (MIS 5e) at Baume Moula-Guercy and examine their affinities to European and Middle Eastern Middle-to-Late Pleistocene (≈MIS 14-MIS 1) Homo. Description of the M-G2-419 right partial mandibular corpus with M1-3 (15-16.0 years ±0.5 years) and mandibular fragments M-F4-77 and M-S-TNN1 is with reference to original fossils, casts, CT scans, literature descriptions, and virtual reconstructions. Our comparative sample is ontogenetically based and divided into a Preneanderthal-Neanderthal group and a Homo sapiens group. These groups are subdivided into (1) Preneanderthals (≈MIS 14-9), Early Neanderthals (MIS 7-5e), and Late Neanderthals (MIS 5d-3), and (2) Middle (MIS 5) and Upper (MIS 3-Pre-MIS 1) Paleolithic and recent H. sapiens. Standard techniques were employed for developmental age and sex determinations and measurements. The M-G2-419 mandible possesses corpus features that link it most closely with the Sima de los Huesos Preneanderthal and Early Neanderthal groups. These include mental foramen position, number, and height on the corpus, anterior marginal tubercle position, and mylohyoid line orientation. Metrically, the M-G2-419 mandibular corpus is small relative to adults in all groups, but the thickness/height relationship is like the adult condition. The thickness of the corpus is more like Neanderthal children than adolescents. Molar crown features suggest affinities with the Preneanderthal-Neanderthal group. The Moula-Guercy mandibles possess a combination of Neanderthal-associated features that provides insights into MIS 7-5e paleodeme variation and the timing of appearance of MIS 5d-3 Neanderthal facial features.

The Cranium I: Neurocranium

The Sima de los Huesos (SH) site has provided a significant collection of hominin remains, including numerous cranial fragments, which have contributed to our understanding of the MP human population. The taxonomic classification of the SH hominins remains a topic of debate, with some studies suggesting a close relationship to Neandertals based on nuclear DNA analysis. The cranial morphology of the SH specimens exhibits a mix of Neandertal-like features and primitive traits observed in earlier Homo populations, providing insights into the evolutionary pattern of the Neanderthal lineage. This study focuses on the neurocranial traits of the SH population and describes three previously undescribed cranial individuals. The SH cranial collection now comprises 20 nearly complete crania, representing approximately two-thirds of the estimated population size. The analysis of the SH population reveals variations in robustness, frontal torus development, sagittal keeling, and occipital torus morphology, which may be related to sexual dimorphism and ontogenetic factors. The suprainiac region exhibits notable ontogenetic changes, while suture obliteration patterns do not strictly correlate with dental age. Metric measurements, particularly cranial breadths, highlight significant intrapopulation variation within the SH sample. Compared with other Middle Pleistocene (MP) hominins, the SH cranial vault displays archaic characteristics but differs from Homo erectus and Neandertals. The SH individuals have relatively short and tall cranial vaults, distinguishing them from other MP fossils. These findings contribute to our understanding of the MP human populations and their evolutionary trajectories.

Fusion of the occipitomastoidal synchondrosis as a developmental marker in the Sima de los Huesos Crania (Atapuerca, Spain)

The basicranium contains multiple synchondroses potentially informative for estimating the developmental stage of individuals. The basilar synchondrosis has been routinely used for this purpose in bioarchaeological, forensic and paleoanthropological research, and studies carried out in modern human populations have shown a close relationship between the fusion of the occipitomastoidal synchondrosis and developmental processes. This synchondrosis articulates the jugular process of the occipital bone with the jugular surface of the temporal bone. As the process of fusion of the synchondrosis progresses, the jugular surface undergoes a series of alterations whose study allows to establish the state of fusion of the synchondrosis when the individual died. The extraordinary preservation of the jugular surface in a large number of individuals represented in the fossil hominin sample from the middle Pleistocene site of the Sima de los Huesos (SH) has made it possible to carry out the first systematic study to assess the usefulness of occipitomastoidal synchondrosis in the establishment of the state of development in fossil hominins. Our results show that the complete closure of the occipitomastoidal synchondrosis occurred toward the end of the growth period in the SH fossils. This result opens up the possibility of using it to determine the developmental stage of fossil hominins for which no other information is available, such as the state of the dentition or the degree of closure of the basilar synchondrosis. This has allowed us to infer a state of development for three SH crania where it could not previously be established with certainty.