Early Pleistocene human mandible from Sima del Elefante (TE) cave site in Sierra de Atapuerca (Spain): a comparative morphological study

We present a detailed morphological comparative study of the hominin mandible ATE9-1 recovered in 2007 from the Sima del Elefante cave site in Sierra de Atapuerca, Burgos, northern Spain. Paleomagnetic analyses, biostratigraphical studies, and quantitative data obtained through nuclide cosmogenic methods, place this specimen in the Early Pleistocene (1.2-1.3 Ma). This finding, together with archaeological evidence from different European sites, suggests that Western Europe was colonised shortly after the first hominin expansion out of Africa around the Olduvai subchron. Our analysis of the ATE9-1 mandible includes a geometric morphometric analysis of the lower second premolar (LP₄), a combined and detailed external and internal assessment of ATE9-1 roots through CT and microCT techniques, as well as a comparative study of mandibular and other dental features. This analysis reveals some primitive Homo traits on the external aspect of the symphysis and the dentition shared with early African Homo and the Dmanisi hominins. In contrast, other mandibular traits on the internal aspect of the symphysis are derived with regard to African early Homo, indicating unexpectedly large departures from patterns observed in Africa. Reaching the most occidental part of the Eurasian continent implies that the first African emigrants had to cross narrow corridors and to overcome geographic barriers favouring genetic drift, long isolation periods, and adaptation to new climatic and seasonal conditions. Given these conditions and that we are dealing with a long time period, it is possible that one or more speciation events could have occurred in this extreme part of Eurasia during the Early Pleistocene, originating in the lineages represented by the Sima del Elefante-TE9 hominins and possibly by the Gran Dolina-TD6 hominins. In the absence of any additional evidence, we prefer not include the specimen ATE9-1 in any named taxon and refer to it as Homo sp.     

The fossil bat assemblage of Sima del Elefante Lower Red Unit (Atapuerca,Spain): First results and contribution to the palaeoenvironmental approach to the site

The fossil bat assemblage from the Lower Red Unit of Sima del Elefante (TELRU) in Atapuerca (Burgos, Spain) has been exhaustively analysed for the first time. Bat fossil assemblages are of particular relevance to palaeoenvironmental approaches to sites. Here we integrate our new data on the chiropteran fauna with the data provided previously by other authors on the basis of the small-vertebrate assemblages and the palynology of the site. Our results are consistent with the earlier results in that they indicate a generally warmer climate than at present in the area and stable environmental conditions throughout the major part of the TELRU sequence. However, fossil bat assemblages sometimes lead to problems when they are used in landscape reconstruction. These problems are discussed here and should be taken into account in future works.     

Human hyoid bones from the middle Pleistocene site of the Sima de los Huesos (Sierra de Atapuerca, Spain)

This study describes and compares two hyoid bones from the middle Pleistocene site of the Sima de los Huesos in the Sierra de Atapuerca (Spain). The Atapuerca SH hyoids are humanlike in both their morphology and dimensions, and they clearly differ from the hyoid bones of chimpanzees and Australopithecus afarensis. Their comparison with the Neandertal specimens Kebara 2 and SDR-034 makes it possible to begin to approach the question of temporal variation and sexual dimorphism in this bone in fossil humans. The results presented here show that the degree of metric and anatomical variation in the fossil sample was similar in magnitude and kind to living humans. Modern hyoid morphology was present by at least 530 kya and appears to represent a shared derived feature of the modern human and Neandertal evolutionary lineages inherited from their last common ancestor.     

Paleoecological and microenvironmental aspects of the first European hominids inferred from the taphonomy of small mammals (Sima del Elefante,Sierra de Atapuerca,Spain)

Unit TE9 of the Sima del Elefante (Sierra de Atapuerca, Burgos, Spain), where the remains of Homo sp. have been discovered (1.2–1.3 Ma), is also a level rich in small mammals. The taphonomic study of these small vertebrates sheds light on the landscape that provided the setting for the activities of these early hominids and allows us to describe what the cave was like during the formation of the level. Small mammal predators identified in the study indicate that during this period the Sierra de Atapuerca was part of a large biome consisting of semi-open riparian forests with meadows nearby. Postdepositional alterations reveal that the production of fossils took place outside the cave, being transported inside by water currents. During the formation of TE9, the cave presented conditions of high humidity, which made it difficult for hominids to establish occupations inside, although these conditions became somewhat less severe in TE9c, the sublevel where human remains are found.     

Metric and morphological study of the upper cervical spine from the Sima de los Huesos site (Sierra de Atapuerca, Burgos, Spain)

In this article, the upper cervical spine remains recovered from the Sima de los Huesos (SH) middle Pleistocene site in the Sierra de Atapuerca (Burgos, Spain) are described and analyzed. To date, this site has yielded more than 5000 human fossils belonging to a minimum of 28 individuals of the species Homo heidelbergensis. At least eleven individuals are represented by the upper cervical (C1 and C2) specimens: six adults and five subadults, one of which could represent an adolescent individual. The most complete adult vertebrae (three atlases and three axes) are described, measured, and compared with other fossil hominins and modern humans. These six specimens are associated with one another and represent three individuals. In addition, one of these sets of cervical vertebrae is associated with Cranium 5 (Individual XXI) from the site. The metric analysis demonstrates that the Sima de los Huesos atlases and axes are metrically more similar to Neandertals than to our modern human comparative sample. The SH atlases share with Neandertals a sagittally elongated canal. The most remarkable feature of the SH (and Neandertal) axes is that they are craniocaudally low and mediolaterally wide compared to our modern male sample. Morphologically, the SH sample shares with Neandertals a higher frequency of caudally projected anterior atlas arch, which could reflect greater development of the longus colli muscle. In other features, such as the frequency of weakly developed tubercles for the attachment of the transverse ligament of the atlas, the Sima de los Huesos fossils show intermediate frequencies between our modern comparative samples and the Neandertals, which could represent the primitive condition. Our results are consistent with the previous phylogenetic interpretation of H. heidelbergensis as an exclusively European species, ancestral only to H. neanderthalensis.     

Early Pleistocene human humeri from the Gran Dolina-TD6 site (Sierra de Atapuerca, Spain)

In this report, we present a morphometric comparative study of two Early Pleistocene humeri recovered from the TD6 level of the Gran Dolina cave site in Sierra de Atapuerca, northern Spain. ATD6-121 belongs to a child between 4 and 6 years old, whereas ATD6-148 corresponds to an adult. ATD6-148 exhibits the typical pattern of the genus Homo, but it also shows a large olecranon fossa and very thin medial and lateral pillars (also present in ATD6-121), sharing these features with European Middle Pleistocene hominins, Neandertals, and the Bodo Middle Pleistocene humerus. The morphology of the distal epiphysis, together with a few dental traits, suggests a phylogenetic relationship between the TD6 hominins and the Neandertal lineage. Given the older geochronological age of these hominins (ca. 900 ka), which is far from the age estimated by palaeogenetic studies for the population divergence of modern humans and Neandertals (ca. 400 ka), we suggest that this suite of derived "Neandertal" features appeared early in the evolution of the genus Homo. Thus, these features are not "Neandertal" apomorphies but traits which appeared in an ancestral and polymorphic population during the Early Pleistocene.     

Pleistocene human remains and conservation treatments: the case of a mandible from Atapuerca (Spain)

Research on human evolution depends in many cases on the study of fossil remains that have been treated by conservators. Conservation is a discipline with its own principles and methods. Its goal is not only long-term preservation, but also information recovery and the facilitation of research. Therefore, specialists in conservation propose and carry out the interventions, while research requirements must act as a guide in many steps of the process. In this article, we present an example of a strict conservation methodology applied to a human mandible from the Pleistocene site of Gran Dolina (Sierra de Atapuerca, Spain). An extensive diagnostic examination before the intervention included a computer tomography (CT) scan and stereoscopic light microscopy. This paper describes both the intervention and the mechanical preparation in detail. Finally, the intervention is discussed, as well as general conservation techniques. The compiled details show how this interdisciplinary work allowed retention of both the integrity of the specimen and its information. In conclusion, the development of a suitable method of conservation requires collaboration among all the specialists involved in the study of fossil remains.     

Human talus bones from the Middle Pleistocene site of Sima de los Huesos (Sierra de Atapuerca,Burgos, Spain)

Here we present and describe comparatively 25 talus bones from the Middle Pleistocene site of the Sima de los Huesos (SH) (Sierra de Atapuerca, Burgos, Spain). These tali belong to 14 individuals (11 adult and three immature). Although variation among Middle and Late Pleistocene tali tends to be subtle, this study has identified unique morphological characteristics of the SH tali. They are vertically shorter than those of Late Pleistocene Homo sapiens, and show a shorter head and a broader lateral malleolar facet than all of the samples. Moreover, a few shared characters with Neanderthals are consistent with the hypothesis that the SH population and Neanderthals are sister groups. These shared characters are a broad lateral malleolar facet, a trochlear height intermediate between modern humans and Late Pleistocene H. sapiens, and a short middle calcaneal facet. It has been possible to propose sex assignment for the SH tali based on their size. Stature estimates based on these fossils give a mean stature of 174.4 cm for males and 161.9 cm for females, similar to that obtained based on the long bones from this same site.     

Palaeopathology of the Pleistocene specimen D2600 from Dmanisi (Republic of Georgia)

Here we present a detailed palaeopathological study of the hominin mandible D2600 recovered at the Dmanisi site, Republic of Georgia. The Dmanisi assemblage represents the earliest evidence of hominins outside Africa with an age of 1.8 Ma. D2600 is the holotype of Homo georgicus species and its taxonomic assignment is still under debate. Our study reveals severe and unusual dental wear accompanied of extensive root exposure and dental axial migration, periapical abscesses and enamel fractures. In addition, there is evidence of post-eruptive tooth rotation and temporomandibular arthropathy. We propose that the wear pattern observed in this individual is related to a diet with a high intake of fibrous and abrasive foods such as fruits and plants, as it is usually recorded in chimpanzees and gorillas and unlike the wear pattern observed in other Homo specimens of our comparative sample. The rounded occlusal surfaces and highly polished labio-lingual surfaces of D2600 anterior teeth could be mainly the consequence of pre- and/or para-masticatory activities such as gripping and stripping. This type of food would be also the origin of the highly cupped occlusal morphology of the posterior dentition in combination with relatively slight approximal attrition. However, the lesions exhibited by D2600 have not significantly altered the morphology of the mandible and do not prevent a proper taxonomic assessment.     

New foot remains from the Gran Dolina-TD6 Early Pleistocene site (Sierra de Atapuerca, Burgos, Spain)

This paper presents and describes new foot fossils from the species Homo antecessor, found in level TD6 of the site of Gran Dolina (Sierra de Atapuerca, Burgos, Spain). These new fossils consist of an almost complete left talus (ATD6-95) and the proximal three-quarters of a right fourth metatarsal (ATD6-124). The talus ATD6-95 is tentatively assigned to Hominin 10 of the TD6 sample, an adult male specimen with which the second metatarsal ATD6-70+107 (already published) is also tentatively associated. Analysis of these fossils and other postcranial remains has made possible to estimate a stature similar to those of the specimens from the Middle Pleistocene site of Sima de los Huesos (Sierra de Atapuerca, Burgos, Spain). The morphology of the TD6 metatarsals does not differ significantly from that of modern humans, Neanderthals and the specimens from Sima de los Huesos. Talus ATD6-95, however, differs from the rest of the comparative samples in being long and high, having a long and wide trochlea, and displaying a proportionally short neck.