New methodology to reconstruct in 2-D the cuspal enamel of modern human lower molars

Objectives In the last years different methodologies have been developed to reconstruct worn teeth. In this article, we propose a new 2-D methodology to reconstruct the worn enamel of lower molars. Our main goals are to reconstruct molars with a high level of accuracy when measuring relevant histological variables and to validate the methodology calculating the errors associated with the measurements. Methods This methodology is based on polynomial regression equations, and has been validated using two different dental variables: cuspal enamel thickness and crown height of the protoconid. In order to perform the validation process, simulated worn modern human molars were employed. The associated errors of the measurements were also estimated applying methodologies previously proposed by other authors. Results The mean percentage error estimated in reconstructed molars for these two variables in comparison with their own real values is −2.17% for the cuspal enamel thickness of the protoconid and −3.18% for the crown height of the protoconid. This error significantly improves the results of other methodologies, both in the interobserver error and in the accuracy of the measurements. Conclusions The new methodology based on polynomial regressions can be confidently applied to the reconstruction of cuspal enamel of lower molars, as it improves the accuracy of the measurements and reduces the interobserver error. The present study shows that it is important to validate all methodologies in order to know the associated errors. This new methodology can be easily exportable to other modern human populations, the human fossil record and forensic sciences.

Early Pleistocene hominin deciduous teeth from the Homo antecessor Gran Dolina-TD6 bearing level (Sierra de Atapuerca, Spain)

Objectives. During the last 13 years, the late Early Pleistocene Gran Dolina-TD6-2 level (Sierra de Atapuerca, northern Spain) has yielded an additional sample of 26 dental specimens attributed to Homo antecessor. In this report, we present a descriptive and comparative study of the six deciduous teeth. Methods. We provide external and internal morphological descriptions following classical terminology, as well as the mesiodistal and buccolingual measurements of the teeth. The internal morphology was described by means of micro-CT technique. Results. The TD6 deciduous teeth preserve primitive features regarding the Homo clade, such as the presence of styles in lower and upper canines and developed anterior and posterior foveae in the dm2. However, other features related to the complexity of the crown morphology (e.g., cingulum) are not present in this sample. Furthermore, the great reduction of the talonid of the dm1s is also noteworthy. Despite the limited comparative evidence, the presence of a remarkably well-developed tuberculum molare in the dm1 and dm1s from TD6 can be also considered a derived feature in the genus Homo. The TD6 hominins exhibit dental dimensions similar to those of other Pleistocene hominins. The dm1s are buccolingually elongated and the buccolingual diameter of ATD6-93 is the largest recorded so far in the Homo fossil record. Conclusions. This study expands the list of plesiomorphic features of H. antecessor, and provides some information on the evolutionary status of this species. However, the identification of some advanced traits evinces a step towards the derived morphology of European Pleistocene teeth. The study of the deciduous dentition confirms the mosaic pattern of H. antecessor morphology revealed in previous studies of this hominin sample.

New data on the sexual dimorphism of the hand stencils in El Castillo Cave (Cantabria, Spain)

The determination of the sex of the individuals who placed their hands on cave walls in order to leave the stenciled paintings of their hands, has been the subject of considerable debate in recent years. Many research projects have been carried out with varied results. This study has attempted to obtain new data through an experimental approach that is then applied to the prehistoric hand stencils in El Castillo Cave. In the experiment, 77 samples (hand stencils) of western adults from the Iberian Peninsula, 46 women and 31 men, were taken. For each modern individual (22 women and 18 men), both the stencils and the real size of their hands were measured. This data was then compared with the Paleolithic stencils to determine whether there was a range of variation between the negative image and the actual hand. The measurements taken into account were the general hand length, index finger length and ring finger length. Discriminatory statistical analysis was used for the experimental work and the measurements collected in the field. In the data obtained in the experimental study, significant differences were observed in the length of male and female fingers, but not in the ring fingers themselves. Discriminant analyses show that it is the absolute finger lengths and not the ring fingers that are able to discriminate between men and women. By applying this function to 21 stenciled hands in El Castillo Cave, it was found that 11 belong to women and 10 to men, indicating equal gender representation. Three of the 21 hands may be wrongly sexed according to the discriminant function. However, there is a significant difference between the real finger measurements and the measurements of their stencils in the experimental study, as the negative images overestimate the real values.

Perikymata numbers and enamel extension rates in the incisors of three archaeological modern human populations from two caves located in Spain: Maltravieso Cave (Cáceres) and Mirador Cave (Burgos)

A number of authors have studied the variability of total perikymata counts on permanent incisors in different modern human populations, finding that some populations show a significantly lower number of perikymata than others. However, little is known about the overall variability of these traits in archaeological populations of modern humans. Our aim was to broaden the available data on total perikymata counts on incisors, and to further discuss enamel extension rate variability in modern human incisors. Our sample consisted of 15 incisors from three different archaeological populations belonging to the Holocene: two populations from Mirador Cave (Sierra de Atapuerca, Burgos) assigned to two different chronological periods, and a population from Maltravieso Cave (Cáceres). We refer to these populations as the MTV–MIR sample. Perikymata were counted from several images obtained using an environmental scanning electron microscope (ESEM). Our results suggest the total number of perikymata of the MTV–MIR incisors fall most comfortably within the distribution of counts reported for modern Europeans and Inuit rather than those representing southern African samples of incisors. Furthermore, the percentage of the perikymata numbers in the last five deciles into which the crowns were divided (the cervical half) did not show statistically significant differences when compared to the other modern human populations. This suggests that enamel extension rates among modern human incisors share a common pattern, which might differ from that present in other species. More data from other modern and archaeological sub-Saharan African samples are needed to test whether low perikymata counts are exclusive to the southern African group or are indeed truly representative of sub-Saharan African populations as a whole today and in the past.

Homo antecessor: The state of the art eighteen years later

It is eighteen years since the human fossils recovered from the TD6 level of the Gran Dolina cave site, in Sierra de Atapuerca (Burgos, northern Spain) were assigned to a new hominin species, Homo antecessor. This review summarizes the main results obtained from the study of these fossils during this period. The increase of the African and Eurasian fossil record, as well as the application of new methodological approaches, has led to competing interpretations about its hypothetical phylogenetic position and possible evolutionary scenarios. At present, we can argue that this species is defined by a unique mosaic of primitive traits for the Homo clade, a certain number of derived features present in modern humans, a significant suite of derived features shared with Neandertals and their ancestors in the European Middle Pleistocene (in particular with the Atapuerca-Sima de los Huesos hominins), and some derived features shared with the Chinese Middle Pleistocene hominins. From this evidence, we suggest that a speciation event could have occurred in Africa/Western Eurasia, originating a new Homo clade. Homo antecessor, most probably dated to the MIS 21, could be a side branch of this clade placed at the westernmost region of the Eurasian continent.

Level TE9c of Sima del Elefante (Sierra de Atapuerca, Spain): A comprehensive approach

Level TE9c of the Sima del Elefante site (Sierra de Atapuerca, Spain) is one of the oldest sites with evidence of human occupation in western Europe. We began excavating level TE9c in 2003, and the work there continues today. The studies of the archaeology, palaeontology and geology from this locality have provided an indispensable dataset with which to capture a picture in the scenario of the origin of humans in Europe. Based on these data, we raise and discuss several topics, such as the possible origin of the lineage of the first hominins that inhabited western Europe; their capacity to have active hunting or scavenging abilities; whether their subsistence strategies were successful; and what the environment and habitats where these hominin groups settled was like. The aim of this paper is to present the results and discussions obtained from the research team and to establish the primary features of early human occupations in southwestern Europe. Tentatively, we may conclude, based on the events recorded at TE9c, that the first humans were in the Iberian peninsula at around 1.2 Ma they used the caves of the Sierra de Atapuerca as shelters probably during their hunting activities; the cavities were surrounded by Mediterranean forest, rivers and water ponds, and varied habitats as suggested by the rich and diverse assemblage of fossils of vertebrates (fish, amphibians and reptiles, birds, large and small mammals); where humans possibly caught what they found in the surroundings.

Virtual reconstruction of the Early Pleistocene mandible ATD6-96 from Gran Dolina-TD6-2 (Sierra De Atapuerca, Spain)

Objectives In this report, we present a further study of the late Early Pleistocene ATD6-96 human mandible, recovered from the TD6-2 level of the Gran Dolina cave site (Sierra de Atapuerca, northern Spain) and attributed to Homo antecessor. Methods ATD6-96 consists of a left half of a gracile mandible of an adult individual with the premolars and molars in place that is broken at the level of the lateral incisor-canine septum. The present analysis is based on a virtual reconstruction of the whole mandible by means of computed tomography (CT). We have reconstructed the symphysis using information from a modern human sample, as well as from a wide sample composed of several Homo specimens. Results This research has allowed us to record new variables with taxonomic and phylogenetic interest. We have estimated the length/width index of the alveolar arcade, as well as the percentage of the arcade length with regard to the total length. The latter confirms that ATD6-96 shares with all African and Asian Homo species a primitive structural pattern, as it was established in previous studies. In constrast, the length/width index of the alveolar arcade in the H. antecessor specimen is close to the mean values of Neandertals and the Atapuerca-Sima de los Huesos hominins. Conclusions H. antecessor is derived regarding the shape of the mandibular alveolar arcade within the genus Homo and points to an early divergence from contemporaneous African populations. Our results also ratify the affinities of H. antecessor with Neanderthals, although the precise relationship with this lineage needs further research. Am J Phys Anthropol 159:729–736, 2016. © 2015 Wiley Periodicals, Inc.

Brains, teeth and life histories in hominins: a review

The role of the brain in the somatic development, as well as in the establishment of the different variables of the life history pattern in vertebrates has been largely debated. Moreover, during the last thirty years, dental development has been used as a good proxy to infer different aspects of the life history in hominins, primarily due to the correlation that exists between age at first molar eruption and brain size in the order Primates. We review these questions using what is known about brain growth and maturation, dental development and life history pattern, mainly in Homo sapiens and Pan troglodytes. It has been assumed that the brain represents the pace-maker of our development. However, we consider that our particular phenotype is the result of a hierarchical genetic program modulated by epigenetic and environmental factors. The particular bauplan of any kind of organisms (e.g. primates) may explain the high correlation observed between different variables of its life history pattern, brain size or dental development. However, the correlation of these variables seems to be less reliable when dealing with low-rank taxonomical categories (i.e., species). We suggest that, while there is likely some relationship between the rate of somatic development and tooth development, our brain size and maturation (and, by extension, those of other species of the genus Homo) have derived towards a particular trajectory, with a unique pattern of prenatal and postnatal time and rate of growth and, particularly, with remarkable slow brain maturation. We suggest that extremely slow brain maturation could be a very recent acquisition of the last H. sapiens populations. Furthermore, our review of the literature suggests caution in drawing conclusions about aspects of the life history of the hominins from the information we can obtain from dental development in fossil specimens.

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. Am J Phys Anthropol 2012. © 2012 Wiley Periodicals, Inc.