Susana Sarmiento

Geometric morphometric analysis of the crown morphology of the lower first premolar of hominins, with special attention to Pleistocene Homo

This article is the third of a series that explores hominin dental crown morphology by means of geometric morphometrics. After the analysis of the lower second premolar and the upper first molar crown shapes, we apply the same technique to lower first premolar morphology. Our results show a clear distinction between the morphology seen in earlier hominin taxa such as Australopithecus and African early Homo, as well as Asian H. erectus, and more recent groups such as European H. heidelbergensis, H. neanderthalensis, and H. sapiens. The morphology of the earlier hominins includes an asymmetrical outline, a conspicuous talonid, and an occlusal polygon that tends to be large. The morphology of the recent hominins includes a symmetrical outline and a reduced or absent talonid. Within this later group, premolars belonging to H. heidelbergensis and H. neanderthalensis tend to possess a small and mesiolingually-displaced occlusal polygon, whereas H. sapiens specimens usually present expanded and centered occlusal polygons in an almost circular outline. The morphological differences among Paranthropus, Australopithecus, and African early Homo as studied here are small and evolutionarily less significant compared to the differences between the earlier and later homin taxa. In contrast to the lower second premolar and the upper first molar crown, the inclusion of a larger hominin sample of lower first premolars reveals a large allometric component.

Paleodemography of the Atapuerca: Sima De Los Huesos Hominin Sample: A Revision and New Approaches to the Paleodemography of the European Middle Pleistocene Population

This article analyzes the mortality profiles of two Middle Pleistocene hominin samples, one from the Sima de los Huesos (SH) site in the Sierra de Atapuerca (Spain) (MNI = 28), and another (MNI = 26) selected from various other European sites. In the SH mortality distribution, 64 percent of the individuals died between the ages of 11 and 20 years, but there is only one individual under the age of 10. In the sample from other European sites, there are four individuals under 10, but the number of individuals in the 11-20 year range is lower (39 percent) than in the SH sample. In both samples, the percentage of individuals who died after the age of 30 is very similar (14.3 percent in SH and 11.5 percent at the other sites), and the differences between both distributions (when infants and children are excluded) are not statistically significant. This article considers whether these mortality distributions follow a catastrophic or an attritional pattern. The discussion is presented in the framework of our current knowledge of the life history pattern of the Homo heidelbergensis species and the age structure and mortality profile of living foraging groups.

Gran Dolina-TD6 versus Sima de los Huesos dental samples from Atapuerca: evidence of discontinuity in the European Pleistocene population?

Abstract Comparative analyses between Gran Dolina-TD6 and Sima de los Huesos (SH) dental samples from Sierra de Atapuerca (Spain) suggest that hominins represented by these samples belonged to two very different populations and even to distinct paleospecies. Gran Dolina-TD6 hominins ( Homo antecessor ) have been dated to about 0.8 million years ago (mya), whereas a new radiometric dating of the SH hominins ( Homo heidelbergensis ) suggests an interval of 0.4–0.5 mya for these hominins. Current results as well as the relative temporal closeness between the populations represented by Gran Dolina-TD6 and SH favour a replacement scenario hypothesis (or possibly a crossbreeding scenario) for the Europeans during the early Middle Pleistocene. Although the information available from the European Lower Pleistocene populations is limited (Ceprano and Gran Dolina-TD6), current data are noteworthy and their combination with archaeological evidence will stimulate future discussions on the dynamics of the first European settlements.

Gran Dolina-TD6 and Sima de los Huesos dental samples: Preliminary approach to some dental characters of interest for phylogenetic studies

The Sima de los Huesos (SH) and Gran Dolina-TD6 sites in Sierra de Atapuerca (Spain) have each yielded an impressive fossil hominin sample representing Middle Pleistocene and Late Lower Pleistocene European populations, respectively. Paleontological evidence, paleomagnetic analyses, and radiometric dates (U/Th) suggest an interval of 400 to 500 ky for the SH hominins. At Gran Dolina, radiometric dates (ESR and U-series) combined with paleomagnetic analyses and fossil evidence indicate an age range between 780 and 860 ky for the Aurora Stratum of the TD6 level where the fossil hominins were found. We have assigned the SH hominins to the Homo heidelbergensis species, whereas the TD6 hominins are representative of Homo antecessor, the species named in 1997 (Bermudez de Castro et al., 1997) to accommodate the variability observed in the TD6 fossil human assemblage. Dental collections of the SH and TD6 sites include more than five hundred deciduous and permanent teeth. The detailed description and morphological comparison of the Atapuerca dental samples will be published elsewhere in a near future, but the examination of an extensive human fossil record, has already revealed some dental characters we consider crucial for phylogenetic studies. We describe those characters and provide an overview of their distribution across the hominin fossil dental record. On the basis of these traits we explore some questions about the phylogenetic relationship between TD6 and SH hominins as well as the evolutionary scenario of these two populations.

The Gran Dolina-TD6 Human Fossil Remains and the Origin of Neanderthals

We present a revision of the main features withphylogenetic interest observed in the human fossil remains recovered from the Aurora Stratum of the TD6 level, Gran Dolina site (Sierra de Atapuerca, Spain) that have been assigned to Homo antecessor. Our aim is to test the hypothesis of a possible relationship between this species and the European Middle and early Late Pleistocene hominins, the so-called Neanderthal lineage. Some cranial, postcranial, and dental features are plesiomorphic for the genus Homo and thus, they are not useful for our purpose. Other morphologies are derived with regard to H. ergaster/H. erectus, and TD6 hominins share those traits with modern humans, with Neanderthals or with both lineages. In this context we hypothesize either that there exists a phylogenetic continuity between Homo antecessor and Neanderthals or that both species shared a common ancestor.

Analyse morphométrique comparée des dents humaines de Gran Dolina (TD6) et de Sima de los Huesos d'Atapuerca

Comparative Morphometric Analysis of the Human Dental Samples of Gran Dolina (TD6) and Sima de los Huesos caves sites at Atapuerca. We present a comparative morphometric study of the human dental samples yielded by the Lower Pleistocene site of Gran Dolina (TD6 Aurora Stratum) and the Middle Pleistocene site of Sima de los Huesos (SH) from the Sierra de Atapuerca (Burgos, Spain). The remarkable size and shape differences between the TD6 and SH sample concern, especially, to the anterior vs. posterior size relationship. In the SH hominids, the strong size reduction of the posterior teeth, which reached a degree similar to that of the modern populations, implied the appearance of a set of derived traits, such as the crown and root simplification of the lower premolars, the absence of cingulum, the relative greater size reduction of the lower second premolar and second molar, or the reduction and absence of cusps of the upper and lower molars (hypocone and hypoconulid). The TD6 hominids, in contrast, exhibit a size balance between the anterior dentition and the posterior one, together with the retention of most plesiomorphies for the genus Homo. These observations imply important differences for certain dental development parameters of the two hominid populations, which justifies their taxonomical distinction. On the other hand, the SH hominids and the Neandertalians exhibit a similarity of most dental traits examined, which supports the hypothesis of a reproductive continuity (phyletic evolution) in Europe during the Middle and early Upper Pleistocene.