Mes: junio 2023

Sexual dimorphism of deciduous canine dental tissues dimensions of modern human populations

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The dental tissue proportions of human permanent canines are one of only a few sexually dimorphic features that are present in childhood, and therefore offer the opportunity to estimate the sex of immature individuals. This work aims to evaluate for the first time the degree of sexual dimorphism ‍in the three-dimensional (3D) measurements of deciduous canine dental tissues, to assess their potential in sexual assessment. Computed microtomographic techniques have been employed to anal‍yse the maxillary and mandibular deciduous canines of 65 individuals (36 females and 29 males) of known sex and age. The teeth were scanned and the volumes and 3D surface areas of the enamel cup and the dentine–pulp complex were obtained. Our results did not show statistically significant differences in either the absolute or relative dimensions of the enamel and dentine between female and male teeth. We hence conclude that volumes and 3D surface areas of deciduous canine dental tissues do not allow for sex determination, which contrasts with what has been observed in permanent canines by other authors. The differences in the degree of sexual dimorphism in dental tissue proportions be‍tween permanent and deciduous canines seem to be due to a decrease in the intersexual variability of ‍the dentine component dimensions. Since the dentine component is a tissue capable of responding to ‍changes in sex hormone concentration levels, our results might indicate that hormones play a more important role in the development of sexual dimorphism in the permanent dentition than previously thought.

Crown tissue proportions and enamel thickness distribution in early Pleistocene Homo antecessor maxillary premolars (Atapuerca, Spain)

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Objectives Both morphometric and proteomic studies have revealed the close relationship of Homo antecessor with Neanderthals and H. sapiens. Considering this relationship, we aim to characterize the Early Pleistocene Atapuerca-Gran Dolina (TD6) maxillary premolars to test if their pattern of enamel thickness is shared with Neanderthals or H. sapiens. Materials and Methods We employed microcomputed tomography to estimate 2D and 3D tissue proportions in seven H. antecessor maxillary premolars, belonging to two individuals: H1 and H3, and compared them to a sample of extinct and extant Homo populations of African, Asian and European origin (n = 52). Results Our results reveal a different pattern of enamel thickness between the Atapuerca-Gran Dolina two individuals. While TD6-H1 possesses thin-enameled crowns, with a clear affinity with Neanderthals, TD6-H3 exhibits the thick pattern, a trait shared with the majority of fossil hominins and H. sapiens. Discussion This work provides new data on upper premolar enamel thickness in H. antecessor. By documenting both a thin and a thick pattern of enamel thickness in the TD6 sample, we warn about the taxonomic utility of this feature in the characterization of isolated remains. We suggest that the thin enamel condition would have emerged during the Early Pleistocene and it became the most frequent and typical condition in Neanderthals. Possible causes for the pattern observed in TD6 include sexual dimorphism or presence of two populations in the sample; however, population variability is the most plausible explanation with a character expression intermediate between those of Neanderthals and other members of the genus Homo. This interpretation is compatible with the phylogenetic position of H. antecessor close to the ancestor of Neanderthals and H. sapiens.

Early and Middle Pleistocene hominins from Atapuerca (Spain) show differences in dental developmental patterns

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The Bayesian statistical approach considers teeth as forming a developmental module, as opposed to a tooth-by-tooth analysis. This approach has been employed to analyze Upper Pleistocene hominins, including Neandertals and some anatomically modern humans, but never earlier populations. Here, we show its application on five hominins from the TD6.2 level of the Gran Dolina site (Homo antecessor, Early Pleistocene) and the Sima de los Huesos site (Middle Pleistocene) of the Sierra de Atapuerca (Burgos, northern Spain). Our results show an advanced development of the third molars in both populations with respect to modern Homo sapiens. In addition, the Sima de los Huesos hominins differ from H. sapiens and H. antecessor in the relatively advanced development of their second molar. The relative mineralization of I1/M1 in H. antecessor appears to be similar to that of modern humans, as opposed to that of Neandertals, which appear to be unique. These observations, combined with reduced enamel formation times and the advanced development of the third molars, appear to indicate a shorter ontogenetic period in the hominins from Gran Dolina and Sima de los Huesos in comparison to modern human average.

Similarities and differences in the dental tissue proportions of the deciduous and permanent canines of Early and Middle Pleistocene human populations

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The two- and three-dimensional assessment of dental tissues has become routine in human taxonomic studies throughout the years. Nonetheless, most of our knowledge of the variability of the enamel and dentine dimensions of the human evolutionary lineage comes from the study of permanent dentition, and particularly from molars. This leads to a biased view of the variability of these features. Due to their early formation and rapid development, the deciduous teeth allow more simplified inferences regarding the processes involved in the dental tissue development of each group. Therefore, their study could be very valuable in dental palaeohistology. In this research, we have explored the dental tissue proportions of the deciduous canines belonging to some human samples of the Early and Middle Pleistocene. The purpose of this was to discuss the meaning of the similarities and differences observed in their histological pattern, as well as to evaluate the degree of covariance with that observed in the permanent dentition of these populations. Our results show that, although there are some similarities in the dental tissue proportions between the deciduous and permanent canines of the study samples, the two dental classes do not provide a similar or comparable pictures of the dental tissue pattern present in the dentition of fossil hominins. Future works on the dental tissue patterns of the anterior and posterior dentition, including deciduous teeth, of fossil samples, may help to shed light on this hypothesis.

Dental remains of the Middle Pleistocene hominins from the Sima de los Huesos site (Sierra de Atapuerca, Spain): Maxillary dentition

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The Middle Pleistocene site of the Sima de los Huesos (Sierra de Atapuerca, northern Spain) has yielded a considerable number of human fossils during the period 1984–2020. Among them, up to 253 maxillary teeth have been recovered. In this article, we present the description of the eight dental classes of the maxilla following the Arizona State University Dental Anthropology System classification. In addition, we present the mean mesiodistal and buccolingual diameters of these teeth compared to those of Neanderthals and a modern human sample. The morphology of both the anterior and posterior teeth suggests a close relationship of the Sima de los Huesos hominins with the populations of the second half of the Middle Pleistocene of Europe and the Near East, as well as with the so-called classic Neanderthals of Europe. Features with a recognizable taxonomic signal allow grouping the Sima de los Huesos hominins with different paleodemes into a Neanderthal clade. The dental evidence of the Sima de los Huesos hominins is key to suggest a complex model for the settlement of Europe during the Middle Pleistocene. During this period, different migrations of human groups probably coming from Southwest Asia, replacements, prolonged isolations, as well as hybridization and introgression processes would have contributed to the diversity of hominins in Europe.

Dental remains of the Middle Pleistocene hominins from the Sima de los Huesos site (Sierra de Atapuerca, Spain): Mandibular dentition

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The Middle Pleistocene site of the Sima de los Huesos (Sierra de Atapuerca, northern Spain) has yielded a considerable number of human fossils during the period 1984–2020. Among them, up to 314 mandibular teeth have been identified. In this second paper dedicated to the dentition we present the description of the eight dental classes of the mandible following the Arizona State University Dental Anthropology System (ASUDAS) classification. In addition, we show the mean mesiodistal and buccolingual diameters obtained in these teeth compared to those of Neanderthals and a modern human sample. The morphology of both the anterior and posterior teeth suggests a close relationship of the Sima de los Huesos hominins with the populations of the second half of the Middle Pleistocene of Europe and the Near East, as well as with the so-called classic Neanderthals of Europe. The combination of dental traits in these populations is characteristic and diagnostic and suggests grouping the Sima de los Huesos hominins with the other paleodemes in a Neanderthal clade. The dental evidence of the Sima de los Huesos hominins is key to propose a complex model for the settlement of Europe during the Middle Pleistocene. In this period, different migrations of human groups probably coming from Southwest Asia, replacements, prolonged isolations, as well as hybridization and introgression processes would have contributed to the diversity of hominins in Europe.

The Ratón Pérez collection: Modern deciduous human teeth at the Centro Nacional de Investigación sobre la Evolución Humana (Burgos, Spain)

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Objectives The aim of this report is to present the large deciduous tooth collection of identified children that is housed at the National Research Center on Human Evolution (CENIEH) in Burgos, Spain. Methods Yearly, members of the Dental Anthropology Group of the CENIEH are in charge of collecting the teeth and registering all the relevant information from the donors at the time of collection. In compliance with Spanish Law 14/2007 of July 3, 2007, on Biomedical Research (BOE-A-2007-12945), all individuals are guaranteed anonymity and confidentiality. When the donor hands in the tooth, they fill out a Donor Information Form and sign the Informed Consent Form. At the same time, another person completes the data label for the transparent polyethylene zip lock bag where the tooth is temporarily stored. All teeth are then transferred to the CENIEH Restoration lab, where the specialists apply the same protocol as for the fossil remains. Results Although the sample is still growing, from the first collection campaign in 2014 to date it comprises 2977 teeth of children whose ages of tooth loss are between 2 and 15 years. Each tooth is associated with basic information of the individuals and their parents and grandparents (sex, date, and place of birth, ancestry, country of residence), as well as important data about early life history (pregnancy duration, breastfeeding, bottle-feeding) and other relevant information provided by the donors (such as if they are twins, dental loss, or dental extraction). Conclusions Due to the scarcity of deciduous dental samples available, the Ratón Pérez collection represents a highly valuable sample for a wide range of disciplines such as forensic, dental, and anthropological fields among others.

Daily Distance Traveled Is Associated with Greater Brain Size in Primates

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PNG_SCI_Articles - Vidal-Cordasco-et-al.-2020-Daily-Distance-Traveled-Is-Associated-with-Greater

Explanations for the brain size increments through primate and, particularly, human evolution are numerous. Commonly, these hypotheses rely on the influence that behavioral and ecological variables have on brain size in extant primates, such as diet quality, social group size, or home range (HR) area. However, HR area does not reflect the time spent moving. As such, it has not been properly addressed whether the effort involved in movement could have affected brain size evolution in primates. This study aimed to test the influence of daily movement on primates’ brain sizes, controlling for these other behavioral and ecological factors. We used a large comparative dataset of extant primate species and phylogenetic comparative methods. Our results show a significant correlation between daily movement and brain mass, which is not explained by the influence of diet, social group size, HR, or body mass. Hence, from an evolutionary timescale, a longer daily movement distance is not a constraining factor for the energetic investment in a larger brain. On the contrary, increased mobility could have contributed to brain mass incrementations through evolution.