molar size hominins

New study of molar size regulation in hominins

New study of molar size regulation in hominins

The Dental Anthropology Group at the CENIEH has tested the inhibitory cascade model to see whether it explains the size relationships and differences in shape between the different kinds of teeth, in the molar sample from the individuals identified at the Sima de los Huesos site in the Sierra de Atapuerca.
Mandíbula AT-1 de la Sima de los Huesos. Credits: Mario Modesto

The molar size relationship is one of the peculiar characteristics of the different species of hominins and various theories have been proposed to account for this, as well as the differences in shape between the different kinds of teeth (incisors, canines, premolars and molars). The latest theory, called the inhibitory cascade model, arose out of experiments with mice embryos, and in 2016 it was applied theoretically to fossil hominins, with satisfactory results.

It appeared that all hominins satisfy the inhibitory cascade model. In a paper by the Dental Anthropology Group at the Centro Nacional de Investigación sobre la evolución Humana (CENIEH), published recently in the Journal of Anatomy, this model was tested on the molar sample from the individuals identified at the Sima de los Huesos site, situated in the Sierra de Atapuerca (Burgos).

The results match the model generated in mice extraordinarily well, thus confirming the theory's utility once more. “Nevertheless, our conclusions have brought out an anomaly in the model, when it is applied to the oldest species of the genus Homo”, explains José María Bermúdez de Castro, Paleobiology Program Coordinator at the CENIEH and lead author of this work.

Increasing and decreasing patterns

In the genera Ardipithecus, Australopithecus and Paranthropus, as well as in Homo habilis, the size pattern is increasing and fits the premises of the inhibitory cascade model perfectly. The same thing happens in Homo sapiens, except that the pattern is decreasing, with the first molar larger than the second, which in turn is bigger than the third one (wisdom tooth).

Application of the inhibitory cascade model had led to the assumption that the switch from increasing to decreasing pattern would have arisen a little under two million years ago, perhaps coinciding with the transition between the genera Australopithecus and Homo. “However, in our work we noticed that this change could have required at least a million years to take place”, states Bermúdez de Castro.

The hominins from the Sima de los Huesos, which are around 430,000 years old, are a good example of that transition, whereas most specimens of Homo ergaster, Homo erectus, Homo antecessor and Homo heidelbergensis, as well as other species, do not fit the inhibitory cascade model. “Our idea is to continue our research to determine which genetic mechanisms lie behind this anomaly in the model”, says Bermúdez de Castro.

Full bibliographic information

Bermúdez de Castro et al. 2020. Testing the inhibitory cascade model in the Middle Pleistocene Sima de los Huesos (Sierra de Atapuerca, Spain) hominin sample. Journal of Anatomy. DOI: 10.1111/joa.13292
Press release from CENIEH.

Georadar reveals the unknown parts of the Sierra de Atapuerca caves

Georadar reveals the unknown parts of the Sierra de Atapuerca caves

The CENIEH has participated in a study led by Lucía Bermejo, in which this geophysical method was used to define the bottom part of the caves in the Trinchera del Ferrocarril sites
georadar Sierra de Atapuerca
GPR in Trinchera del Ferrocarril (Atapuerca). Credits: Miguel Ángel Martín

An international team of researchers from the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) and the University of Denver has managed to define the bottom part of the caves in the Trinchera del Ferrocarril sites (Cueva Peluda, Sima del Elefante, Galería and Gran Dolina), using georadar, revealing the unknown parts of these caves in the Sierra de Atapuerca (Burgos, Spain).

This non-invasive geophysical method, also known as ground penetrating radar (GPR), widely employed in archaeology because it is rapid and easy to apply, enables structures buried at different depths to be discovered. However, using it to study caves is usually discarded because the clayey sediments that fill them, being highly conductive, attenuate the radar signal, thus limiting its penetration capacity.

“Nevertheless, in our case this characteristic has served for studying the lower part of these caves, because we have been able to clearly distinguish the walls from the conduits, and from the sediments that fill them”, states Bermejo, lead author of this study, which was published recently in the journal Geomorphology.

It was possible to constrain the caves' depth by drilling two mechanical boreholes with core recovery, which have identified up to 17 meters of terrigenous fillings, such as in the case of the Galería site. Moreover, different types of sediments were discernible, thanks to which a possible conduit full of fluvial sediments was recorded, which would connect the lower level of Cueva Peluda with the lower part of Sima del Elefante.

Trinchera del Ferrocarril caves (Atapuerca). Credits: L. Bermejo et al

Quarrying activity

On the other hand, the information provided by the georadar and historical photographs have made it possible to establish how far the impact of the quarrying activity that took place at the Trinchera until the 1970s extended.

This activity was especially intensive between Cueva del Compresor, situated opposite the Galería site, and Gran Dolina, and it produced rubble fills up to 4 meters thick in the areas most impacted.

“All these data will help to optimize strategies for future excavations, as in this study it has been possible to identify the best preserved zones”, concludes Bermejo.

Full bibliographic information

Bermejo, L., Ortega, A. I., Parés, J. M., Campaña, I., Bermúdez de Castro, J. M., Carbonell, E., & Conyers, L. B. (2020). Karst features interpretation using ground-penetrating radar: A case study from the Sierra de Atapuerca, Spain. Geomorphology (0), 107311. doi: 10.1016/j.geomorph.2020.107311
Press release from CENIEH

molars Sima de los Huesos

The molars from Sima de los Huesos site share dental tissue traits with Homo antecessor and Neanderthals

The molars from Sima de los Huesos site share dental tissue traits with Homo antecessor and Neanderthals

The Dental Anthropology Group from CENIEH publishes a paper in PLOS ONE in which microscopy and micro-computed tomography are used to study the dental tissues in molars from European Middle Pleistocene individuals found at this site in Atapuerca, and compares these with species from the fossil record and modern humans
Distribution of enamel thickness in a lower molar from Sima de los Huesos compared with H. antecessor, Tighenif specimen and modern human. Credits: Martín-Francés et al.

The Dental Anthropology Group of the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) has published a paper this week in the journal PLOS ONE which marks another step forward in characterizing the individuals from the Sima de los Huesos site (Atapuerca, Burgos, Spain) and their relationship with Neanderthals and Homo antecessor, and helps to clarify the evolutionary steps that led to the dentition characteristic of Late Pleistocene hominins.

In this paper, whose lead author is the researcher Laura Martín-Francés (CENIEH and PACEA-University of Bordeaux), the dental tissues in the molars of the European Middle Pleistocene individuals found at Sima de los Huesos are analyzed, and compared with species in the fossil record and modern humans.

To conduct this comparative study, micro-computed tomography (mCT) and high-resolution images were used to examine the internal structure of 72 upper and lower molars from this site at Atapuerca, and these were contrasted against another 500 molars belonging to species from the genus Homo, extinct and extant, from Africa, Asia and Europe.

In the entire fossil record analyzed, only the Neanderthals present a unique structural pattern in molar tissues (enamel thickness, percentage of tissues and their distribution in the crown) which, in addition, they do not share with any other species. “In comparison with that record and with modern humans, Neanderthals had thin enamel, with a higher proportion of dentine and a more disperse distribution pattern”, says Martín-Francés.

It has been possible to determine that the molars from the Sima de los Huesos individuals had thick enamel and that, therefore, they do not share this trait with Neanderthals. Nevertheless, the two groups do share the same tissue distribution pattern.

“The results suggest that even though the complex of typically Neanderthal traits appeared later, certain aspects of the Neanderthal molar structure were already present in the hominins from Sima de los Huesos. In earlier work, we had identified this same pattern in Homo antecessor, another of the species recovered at Atapuerca”, adds Martín-Francés.

The Sima de los Huesos population, related genetically to the Neanderthals, represents a unique opportunity to study the appearance of the “typical” structural pattern of Neanderthal molar tissue.

Distribution of enamel thickness in an upper molar from Sima de los Huesos compared with H. antecessor, Neanderthal and modern human. Credits: Martín-Francés et al.

Full bibliographic information

Martín-Francés, L., Martinón-Torres, M., Martínez de Pinillos, M., García-Campos, C., Zanolli, C., Bayle, P., Modesto-Mata, M., Arsuaga, J. L., & Bermúdez de Castro, J. M. (2020). Crown tissue proportions and enamel thickness distribution in the Middle Pleistocene hominin molars from Sima de los Huesos (SH) population (Atapuerca, Spain). PLoS ONE, 15(6), e0233281. doi: 10.1371/journal.pone.0233281.
Press release from CENIEH

Cueva de los Toriles

Cueva de los Toriles site is dated to the Early-Middle Pleistocene by the presence of a primitive badger

Cueva de los Toriles site is dated to the Early-Middle Pleistocene by the presence of a primitive badger

The CENIEH has led a paper on this archaeological site located in Castilla-La Mancha (Spain), which makes clear its importance as one of the most significant enclaves with fossil remains from these chronologies in the southern Iberian plateau

Badger teeth. Credits: Daniel García Martínez

A team of researchers headed by Daniel Garcia Martínez, a paleoanthropologist at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), has just published a paper in the Journal of Iberian Geology on some remains of a primitive badger found in the Cueva de los Toriles (Carrizosa, Ciudad Real, Spain) which have allowed it to be dated to the Early-Middle Pleistocene: this archaeological site could potentially be a singular enclave with fossil remains from the southern Iberian plateau in these chronologies.

Even though there is currently no exact dating for the sedimentary deposits at this site in La Mancha, the finding of two lower molars of a mustelid, attributed to the species Meles cf. thorali, a primitive badger, has enabled their potential age to be checked, because this extinct mustelid is principally found in sites around 1 million years old.

As Alberto Valenciano, a specialist in mustelids from the University of Cape Town, explains: “In accordance with the presence of this badger species in the cave, we can tentatively assume an age ranging from the Late Pliocene up to the Middle Pleistocene”. In addition, as García Martínez comments: “These chronologies would be consistent with certain lithic tools recovered from the site”.

A natural corridor

Studying the southern Iberian plateau is primordial to revealing the population and movement of fauna in the Iberian Peninsula, because it functions as a natural corridor connecting the Central System and Iberian Range to the north with the Baetic Ranges to the south.

Cueva de los Toriles
Cueva de los Toriles site. Credits: Danie García Martínez

In the southern Iberian plateau, there are far fewer Pleistocene sites than in the northern plateau, where sites of world importance such as Atapuerca (Burgos) are found, because the eminently agricultural use of the land has caused many open-air sites to be altered or vanish.

“And while it is true that certain sites well-known to archaeologists are found in Ciudad Real, such as Albalá or El Sotillo, these are rich in lithic remains but poor in fossils, something which does not happen at Cueva de los Toriles where remains of macromammals have also been found, which could help to fill the gaps in our knowledge about this region”, states García Martínez.

“This cave is also an important site because of the enduring human presence stretching back to prehistory which we are seeing in our first investigations. A major milestone in the archaeology of Castilla-La Mancha and the southern sub-plateau", says Pedro R. Moya Maleno, from the Universidad Complutense de Madrid.

 

Full bibliographic information

 

García-Martínez, D., Valenciano, A., Suárez-Bilbao, A., Palancar, C. A., Megía García, I., Moreno, D., Campaña, I., & Moya-Maleno, P. R. (2020). New remains of a primitive badger from Cueva de los Toriles (Carrizosa, Castilla-La Mancha, Iberian Peninsula) suggest a new quaternary locality in the southern Iberian plateau. Journal of Iberian Geology (0). doi: 10.1007/s41513-020-00127-y

Press release from CENIEH


Dentition enables the sex of the youngest individuals from Sima de los Huesos to be estimated

Dentition enables the sex of the youngest individuals from Sima de los Huesos to be estimated

In a new study of sexual dimorphism carried out by the Dental Anthropology Group at the CENIEH, where a total of 32 dental pieces were analyzed, it has been possible to determine the sex of the immature specimens found at this site situated in the Sierra de Atapuerca

dentition Sima de los Huesos sexual dimorphism
Teeth from Sima de los Huesos. Credits: Cecilia García Campos

Today the Journal of Human Evolution publishes a study on sexual dimorphism led by Cecilia García Campos, a researcher in the Dental Anthropology Group at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) in which, thanks to the analysis of 32 dental pieces using micro-computed tomography, it has been possible to rise to the challenge posed, by estimating the sex of at least 15 individuals from the population of Sima de los Huesos site in the Sierra de Atapuerca (Burgos, Spain).

The extraordinary fossil collection recovered at this Middle Pleistocene site offers a unique opportunity for conducting demographic studies of the populations inhabiting Europe during that period. Nevertheless, many of the individuals in the Sima de los Huesos population are sub-adults or young adults who had not completed their development, so that their skeletons do not present clear secondary sexual traits that could help to determine their sex.

By contrast, these traits can be detected in their dentition, as the lead author of this work explains: “The teeth form early, allowing us to suggest a sex assignment even in those individuals who have not come through adolescence, so that dental anthropology turns out to be a very useful tool when endeavoring to study past populations with demographic structures similar to that in Sima de los Huesos”.

Dental histology

By studying the dentition of modern populations, in 2018 the CENIEH Dental Anthropology Group managed to identify a characteristic histological pattern to distinguish the canines belonging to male individuals from those of female individuals, and which offers an efficacy of 92.3%.

The application of this pattern at Sima de los Huesos has not only enabled the sex estimations proposed in earlier studies to be ratified, but also to suggest a sex assignment for the youngest individuals in the sample, something which had not been possible in previous work. All of this, therefore, has made clear the usefulness of dental histology for the assessment of sexual dimorphism and estimating sex in modern and past human populations.

“Specifically, this tool is especially useful in paleoanthropological settings, in which the other bone structures usually appear fragmented or are absent, and above all in those where sub-adults are better represented in their demographic structures”, comments García Campos.

 

Full bibliographic information

 

García-Campos, C., Modesto-Mata, M., Martinón-Torres, M., Martínez de Pinillos, M., Martín-Francés, L., Arsuaga, J.L., Bermúdez de Castro, J. M. 2020. Sexual dimorphism of the enamel and dentine dimensions of the permanent canines of the Middle Pleistocene hominins from Sima de los Huesos (Burgos, Spain). Journal of Human Evolution

 

Press release from CENIEH