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.

cultura muerte neandertales humanos modernos Nohemi Sala culture death neanderthals humans

Does the culture of death predate the Neanderthals and modern humans?

Does the culture of death predate the Neanderthals and modern humans?

The CENIEH researcher Nohemi Sala has been awarded 1.5 million euros by the European Research Council through an ERC-Starting Grant, to scour the fossil record for the roots and evolution of our ancestors' funerary behavior.

cultura muerte neandertales humanos modernos Nohemi Sala
Nohemi Sala, ERC-Starting Grant proyect IP.Credits: N. Sala

All societies existing today possess some kind of funerary culture, and this is one of the behaviors that takes us closest to how complex the human mind is. However, the emergence of this behavior is one of the most controversial topics in the field of human evolution. When did our ancestors start to acquire a culture of death? How was this behavior manifested over time and space? Did this practice appear independently in different species?

There are different ways to tackle these questions, and the more specific one of whether the culture ofdeath precedes Neanderthals and anatomically modern humans. To date, analyses in Paleolithic archaeology have centered on the archaeological context: that is, whether skeletons are preserved completely, the existence of a grave cut or whether objects that could be interpreted as symbolic elements or grave goods are present. This vision restricts funerary behavior almost exclusively to burials, something that was exceptionally rare before the Late Pleistocene, which began 127,000 years ago.

Thus, there is a need to find new methodological approaches so that what has been preserved up to our own time is right at the center: human bones. The European fossil record is a fundamental source of information due to the abundance of fossil skeletons. This is where forensic taphonomy, a discipline that can help to shed light on fundamental issues in this field, comes in. Applying this would be something like carrying out “autopsies” of human fossils to try to learn how they died and, above all, what happened to the remains of the individual between death and modern excavation.

This line of research has crystallized in a project entitled DEATHREVOL. The roots and evolution of the culture-of-death. A taphonomic research of the European Paleolithic record, which has been selected to receive financing under the European Union's Horizon 2020 Research and Innovation program, and which will be conducted over the next five years at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH).

“This is the first large-scale project centering on an exhaustive taphonomic study of the European fossil record”, explains the CENIEH taphonomy specialist Sala, a member of the Atapuerca research team and a researcher under the Juan de la Cierva-Incorporación program, who has obtained 1.5 million euros in funding for this project submitted to the 2020 call.

Carrying this out will require the participation of a large team of academics and a network of methods which include taphonomic analyses, virtual reconstructions for forensic analyses, studying spatial distribution patterns, the overall relations between different sites and mathematical models to interconnect the broad spectrum of data compiled.

Highly competitive projects

The European Research Council (ERC) projects known as “Starting Grants” are aimed at early-career researchers with post-doctoral experience of between 2 and 7 years, who have an outstanding research record and submit an excellent scientific project on the frontiers of knowledge. These are considered the most prestigious awards in the sphere of European research and, therefore, are highly competitive.

In the 2020 call, 436 researchers from 25 countries in the European Union and associated countries were selected, and 23 of the projects will be conducted at Spanish research centers. Of these 23, four are in the field of humanities and only one is centered on Paleoanthropology.

 

Press release from CENIEH on the Starting Grant for the research about the culture of death preceding Neanderthals and modern humans.


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