Tooth crown tissue proportions and enamel thickness in Early Pleistocene Homo antecessor molars (Atapuerca, Spain)

PLoS One. 2018 Oct 3;13(10):e0203334. doi: 10.1371/journal.pone.0203334. eCollection 2018.

Abstract

Tooth crown tissue proportions and enamel thickness distribution are considered reliable characters for inferring taxonomic identity, phylogenetic relationships, dietary and behavioural adaptations in fossil and extant hominids. While most Pleistocene hominins display variations from thick to hyper-thick enamel, Neanderthals exhibit relatively thinner. However, the chronological and geographical origin for the appearance of this typical Neanderthal condition is still unknown. The European late Early Pleistocene species Homo antecessor (Gran Dolina-TD6 site, Sierra de Atapuerca) represents an opportunity to investigate the appearance of the thin condition in the fossil record. In this study, we aim to test the hypothesis if H. antecessor molars approximates the Neanderthal condition for tissue proportions and enamel thickness. To do so, for the first time we characterised the molar inner structural organization in this Early Pleistocene hominin taxon (n = 17) and compared it to extinct and extant populations of the genus Homo from African, Asian and European origin (n = 355). The comparative sample includes maxillary and mandibular molars belonging to H. erectus, East and North African Homo, European Middle Pleistocene Homo, Neanderthals, and fossil and extant H. sapiens. We used high-resolution images to investigate the endostructural configuration of TD6 molars (tissue proportions, enamel thickness and distribution). TD6 permanent molars tend to exhibit on average thick absolute and relative enamel in 2D and 3D estimates, both in the complete crown and the lateral enamel. This condition is shared with the majority of extinct and extant hominin sample, except for Neanderthals and some isolated specimens. However, while the total crown percentage of dentine in TD6 globally resembles the low modern values, the lateral crown percentage of dentine tends to be much higher, closer to the Neanderthal signal. Similarly, the H. antecessor molar enamel distribution maps reveal a relative distribution pattern that is more similar to the Neanderthal condition (with the thickest enamel more spread at the periphery of the occlusal basin) rather than that of other fossil specimens and modern humans (with thicker cuspal enamel). Future studies on European Middle Pleistocene populations will provide more insights into the evolutionary trajectory of the typical Neanderthal dental structural organization.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Evolution*
  • Crowns
  • Dental Enamel / anatomy & histology
  • Dental Enamel / chemistry
  • Fossils / anatomy & histology*
  • Humans
  • Molar / anatomy & histology*
  • Neanderthals
  • Paleodontology
  • Phylogeny
  • Spain
  • Tooth Crown / anatomy & histology*

Grants and funding

This study was part of the Ministerio de Economía y Competitividad (MINECO), project CGL2015-65387-C3-3-P (JMBdC). This study received financial support from the British Academy (International Partnership and Mobility Scheme PM160019), the French State in the frame of the “Investments for the future” Programme IdEx Bordeaux, reference ANR-10-IDEX-03-02 (LM-F) and the Leakey Foundation through the personal support of Gordon Getty (2013) and Dub Crook (2014-2017) (MM-T). LM-F is beneficiary of an IdEx Post-Doctoral Research Grant, MMdP is beneficiary of a Fundación Atapuerca Post-Doctoral Research Grant. CG-C and MMdP have a predoctoral contract of the Junta de Castilla y León (BOCYL-D-02102014-14) co-financed by the European Social Funds through the Consejería de Educación. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.