Limpet Shells from the Aterian Level 8 of El Harhoura 2 Cave (Témara, Morocco): Preservation State of Crossed-Foliated Layers

PLoS One. 2015 Sep 16;10(9):e0137162. doi: 10.1371/journal.pone.0137162. eCollection 2015.

Abstract

The exploitation of mollusks by the first anatomically modern humans is a central question for archaeologists. This paper focuses on level 8 (dated around ∼ 100 ka BP) of El Harhoura 2 Cave, located along the coastline in the Rabat-Témara region (Morocco). The large quantity of Patella sp. shells found in this level highlights questions regarding their origin and preservation. This study presents an estimation of the preservation status of these shells. We focus here on the diagenetic evolution of both the microstructural patterns and organic components of crossed-foliated shell layers, in order to assess the viability of further investigations based on shell layer minor elements, isotopic or biochemical compositions. The results show that the shells seem to be well conserved, with microstructural patterns preserved down to sub-micrometric scales, and that some organic components are still present in situ. But faint taphonomic degradations affecting both mineral and organic components are nonetheless evidenced, such as the disappearance of organic envelopes surrounding crossed-foliated lamellae, combined with a partial recrystallization of the lamellae. Our results provide a solid case-study of the early stages of the diagenetic evolution of crossed-foliated shell layers. Moreover, they highlight the fact that extreme caution must be taken before using fossil shells for palaeoenvironmental or geochronological reconstructions. Without thorough investigation, the alteration patterns illustrated here would easily have gone unnoticed. However, these degradations are liable to bias any proxy based on the elemental, isotopic or biochemical composition of the shells. This study also provides significant data concerning human subsistence behavior: the presence of notches and the good preservation state of limpet shells (no dissolution/recrystallization, no bioerosion and no abrasion/fragmentation aspects) would attest that limpets were gathered alive with tools by Middle Palaeolithic (Aterian) populations in North Africa for consumption.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animal Shells / anatomy & histology
  • Animal Shells / chemistry*
  • Animals
  • Biological Evolution
  • Caves*
  • Fossils
  • Gastropoda / anatomy & histology*
  • Morocco
  • Paleontology
  • Preservation, Biological / statistics & numerical data*

Grants and funding

This research received support from CNRS through the interdisciplinary action AIR-Archaeometry and from the SYNTHESIS Project http://www.synthesis.info/ which is financed by European Community Research Infrastructure Action under FP7 Integrating Activities Programme (the authors especially thank J. Spratt, A. Ball and L. Howard from the mineralogy department of NHM, London for their support). The authors would like to thank the Institut National des Sciences de l’Archéologie et du Patrimoine (dir. A. Akerraz), the Mission archéologique El Harhoura-Témara, funded by the Commission consultative des recherches archéologiques à l’étranger of Ministère des Affaires Etrangères et Européennes of France and the Ministry of Culture of Morocco. The authors also would like to thank the French Agence Nationale de la Recherche and the ANR-09-PEXT-004 MOHMIE project (dir. C. Denys) for the funding provided in the field work. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.