%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Novello, A.
%A Barboni, D.
%A Sylvestre, Florence
%A Lebatard, A. E.
%A Pailles, C.
%A Bourles, D. L.
%A Likius, A.
%A Mackaye, H. T.
%A Vignaud, P.
%A Brunet, M.
%T Phytoliths indicate significant arboreal cover at Sahelanthropus type locality TM266 in northern Chad and a decrease in later sites
%D 2017
%L fdi:010070056
%G ENG
%J Journal of Human Evolution
%@ 0047-2484
%K Djurab ; Silica ; Grass ; Paleovegetation ; Paleoclimate ; Australopithecus bahrelghazali
%K TCHAD
%M ISI:000401217700005
%P 66-83
%R 10.1016/j.jhevol.2017.01.009
%U https://www.documentation.ird.fr/hor/fdi:010070056
%> https://www.documentation.ird.fr/intranet/publi/2017/06/010070056.pdf
%V 106
%W Horizon (IRD)
%X We analyzed phytolith and diatom remains preserved at 45 Miocene and Pliocene localities dated between 8 and 1 Ma in northern Chad (16-17 degrees N). Some of these localities yielded cranial remains, lower jaws, and teeth of the hominin species Australopithecus bahrelghazali (similar to 3.6 Ma) and Sahelanthropus tchadensis (similar to 7 Ma). Of the 111 sediment samples analyzed, 41 yielded phytoliths, 20 yielded diatoms, and seven yielded both phytoliths and diatoms. Freshwater planktonic and tychoplanktonic diatom species, indicative of lacustrine conditions, are dominant (>91%) in the samples. The phytolith assemblages indicate an opening of the vegetation and a general trend toward an expansion of grass-dominated environments during the time spanning the two hominin occurrences in Chad. The phytoliths suggest the presence of a mosaic environment, including closed forest patches, palm groves, and mixed/grassland formations, between 7.5 and 7 Ma, the replacement by palm grove-like vegetation at approximately 6.5-5 Ma, and the presence of exclusive grass-dominated formations after 4.5 Ma. The type-locality of S. tchadensis (TM266) was likely similar to modern palm grove formations with an arboreal cover percentage >= 40%. The type locality of A. bahrelghazali (KT12) was a grass-dominated ecosystem (likely savanna) with an unrated percentage of arboreal cover. Furthermore, the grass phytolith data support the existence of a (recurrent) Sahelian-like dry climate in northern Chad since at least 8 Ma. Therefore the local closed vegetation formations in the Djurab region at 7.5-7 Ma were sustained by aquatic systems (such as lakes or related rivers, marshes) rather than by extensive annual precipitation.
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