comment on this calibration


 node name
Chimpanzee-Human     Look for this name in NCBI   Wikipedia   Animal Diversity Web
  recommended citations Benton et al. 2015
  node minimum age
6.5 Ma
Dating of the Sahelanthropus beds in Chad is indirect. Biostratigraphic evidence from fossil mammals, fish, and reptiles indicates that the unit is older than 5.33 Ma, and older than the Lukeino Formation of Kenya (the source of Orrorin), dated at 6.56 - 5.73 Ma from Ar/Ar dates on volcanic layers (Deino et al., 2002). The Chadian fossil may derive from equivalents to the lower fossiliferous units of the Nawata Formation at Lothagam, dated as 7.4 - 6.5 Ma (Vignaud et al., 2002). This might suggest a date for the sediments containing Sahelanthropus of 7.5 - 6.5 Ma, based on biostratigraphy and external dating. Thus, we determine a 6.5 Ma age for the minimum constraint on the human-chimp split.
  node maximum age
10 Ma
A range of ape taxa, Ankarapithecus from Turkey (10 Ma), Gigantopithecus from China (8 – 0.3 Ma), Lufengopithecus from China (10 Ma), Ouranopithecus from Greece (10 – 9 Ma), and Sivapithecus from Pakistan (10 – 7 Ma) give maximum ages of 10 Ma, early in the late Miocene, and these deposits have yielded no fossils attributable to either chimps or humans. This is taken as the soft maximum constraint on the human-chimp divergence.
 primary fossil used to date this node 
CNAR TM 266-01-060-1
Sahelanthropus chadensis , Brunet et al., 2002
Location relative to the calibrated node: Crown

[show fossil details]
     Locality: Toros-Menalla
     Stratum: Sahelanthropus beds
     Geological age: Miocene, Neogene, Cenozoic

More information in Fossilworks   PaleoBioDB

  phylogenetic justification
The skull of Sahelanthropus shows a mixture of primitive and advanced characters: the brain size, at 320–380 cm3, is comparable to that of chimpanzees, but the canine teeth are small, more like those of a human, and the prominent brow ridges are of the kind seen only in Homo. Sahelanthropus has generally been accepted, however, as a basal hominin (Cela-Conde and Ayala, 2003; Strait, 2013). Hominin apomorphies include incisors with a broad, deep, and round section, roots of premolars buccolingually narrow and in contact, and roots of molars curved (Emonet et al., 2014). Additional hominin apomorphies include the inferiorly facing foramen magnum, implying bipedalism, and the upper canine morphology showing no evidence of a honing complex (Strait, 2013).
  phylogenetic reference(s)
Emonet, E.-G., Andossa, L., Mackaye, H.T., and Brunet, M. 2014. Subocclusal ental morphology of Sahelanthropus tchadensis and the evolution of teeth in hominins. American Journal of Physical Anthropology, 153:116–123.
Strait, D.S. 2013. Human systematics, p. 37–54. In Begun, D.R. (ed.). A companion to paleoanthropology. John Wiley & Sons, Oxford.
Cela-Conde, C.J. and Ayala, F.J. 2003. Genera of the human lineage. Proceedings of the National Academy of Sciences, USA, 100:7684–689.
 tree image (click image for full size) 
tree image
Figure 11 of Benton et al. (2014)