Humans have a curious structure in the middle of the upper lip, a vertical groove which is called philtrum, or infranasal depression. Most mammals have there a deep narrow groove, unlike the human philtrum. Do non-human primates & esp.chimpanzees have a humanlike philtrum?
Maybe this is of help:
Comparative microanatomy of the orbicularis oris muscle between chimpanzees and humans: evolutionary divergence of lip function
Carolyn R Rogers et al.ft für Morphologie und Anthropologie
Journal of Anatomy, 2009, 214 (1), pp. 36–44.
Casual observations on the philtrum of the lowland gorilla
Helmut O. Hofer
Zeitschrift für Morphologie und Anthropologie, 1985, 75 (2), pp. 239-243.
In addition to the aforementioned references, you can read the following papers:
Hofer, H.O. 1983. The external relief of the naso-labial integument of Pan troglodytes, Pan paniscus and Gorilla gorilla (Primates, Hominoidea). Z Morphol Anthropol. 73(3):309-22.
Sonntag, C.F. 1923. The anatomy, physiology and pathology of the chimpanzee. Proc. Zool. Soc. Lond. 22:323-429.
Many thanks a lot for the refs. According to these, a humanlike philtrum is not seen in other spp AFAICS. I sent the authors of the 2009 paper an email for possible further information.
Some people close their nostrils with their upper lip when they're diving, with the philtrum fitting the septum nasi, and I was wondering whether this could be rudiment of some nose-closing
system in human ancestors, perhaps cf prognathism as in H.erectus, or bigger noses as in neandertals?
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