Andre Durenceau
Several lovely illustrations by Andre Durenceau from Roy Chapman Andrews' Nature's Ways, 1951. A few of these appear to be by other artists (I can't make out all the signatures) but only Durenceau is credited in the book. The printing is unfortunately poor, either out-of register or muddy somehow, but these still look pretty fantastic, with startling and not-entirely naturalistic color choices, as well as unusual compositions.
Yeah, this is obviously a photo, perhaps taken in a museum rather than in the wild, but I can't resist an ape.