Chimpanzees recognize one another from their rear ends

Chimpanzees recognize one another from their rear ends
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Like the face in humans, chimpanzees derive important information about identity, attractiveness and health from the buttocks. [...] For chimpanzees, the buttocks are therefore very important in recognising one another at a single glance.
[...]
Buttocks inversion effect

Kret discovered that there is also a buttocks inversion effect in chimpanzees. She had test candidates -- humans and chimpanzees -- look at photos of faces and buttocks both upright and inverted. They could indicate on a touchscreen which faces and buttocks they recognised. The chimpanzees were faster in clicking on the buttocks when they were upright rather than inverted.
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As has been shown previously, humans recognise faces in an upright position faster than in an inverted position. The human test candidates recognised the buttocks just as quickly whether the photos were upright or inverted.
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https://www.sciencedaily.com/releases/2016/12/161201160756.htm
https://www.sciencedaily.com/releases/2016/12/161201160756.htm