The video above contains footage that some people may find distressing.
At two separate sites in the Democratic Republic of Congo, wild bonobo mothers have been observed eating their dead infants. It was a meal they shared with other bonobos, with the dominant female deciding who got access to the meat.
The behaviour has only been observed once before, which suggests it is extremely rare. You can see the unexpected behaviour in the video above.
One of the study's authors, Nahoko Tokuyama of Kyoto University in Japan, says she does not know why the behaviour occurred. "It may be explained by nutritional benefit. However, the number of cases is too small to find biological reasons."
She was shocked when she saw Hideo (pictured below), an older brother of one of the dead babies appearing to look "happy when he was eating his dead younger sibling". She says they treated the dead infants as they would any other meat.
The research was published in the journal Primates.
Melissa Hogenboom is BBC Earth's feature writer. She is @melissasuzanneh on Twitter.
Join over five million BBC Earth fans by liking us on Facebook, or follow us on Twitter and Instagram.
If you liked this story, sign up for the weekly bbc.com features newsletter called "If You Only Read 6 Things This Week". A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.