For what is believed to be the very first time, researchers have observed the scene of a male marmoset bringing comfort to his partner as she lay dying -- remarkable new evidence which suggests that the emotional lives of non-human primates may be more complex than anyone had imagined before.

For the last few years, researcher have been studying the social workings of a group of the small New World monkeys in the forest of northeastern Brazil. Recently, the team observed the group's dominant female, identified as F1B, slip from a tree and strike her head on an object on the forest floor. For 45 minutes, she lay injured and writhing before dominant male M1B, her partner for three-and-a-half years, discovered her in distress.

What happened next, researchers are calling "remarkable."

"He immediately went to her," says primatologist Bruna Bezerra, to the BBC. "When I observed the dominant male approach the dying female, his gentle care and attention towards her left me astounded."

Over the next hour and 48 minutes, the male stayed by his partner's side, sniffing and embracing her as she slowly succumbed to her injuries.

As others in the group approached M1B drove them away. He also was observed exhibiting atypical behavior, such as making a alert calls for a non-existent predators and attempts at copulation.