Baby gorilla at Chicago's Lincoln Park Zoo. Todd Rosenberg Photography

A baby gorilla, born  nine days ago at Chicago’s Lincoln Park Zoo, was found dead this morning in its mother’s arms, according to zoo managers.

What went wrong? A necropsy will be done, the zoo told the Chicago Tribune, because until today there was no sign of trouble.

“We have been watching the mother and infant very closely since the birth and felt cautiously optimistic that the baby was healthy and being cared for appropriately,” said Megan Ross, the zoo’s vice president of animal care, according to the Tribune. “We are all surprised and very saddened by this tragic turn of events.”

Gorillas are intelligent animals, able to feel loss and mourn. The zoo let the baby’s mother, a 16-year-old gorilla named Bana, hold the baby for several hours “to make peace with what happened.” The zoo is open every day of the year (it’s a free and pleasant side trip if you visit Chicago, only three miles north of the Loop), but the African Apes building there was closed for the day.

The zoo staff had not yet given the baby a name. She was the first one born there in six years.