BRIDGEPORT — Staff members at the Connecticut's Beardsley Zoo are investigating the unexpected death of two Goeldi’s monkeys that died this month following a sudden and unexplained illness, officials said.

The zoo is awaiting test results that might shed light on what killed the squirrel-sized South American primates known as Monty and Jovi, said Gregg Dancho, the zoo's director.

Dancho said the pair, which had been housed alone together in an enclosure inside the zoo's Rainforest Building, did not show any outward signs of sickness before succumbing to the illness.

He noted that a plastic guard created during the height of the COVID-19 pandemic that separates visitors from the monkeys has remained in place at the exhibit, and that staff members wear masks when working and interacting with primates.

"A lot of precautions were taken and it was very sudden," Dancho said. "That's what's concerning us."

Dancho said his staff has not yet uncovered any clues that might indicate what caused the animals, also known as Callimico monkeys, to become sick. He said he is hoping the ongoing necropsy, an autopsy performed on animals, will shed light on the situation.

In the meantime, Dancho said there is no evidence that any of the other more than 300 animals at the zoo contracted a similar illness.

"The animal care staff does a great job of taking care of their charges," Dancho said. "They're watching everything and seeing if anything is amiss — a sneeze, a cough, anything like that. There's been no indication that anything else is going on."

The news comes days before the zoo announced the sudden death of an ocelot, who died Thursday following surgery for artificial insemination.

The monkeys, Monty and Jovi, a male and female pair aged 15 and 4, respectively, had been a popular attraction at the zoo. The small exotic monkeys were known for being animated and inquisitive, and their death prompted an outpouring of grief on social media.

"They were very cute monkeys," Dancho said. "They moved around a lot and we have a lot of guests that have a close affinity to the animals here. They know that we care very much for them and they know our staff is very upset."

Like some other animals at the zoo, the Goeldi's monkeys did not strictly belong to the zoo but were a part of the Association of Zoos and Aquariums' Species Survival Plan program, which relies on a network of zoos to maintain a healthy and genetically diverse population of certain species.

Goeldi's monkeys, which are often covered in shaggy, black hair, are not an endangered species, but they are considered vulnerable due the reduction of their native habitat in the Amazon basin and the wildlife trade. The animals have been known to live as long as 21 years in captivity, according to the Smithsonian's National Zoo & Conservation Biology Institute.