Erika Constantine found the strange beast while out walking her dog in Melton Peter Demetre Park, near the US city of Charleston, South Carolina.
A fast-thinking Ms Constantine whipped out her camera to capture footage of her unsettling discovery.
The 25-year-old said: “I honestly did not know what it was.”
“I have lived here for about five years and I have never come across something like this.”
The animal, roughly the size of a small dog, is mainly bone, with a skeletal fin or rib cage poking out and a few teeth remaining.
Searching for answers, Miss Constantine posted her video online and was overwhelmed with responses – although it seems everyone is as baffled as she is.
She said: “I thought somebody would be like, ‘Oh, it’s like a seal’ and then I would go about my day but it stumped a lot of people.”
“There are so many theories as to what it is – the cops said it was a possum, it’s definitely not a possum. People were saying it’s a dog, people were saying it’s an iguana.”
“Somebody said it was a bobcat which was interesting because they do have similar ribcages.”
Among the more unusual suggestions were claims it could be the mythical Chupacabra, a legendary creature that attacks animals and consumes their blood.
The dog walker sent her footage to a professor at the College of Charleston hoping to get to the bottom of the mystery, but is yet to receive a response.
Miss Constantine now has her own theory on where the creature might come from – a secret island overrun by monkeys nearly 40 miles away and completely off-limits to human visitors.
She said: “It’s technically called Morgan Island but it’s nicknamed Monkey Island.”
“It’s not inhabited by humans, it’s all monkeys. That’s where all the monkeys that the government tested on live.”
“I think one of the monkeys from Monkey Island unfortunately might have got swept up in a current, the rip tide or whatever and then it made its way to Charleston.”
“It wouldn’t really be the first time, my friend actually found a monkey fossil on the beach a while back, so I think it just kinda got washed up here.”
The monkeys belong to National Institute of Allergy and Infectious Diseases, though the institute says it carries out no disease research on the island, beyond monitoring the monkeys.
The colony came from a primate research centre in La Parguera, Puerto Rico.
Visitors are not allowed on the island, which is owned and maintained by the South Carolina Department of Natural Resources.
