The Montauk Monster carcass, Ditch Plains beach, 2008

Saturday, July 12, 2008. Ditch Plains beach, Montauk, at the eastern tip of Long Island's South Fork. Jenna Hewitt, 26, was on the sand with three friends. Then they saw it.

A carcass. Bloated, hairless and sunbaked. Roughly the size of a large dog, by one account. The skin looked smooth and leathery. Where a snout should have been, there was something like a beak. Below it, sharp teeth. The limbs ended in elongated, claw-like digits.

"We didn't know what it was," Hewitt said. "We joked that maybe it was something from Plum Island." Courtney Fruin, one of the friends who found it, was blunter. "It had a beak, and it looked like a reptile in a dog's body." Ryan O'Shea studied the claws and front teeth. To him it looked like it could be "something vicious."

Hewitt took a picture with Rachel Goldberg's camera. It ran first in the East Hampton Independent. On July 29 it reached Gawker, passed along by a marketing firm. That same day Loren Coleman wrote on Cryptomundo: "For now, it remains the 'Montauk Monster.'" The name stuck. Christina Pampalone of East Northport came forward with her own photos from several angles. Rumours spread of a live one in the dunes, "hairless and was breathing quite heavily."

The body was gone. "They say an old guy came and carted it away," Hewitt told Scientific American. "He said, 'I'm going to mount it on my wall.'" Other accounts put it in the woods behind a man's house, or with a friend awaiting an autopsy. Newsday reported a local resident took it home. No scientist ever examined the remains.

Suspicion fell on Plum Island. Dr. Larry Barrett, director of the Plum Island Animal Disease Center, denied the animal came from there. Going by the visible canine tooth, he said it "may be a cat or raccoon." Larry Penny, East Hampton's Director of Natural Resources, called it a raccoon with its upper jaw missing. William Wise of Stony Brook University suspected a fake photo, or else a diseased dog or coyote.

Palaeozoologist Darren Naish made the detailed case. The "beak," he wrote, was "the naked premaxillary bones." The teeth, the slender limbs and the long digits all fit a raccoon, and "raccoons are actually surprisingly leggy." Decomposition and water had done the rest.

Gawker first wondered about viral marketing for Cartoon Network or the film Splinterheads. Both ideas were quickly debunked. In 2009 an anonymous man told blogger Drew Grant he was "one of those guys behind that Montauk monster thing." He said friends found a dead raccoon on Shelter Island, set it on a burning raft and pushed it out to sea. "This creature was honored with a viking funeral." No one has confirmed his story.

The Montauk Monster became a television fixture, from MonsterQuest to Ancient Aliens and Conspiracy Theory with Jesse Ventura. It inspired a song by Laura Stevenson and a novel by Hunter Shea. In 2009 a second, smaller carcass turned up in Montauk. That September in Panama, another pale body proved to be a sloth. The mystery carcass had gone viral, and it never quite went away.