City in a spin as mystery monster washes up on New York riverbank

As any child knows, the steam breaking through the manhole covers in Manhattan in winter (and sometimes in summer too) comes from alligators in the sewers making cups of tea. Likewise, if an unidentifiable carcass washes up on the beach of the East River it must be an atrocious creature delivered from outer space.

Oddly, while the children figure out quite quickly that alligators in the subway system is nothing but silliness, the adults fall for the Martian invasion myth with remarkable frequency. In 2008, we got our knickers in a knot about the Montauk Monster, a bloated carcass that rolled ashore at the end of Long Island. But that was four years ago.

Thank goodness then for Denise Ginley, a freelance photographer, who on a stroll last Sunday on the eastern bank of Manhattan Isle, spotted something weird on the sand under the Brooklyn Bridge, leaped the fence, took a few snaps and – in a genius move for any freelancer needing attention – zipped the images to the city's social blogs.

The online party began faster than you could say "flying saucer". About the only explanation that has not b een offered so far is that this is the remains a galactic captain who fell accidentally from the bridge of his spaceship, landed on the spike of the Chrysler Building, from where he was pinged, mortally wounded, into the East River.

"We were horrified by it and we took some camera phone pictures and then finally we decided to come back with my camera and I got up the courage to climb over the fence and get closer to it," Ms Ginley told the site, ANIMAL. The headline writers called it the "East River Monster", while some speculated the body was that of a rat larger and more dangerous than any the world has ever seen.

The Parks Department then spoiled everything by telling anyone who asked it was in fact nothing more than a pig, presumably discarded by beach revellers somewhere upstream after a July cook-out. "We disposed of it," a spokesman said. Oh well. Yet something about the pig story doesn't quite convince. (And why a let a silly-season story die so quickly?) Was the Parks Department telling a porker to stop Gotham dissolving into an alien-invasion panic?

It's all in the toes. Pigs don't have toes, best anyone knows. They have trotters. But the pictures taken by Ms Ginley clearly show piggy pinkies.

Five on what almost look like little hands at the end of each leg. "I definitely agree that the feet are not pig-like at all," Ms Ginley confirmed to the New York Magazine blog, the Daily Intel. "No hooves or cloven feet to be seen – it definitely had five toes on all its paws, front and back."

So the mystery endures. All of Gotham is on edge and even the alligators have stopped making tea. What it definitely is not is a cousin of the Montauk Monster of 2008. That, rather boringly, turned out to be a semi-decomposed raccoon.