A group of surfers in Santa Cruz County, Calif. stumbled upon a surprise Thursday. Sticking out of a rocky outcrop that is usually covered by water, even at low tide, was a giant set of fossilized vertebrae.

One of the dumbfounded surfers snapped a photo of the six to eight feet of bones, which were sticking out from a rock formation at Pleasure Point, a world-renowned surfing destination (home to the surf legend Jack O'Neill) that is one of only four dedicated "World Surfing Reserves."

The surfer, under the name Donkahones, posted his photo of the fossils to Reddit, the Internet message board, with the explanation that the group could see the bones because of an unusually low tide. The post was titled "So I went surfing and saw a dinosaur."

Experts disagreed.

"It is not a dinosaur," Gary Griggs, director of the Institute of Marine Sciences at the nearby University of California, Santa Cruz, told ABCnews.com. "The vertebrae are in what is called the Purisima formation, which is from the Pliocene, so they're three to five million years old. Which is relatively young. This is from way after the dinosaurs."

Griggs said he believes the vertebrae are "quite likely from an extinct whale species, probably one that looked a lot like whales today."

Griggs estimated the whale, when it lived, was anywhere from ten to twenty feet long.

A former student of Griggs', Curt Storlazzi of the United States Geological Survey, said that fossils are a common sight around Pleasure Point and that storms and sand probably wore down the rocks to make the fossilized bones visible.

"The area was once part of a shallow sea that contained a great many species," Storlazzi told ABCnews.com. "It is common to find many fossils in the area: marine mammals, shellfish, sharks, fish."

But the sheer size of Thursday's discovery is what makes it so notable.

"You find sharks teeth and fish bones, sure," Storlazzi said, "but a whole whale backbone sticking out of the rock, you don't see every day."

Neither Storlazzi nor Griggs could say what will come of the find.

"It was only just yesterday it was found," Storlazzi said. "It's state property. And excavating such a big find would require a big excavation. They may come and do some sort of sampling…we'll see."