An image of a "dinosaur" from Kachina Bridge that scientists nicknamed Sinclair, as depicted by a young-Earth creationist (left) and as illustrated by scientists (right). The dark shading on the line drawing represents human engravings, while the light shading represents natural mud stains.

Ancient images that creationists claim are evidence of humans living alongside dinosaurs are at best just smeared pictures, scientists find.

At the site of Kachina Bridge in Utah — an immense sandstone formation resembling an arch more than 200 feet (60 meters) high and wide that was formed by the undercutting of a rock wall by flowing water — prehistoric cultures decorated the walls with paintings and engravings known as petroglyphs. Among them are what young-earth Earth creationists, who believe all life was created on the same day about 6,000 years ago, have said are depictions of dinosaurs, claiming these images as proof of their beliefs. [Scientists Hunt for Signs of Earth's Earliest Life]

Now, closer investigation reveals these ideas are just wishful thinking.

"The most important implication of these findings is that one of the creationist camp's favorite piece of 'evidence' for the coexistence of dinosaurs and humans — a dinosaur petroglyph — doesn't even exist," researcher Phil Senter, a paleontologist at Fayetteville State University in North Carolina, told LiveScience.

The researchers analyzed the four alleged dinosaur images with the naked eye and with binoculars and telephoto lenses while the pictures were illuminated by direct and indirect sunlight and when they were in shadow. [Image of dinosaur petroglyph]

"Dinosaur 1, which I've nicknamed Sinclair because it looks like the Sinclair Gas logo, really does look like a dino when seen with the naked eye," Senter said. "But the archaeologists who did the subsequent fieldwork knew exactly what they were looking at when they came out to examine the figure. This just goes to show that a trained eye can often see what an untrained eye cannot."

The researchers found the "neck" and "head" of Dinosaur 1 are a composite of two separate petroglyphs, while the "legs" appear to just be stains.

"I wonder if, during the process of weathering, chemicals from the man-made, [etched] part dripped down to form the 'legs,'" Senter said. "Lots of mineral stains are all over the canyon that contains Kachina Bridge."

"Until our study, this was the best dinosaur petroglyph — that is, the hardest to argue about, because it looked so much like a dinosaur that there was no way to interpret it as anything else," Senter said. "The 'best' dinosaur is now extinct."

"The 'dinos' other than Sinclair do not look like dinos at all, even with the naked eye," Senter added. "It is difficult for me to understand how anyone saw dinosaurs in those figures." In fact, the researchers say the four Kachina "dinosaurs" are "illusions produced by pareidolia," the psychological phenomenon responsible for people seeing faces or animals in clouds and the man in the moon.

Senter and archaeologist Sally Cole detailed their findings in the March issue of the journal Palaentologia Electronica.